1.
Celestial equator
–
The celestial equator is a great circle on the imaginary celestial sphere, in the same plane as the Earths equator. In other words, it is a projection of the terrestrial equator out into space, as a result of the Earths axial tilt, the celestial equator is inclined by 23. 4° with respect to the ecliptic plane. An observer standing on the Earths equator visualizes the celestial equator as a semicircle passing directly overhead through the zenith, as the observer moves north, the celestial equator tilts towards the opposite horizon. Celestial objects near the equator are visible worldwide, but they culminate the highest in the sky in the tropics. The celestial equator currently passes through these constellations, Celestial bodies other than Earth also have similarly defined celestial equators, Celestial pole Celestial sphere Declination Equatorial coordinate system
Celestial equator
–
The celestial equator is inclined by 23.4° to the
ecliptic plane. The image shows the relations between Earth's
axial tilt (or obliquity),
rotation axis and
plane of orbit.
2.
Hour circle
–
In astronomy, the hour circle of a celestial object is the great circle through the object and the celestial poles. It is perpendicular to the celestial equator, the declination of an object as observed on the celestial sphere is the angle measured along the hour circle of that object to the celestial equator. In other words, it is analogous to meridians or longitudes on a globe, a meridian on the celestial sphere matches an hour circle at any time. So called because the angle between the planes of the circles of two objects is sometimes measured in hours, one revolution being equivalent to 24 hours, or 1 hour being equivalent to 15°
Hour circle
–
Diagram illustrating the definition of the hour circle of a star.
3.
Declination
–
In astronomy, declination is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declinations angle is measured north or south of the celestial equator, the root of the word declination means a bending away or a bending down. It comes from the root as the words incline and recline. Declination in astronomy is comparable to geographic latitude, projected onto the celestial sphere, points north of the celestial equator have positive declinations, while those south have negative declinations. Any units of measure can be used for declination, but it is customarily measured in the degrees, minutes. Declinations with magnitudes greater than 90° do not occur, because the poles are the northernmost and southernmost points of the celestial sphere, the Earths axis rotates slowly westward about the poles of the ecliptic, completing one circuit in about 26,000 years. This effect, known as precession, causes the coordinates of stationary celestial objects to change continuously, therefore, equatorial coordinates are inherently relative to the year of their observation, and astronomers specify them with reference to a particular year, known as an epoch. Coordinates from different epochs must be rotated to match each other. The currently used standard epoch is J2000.0, which is January 1,2000 at 12,00 TT, the prefix J indicates that it is a Julian epoch. Prior to J2000.0, astronomers used the successive Besselian Epochs B1875.0, B1900.0, the declinations of Solar System objects change very rapidly compared to those of stars, due to orbital motion and close proximity. This similarly occurs in the Southern Hemisphere for objects with less than −90° − φ. An extreme example is the star which has a declination near to +90°. Circumpolar stars never dip below the horizon, conversely, there are other stars that never rise above the horizon, as seen from any given point on the Earths surface. Generally, if a star whose declination is δ is circumpolar for some observer, then a star whose declination is −δ never rises above the horizon, as seen by the same observer. Likewise, if a star is circumpolar for an observer at latitude φ, neglecting atmospheric refraction, declination is always 0° at east and west points of the horizon. At the north point, it is 90° − |φ|, and at the south point, from the poles, declination is uniform around the entire horizon, approximately 0°. Non-circumpolar stars are visible only during certain days or seasons of the year, the Suns declination varies with the seasons. As seen from arctic or antarctic latitudes, the Sun is circumpolar near the summer solstice, leading to the phenomenon of it being above the horizon at midnight
Declination
–
Right ascension (blue) and declination (green) as seen from outside the
celestial sphere.
4.
Celestial coordinate system
–
In astronomy, a celestial coordinate system is a system for specifying positions of celestial objects, satellites, planets, stars, galaxies, and so on. Coordinate systems can specify a position in 3-dimensional space, or merely the direction of the object on the celestial sphere, the coordinate systems are implemented in either spherical coordinates or rectangular coordinates. Spherical coordinates, projected on the sphere, are analogous to the geographic coordinate system used on the surface of the Earth. These differ in their choice of fundamental plane, which divides the sphere into two equal hemispheres along a great circle. Rectangular coordinates, in units, are simply the cartesian equivalent of the spherical coordinates, with the same fundamental plane. Each coordinate system is named after its choice of fundamental plane, the following table lists the common coordinate systems in use by the astronomical community. The fundamental plane divides the sphere into two equal hemispheres and defines the baseline for the latitudinal coordinates, similar to the equator in the geographic coordinate system. The poles are located at ±90° from the fundamental plane, the primary direction is the starting point of the longitudinal coordinates. The origin is the distance point, the center of the celestial sphere. The horizontal, or altitude-azimuth, system is based on the position of the observer on Earth, the positioning of a celestial object by the horizontal system varies with time, but is a useful coordinate system for locating and tracking objects for observers on Earth. It is based on the position of relative to an observers ideal horizon. The equatorial coordinate system is centered at Earths center, but fixed relative to the celestial poles, the coordinates are based on the location of stars relative to Earths equator if it were projected out to an infinite distance. The equatorial describes the sky as seen from the solar system, the equatorial system is the normal coordinate system for most professional and many amateur astronomers having an equatorial mount that follows the movement of the sky during the night. Celestial objects are found by adjusting the telescopes or other instruments scales so that they match the equatorial coordinates of the object to observe. There are also subdivisions into mean of date coordinates, which average out or ignore nutation, and true of date, the fundamental plane is the plane of the Earths orbit, called the ecliptic plane. The geocentric ecliptic system was the coordinate system for ancient astronomy and is still useful for computing the apparent motions of the Sun, Moon. The heliocentric ecliptic system describes the orbital movement around the Sun. The system is used for computing the positions of planets and other solar system bodies
Celestial coordinate system
–
Equirectangular plot of
declination vs
right ascension of stars brighter than
apparent magnitude 5 relative to the modern constellations, ecliptic and Milky Way (fuzzy band). To approximate the view of the night sky, right ascension increases from right to left.
5.
Celestial sphere
–
In astronomy and navigation, the celestial sphere is an imaginary sphere of arbitrarily large radius, concentric with Earth. All objects in the sky can be thought of as projected upon the inside surface of the celestial sphere. The celestial sphere is a tool for spherical astronomy, allowing observers to plot positions of objects in the sky when their distances are unknown or unimportant. Because astronomical objects are at such distances, casual observation of the sky offers no information on the actual distances. All objects seem equally far away, as if fixed to the inside of a sphere of large but unknown radius, which rotates from east to west overhead while underfoot, the celestial sphere can be considered to be infinite in radius. This means any point within it, including that occupied by the observer, all parallel planes will seem to intersect the sphere in a coincident great circle. On an infinite-radius celestial sphere, all observers see the things in the same direction. For some objects, this is over-simplified, objects which are relatively near to the observer will seem to change position against the distant celestial sphere if the observer moves far enough, say, from one side of the Earth to the other. This effect, known as parallax, can be represented as an offset from a mean position. The celestial sphere can be considered to be centered at the Earths center, the Suns center, or any convenient location. Individual observers can work out their own small offsets from the mean positions, in many cases in astronomy, the offsets are insignificant. The celestial sphere can thus be thought of as a kind of astronomical shorthand, for many rough uses, this position, as seen from the Earths center, is adequate. This greatly abbreviates the amount of detail necessary in such almanacs and these concepts are important for understanding celestial coordinate systems – frameworks for measuring the positions of objects in the sky. Certain reference lines and planes on Earth, when projected onto the celestial sphere and these include the Earths equator, axis, and the Earths orbit. At their intersections with the sphere, these form the celestial equator, the north and south celestial poles. As the celestial sphere is considered infinite in radius, all observers see the celestial equator, celestial poles, from these bases, directions toward objects in the sky can be quantified by constructing celestial coordinate systems. Similar to terrestrial longitude and latitude, the coordinate system specifies positions relative to the celestial equator and celestial poles. The ecliptic coordinate system specifies positions relative to the Earths orbit, besides the equatorial and ecliptic systems, some other celestial coordinate systems, such as the galactic coordinate system, are more appropriate for particular purposes
Celestial sphere
–
Celestial Sphere, 18th century.
Brooklyn Museum.
Celestial sphere
–
The
Earth rotating within a relatively small-diameter Earth-centered celestial sphere. Depicted here are stars (white), the
ecliptic (red), and lines of
right ascension and
declination (green) of the
equatorial coordinate system.
Celestial sphere
–
Celestial globe by
Jost Bürgi (1594)
6.
Equatorial coordinate system
–
The equatorial coordinate system is a celestial coordinate system widely used to specify the positions of celestial objects. The origin at the center of the Earth means the coordinates are geocentric, a right-handed convention means that coordinates are positive toward the north and toward the east in the fundamental plane. This description of the orientation of the frame is somewhat simplified. A slow motion of Earths axis, precession, causes a slow, continuous turning of the system westward about the poles of the ecliptic. Superimposed on this is a motion of the ecliptic. In order to fix the primary direction, these motions necessitate the specification of the equinox of a particular date, known as an epoch. The three most commonly used are, Mean equinox of an epoch is a fixed standard direction. Mean equinox of date is the intersection of the ecliptic of date with the mean equator, commonly used in planetary orbit calculation. True equinox of date is the intersection of the ecliptic of date with the true equator and this is the actual intersection of the two planes at any particular moment, with all motions accounted for. A position in the coordinate system is thus typically specified true equinox and equator of date, mean equinox and equator of J2000.0. Note that there is no mean ecliptic, as the ecliptic is not subject to small periodic oscillations, a stars spherical coordinates are often expressed as a pair, right ascension and declination, without a distance coordinate. The direction of distant objects is the same for all observers. Telescopes equipped with equatorial mounts and setting circles employ the equatorial coordinate system to find objects, setting circles in conjunction with a star chart or ephemeris allow the telescope to be easily pointed at known objects on the celestial sphere. The declination symbol δ, measures the distance of an object perpendicular to the celestial equator, positive to the north. For example, the celestial pole has a declination of +90°. The origin for declination is the equator, which is the projection of the Earths equator onto the celestial sphere. Declination is analogous to terrestrial latitude, the right ascension symbol α, measures the angular distance of an object eastward along the celestial equator from the vernal equinox to the hour circle passing through the object. The vernal equinox point is one of the two where the ecliptic intersects the celestial equator, there are = 15° in one hour of right ascension, 24h of right ascension around the entire celestial equator
Equatorial coordinate system
–
As seen from above the
Earth 's
north pole, a star's
local hour angle (LHA) for an observer near New York (red). Also depicted are the star's
right ascension and Greenwich hour angle (GHA), the
local mean sidereal time (LMST) and
Greenwich mean sidereal time (GMST). The symbol ʏ identifies the
vernal equinox direction.
7.
Ecliptic
–
The ecliptic is the apparent path of the Sun on the celestial sphere, and is the basis for the ecliptic coordinate system. It also refers to the plane of this path, which is coplanar with the orbit of Earth around the Sun, the motions as described above are simplifications. Due to the movement of Earth around the Earth–Moon center of mass, due to further perturbations by the other planets of the Solar System, the Earth–Moon barycenter wobbles slightly around a mean position in a complex fashion. The ecliptic is actually the apparent path of the Sun throughout the course of a year, because Earth takes one year to orbit the Sun, the apparent position of the Sun also takes the same length of time to make a complete circuit of the ecliptic. With slightly more than 365 days in one year, the Sun moves a little less than 1° eastward every day, again, this is a simplification, based on a hypothetical Earth that orbits at uniform speed around the Sun. The actual speed with which Earth orbits the Sun varies slightly during the year, for example, the Sun is north of the celestial equator for about 185 days of each year, and south of it for about 180 days. The variation of orbital speed accounts for part of the equation of time, if the equator is projected outward to the celestial sphere, forming the celestial equator, it crosses the ecliptic at two points known as the equinoxes. The Sun, in its apparent motion along the ecliptic, crosses the equator at these points, one from south to north. The crossing from south to north is known as the equinox, also known as the first point of Aries. The crossing from north to south is the equinox or descending node. Likewise, the ecliptic itself is not fixed, the gravitational perturbations of the other bodies of the Solar System cause a much smaller motion of the plane of Earths orbit, and hence of the ecliptic, known as planetary precession. The combined action of two motions is called general precession, and changes the position of the equinoxes by about 50 arc seconds per year. Once again, this is a simplification, periodic motions of the Moon and apparent periodic motions of the Sun cause short-term small-amplitude periodic oscillations of Earths axis, and hence the celestial equator, known as nutation. Obliquity of the ecliptic is the used by astronomers for the inclination of Earths equator with respect to the ecliptic. It is about 23. 4° and is currently decreasing 0.013 degrees per hundred years due to planetary perturbations, the angular value of the obliquity is found by observation of the motions of Earth and other planets over many years. From 1984, the Jet Propulsion Laboratorys DE series of computer-generated ephemerides took over as the ephemeris of the Astronomical Almanac. Obliquity based on DE200, which analyzed observations from 1911 to 1979, was calculated, jPLs fundamental ephemerides have been continually updated. J. Laskar computed an expression to order T10 good to 0″. 04/1000 years over 10,000 years, all of these expressions are for the mean obliquity, that is, without the nutation of the equator included
Ecliptic
Ecliptic
8.
Earth
–
Earth, otherwise known as the World, or the Globe, is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets, according to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago. Earths gravity interacts with objects in space, especially the Sun. During one orbit around the Sun, Earth rotates about its axis over 365 times, thus, Earths axis of rotation is tilted, producing seasonal variations on the planets surface. The gravitational interaction between the Earth and Moon causes ocean tides, stabilizes the Earths orientation on its axis, Earths lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earths surface is covered with water, mostly by its oceans, the remaining 29% is land consisting of continents and islands that together have many lakes, rivers and other sources of water that contribute to the hydrosphere. The majority of Earths polar regions are covered in ice, including the Antarctic ice sheet, Earths interior remains active with a solid iron inner core, a liquid outer core that generates the Earths magnetic field, and a convecting mantle that drives plate tectonics. Within the first billion years of Earths history, life appeared in the oceans and began to affect the Earths atmosphere and surface, some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. Since then, the combination of Earths distance from the Sun, physical properties, in the history of the Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely, over 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humans have developed diverse societies and cultures, politically, the world has about 200 sovereign states, the modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most often spelled eorðe. It has cognates in every Germanic language, and their proto-Germanic root has been reconstructed as *erþō, originally, earth was written in lowercase, and from early Middle English, its definite sense as the globe was expressed as the earth. By early Modern English, many nouns were capitalized, and the became the Earth. More recently, the name is simply given as Earth. House styles now vary, Oxford spelling recognizes the lowercase form as the most common, another convention capitalizes Earth when appearing as a name but writes it in lowercase when preceded by the. It almost always appears in lowercase in colloquial expressions such as what on earth are you doing, the oldest material found in the Solar System is dated to 4. 5672±0.0006 billion years ago. By 4. 54±0.04 Gya the primordial Earth had formed, the formation and evolution of Solar System bodies occurred along with the Sun
Earth
–
"
The Blue Marble " photograph of Earth, taken during the
Apollo 17 lunar mission in 1972
Earth
–
Artist's impression of the early Solar System's planetary disk
Earth
–
World map color-coded by relative height
Earth
–
The summit of
Chimborazo, in Ecuador, is the point on Earth's surface farthest from its center.
9.
Equator
–
The Equator usually refers to an imaginary line on the Earths surface equidistant from the North Pole and South Pole, dividing the Earth into the Northern Hemisphere and Southern Hemisphere. The Equator is about 40,075 kilometres long, some 78. 7% lies across water and 21. 3% over land, other planets and astronomical bodies have equators similarly defined. Generally, an equator is the intersection of the surface of a sphere with the plane that is perpendicular to the spheres axis of rotation. The latitude of the Earths equator is by definition 0° of arc, the equator is the only line of latitude which is also a great circle — that is, one whose plane passes through the center of the globe. The plane of Earths equator when projected outwards to the celestial sphere defines the celestial equator, in the cycle of Earths seasons, the plane of the equator passes through the Sun twice per year, at the March and September equinoxes. To an observer on the Earth, the Sun appears to travel North or South over the equator at these times, light rays from the center of the Sun are perpendicular to the surface of the Earth at the point of solar noon on the Equator. Locations on the Equator experience the quickest sunrises and sunsets because the sun moves nearly perpendicular to the horizon for most of the year. The Earth bulges slightly at the Equator, the diameter of the Earth is 12,750 kilometres. Because the Earth spins to the east, spacecraft must also launch to the east to take advantage of this Earth-boost of speed, seasons result from the yearly revolution of the Earth around the Sun and the tilt of the Earths axis relative to the plane of revolution. During the year the northern and southern hemispheres are inclined toward or away from the sun according to Earths position in its orbit, the hemisphere inclined toward the sun receives more sunlight and is in summer, while the other hemisphere receives less sun and is in winter. At the equinoxes, the Earths axis is not tilted toward the sun, instead it is perpendicular to the sun meaning that the day is about 12 hours long, as is the night, across the whole of the Earth. Near the Equator there is distinction between summer, winter, autumn, or spring. The temperatures are usually high year-round—with the exception of high mountains in South America, the temperature at the Equator can plummet during rainstorms. In many tropical regions people identify two seasons, the wet season and the dry season, but many places close to the Equator are on the oceans or rainy throughout the year, the seasons can vary depending on elevation and proximity to an ocean. The Equator lies mostly on the three largest oceans, the Pacific Ocean, the Atlantic Ocean, and the Indian Ocean. The highest point on the Equator is at the elevation of 4,690 metres, at 0°0′0″N 77°59′31″W and this is slightly above the snow line, and is the only place on the Equator where snow lies on the ground. At the Equator the snow line is around 1,000 metres lower than on Mount Everest, the Equator traverses the land of 11 countries, it also passes through two island nations, though without making a landfall in either. Starting at the Prime Meridian and heading eastwards, the Equator passes through, Despite its name, however, its island of Annobón is 155 km south of the Equator, and the rest of the country lies to the north
Equator
–
Left: A monument marking the Equator near the town of
Pontianak, Indonesia Right: Road sign marking the Equator near
Nanyuki, Kenya
Equator
Equator
–
The Equator marked as it crosses
Ilhéu das Rolas, in São Tomé and Príncipe
10.
Horizon
–
At many locations, the true horizon is obscured by trees, buildings, mountains, etc. and the resulting intersection of earth and sky is called the visible horizon. When looking at a sea from a shore, the part of the sea closest to the horizon is called the offing. The word horizon derives from the Greek ὁρίζων κύκλος horizōn kyklos, separating circle, from the verb ὁρίζω horizō, to divide, to separate, a pilot can also retain his or her spatial orientation by referring to the horizon. For observers near sea level the difference between this geometrical horizon and the horizon is imperceptible to the naked eye. In astronomy the horizon is the plane through the eyes of the observer. It is the plane of the horizontal coordinate system, the locus of points that have an altitude of zero degrees. While similar in ways to the horizon, in this context a horizon may be considered to be a plane in space. One typically sees further along the Earths curved surface than a simple geometric calculation allows for because of refraction error, the reverse happens if the ground is hotter than the air above it, as often happens in deserts, producing mirages. Examples, For an observer standing on the ground with h =1.70 metres, for an observer standing on the ground with h =2 metres, the horizon is at a distance of 5 kilometres. For an observer standing on a hill or tower of 100 metres in height, for an observer standing at the top of the Burj Khalifa, the horizon is at a distance of 103 kilometres. For an observer atop Mount Everest, the horizon is at a distance of 336 kilometres, with d in miles and h in feet, d ≈1.5 h ≈1.22 h. Examples, assuming no refraction, For an observer on the ground with eye level at h =5 ft 7 in, for an observer standing on a hill or tower 100 feet in height, the horizon is at a distance of 12.2 miles. For an observer on the summit of Aconcagua, the horizon to the west is at a distance of 184 miles. The secant-tangent theorem states that O C2 = O A × O B, the equation can also be derived using the Pythagorean theorem. Since the line of sight is a tangent to the Earth and this sets up a right triangle, with the sum of the radius and the height as the hypotenuse. Another relationship involves the distance s along the surface of the Earth to the horizon, with γ in radians, s = R γ. Solving for s gives s = R cos −1 R R + h, the distances d and s are nearly the same when the height of the object is negligible compared to the radius. If the observer is close to the surface of the earth, then it is valid to disregard h in the term, and the formula becomes d =2 R h
Horizon
–
A water horizon, in northern
Wisconsin, U.S.
Horizon
–
View of Earth's horizon as seen from
Space Shuttle Endeavour, 2002
Horizon
–
A view across a 20-km-wide bay in the coast of
Spain. Note the
curvature of the Earth hiding the base of the buildings on the far shore.
Horizon
–
The curvature of the horizon is easily seen in this photograph, taken from a space shuttle at an altitude of 226 km in 2008.
11.
Right angle
–
In geometry and trigonometry, a right angle is an angle that bisects the angle formed by two adjacent parts of a straight line. More precisely, if a ray is placed so that its endpoint is on a line, as a rotation, a right angle corresponds to a quarter turn. The presence of an angle in a triangle is the defining factor for right triangles. The term is a calque of Latin angulus rectus, here rectus means upright, in Unicode, the symbol for a right angle is U+221F ∟ Right angle. It should not be confused with the similarly shaped symbol U+231E ⌞ Bottom left corner, related symbols are U+22BE ⊾ Right angle with arc, U+299C ⦜ Right angle variant with square, and U+299D ⦝ Measured right angle with dot. The symbol for an angle, an arc, with a dot, is used in some European countries, including German-speaking countries and Poland. Right angles are fundamental in Euclids Elements and they are defined in Book 1, definition 10, which also defines perpendicular lines. Euclid uses right angles in definitions 11 and 12 to define acute angles, two angles are called complementary if their sum is a right angle. Book 1 Postulate 4 states that all angles are equal. Euclids commentator Proclus gave a proof of this using the previous postulates. Saccheri gave a proof as well but using a more explicit assumption, in Hilberts axiomatization of geometry this statement is given as a theorem, but only after much groundwork. A right angle may be expressed in different units, 1/4 turn, 90° π/2 radians 100 grad 8 points 6 hours Throughout history carpenters and masons have known a quick way to confirm if an angle is a true right angle. It is based on the most widely known Pythagorean triple and so called the Rule of 3-4-5 and this measurement can be made quickly and without technical instruments. The geometric law behind the measurement is the Pythagorean theorem, Thales theorem states that an angle inscribed in a semicircle is a right angle. Two application examples in which the angle and the Thales theorem are included. Cartesian coordinate system Orthogonality Perpendicular Rectangle Types of angles Wentworth, G. A, Euclid, commentary and trans. by T. L. Heath Elements Vol.1 Google Books
Right angle
–
A right angle is equal to 90 degrees.
12.
Oblique angle
–
In planar geometry, an angle is the figure formed by two rays, called the sides of the angle, sharing a common endpoint, called the vertex of the angle. Angles formed by two rays lie in a plane, but this plane does not have to be a Euclidean plane, Angles are also formed by the intersection of two planes in Euclidean and other spaces. Angles formed by the intersection of two curves in a plane are defined as the angle determined by the tangent rays at the point of intersection. Similar statements hold in space, for example, the angle formed by two great circles on a sphere is the dihedral angle between the planes determined by the great circles. Angle is also used to designate the measure of an angle or of a rotation and this measure is the ratio of the length of a circular arc to its radius. In the case of an angle, the arc is centered at the vertex. In the case of a rotation, the arc is centered at the center of the rotation and delimited by any other point and its image by the rotation. The word angle comes from the Latin word angulus, meaning corner, cognate words are the Greek ἀγκύλος, meaning crooked, curved, both are connected with the Proto-Indo-European root *ank-, meaning to bend or bow. Euclid defines a plane angle as the inclination to each other, in a plane, according to Proclus an angle must be either a quality or a quantity, or a relationship. In mathematical expressions, it is common to use Greek letters to serve as variables standing for the size of some angle, lower case Roman letters are also used, as are upper case Roman letters in the context of polygons. See the figures in this article for examples, in geometric figures, angles may also be identified by the labels attached to the three points that define them. For example, the angle at vertex A enclosed by the rays AB, sometimes, where there is no risk of confusion, the angle may be referred to simply by its vertex. However, in geometrical situations it is obvious from context that the positive angle less than or equal to 180 degrees is meant. Otherwise, a convention may be adopted so that ∠BAC always refers to the angle from B to C. Angles smaller than an angle are called acute angles. An angle equal to 1/4 turn is called a right angle, two lines that form a right angle are said to be normal, orthogonal, or perpendicular. Angles larger than an angle and smaller than a straight angle are called obtuse angles. An angle equal to 1/2 turn is called a straight angle, Angles larger than a straight angle but less than 1 turn are called reflex angles
Oblique angle
–
An angle enclosed by rays emanating from a vertex.
13.
First Point of Aries
–
An equinox is the moment in which the plane of Earths equator passes through the center of the Sun, which occurs twice each year, around 20 March and 23 September. On an equinox, day and night are of equal duration all over the planet. They are not exactly equal, however, due to the size of the sun. To avoid this ambiguity, the word equilux is sometimes used to mean a day in which the durations of light, see Length of equinoctial day and night for further discussion. The word is derived from the Latin aequinoctium, aequus and nox, the equinoxes are the only times when the solar terminator is perpendicular to the equator. As a result, the northern and southern hemispheres are equally illuminated, the word comes from Latin equi or equal and nox meaning night. In other words, the equinoxes are the times when the subsolar point is on the equator. The subsolar point crosses the equator moving northward at the March equinox, the equinoxes, along with solstices, are directly related to the seasons of the year. In the southern hemisphere, the equinox occurs in September. When Julius Caesar established the Julian calendar in 45 BC, he set 25 March as the date of the spring equinox. Because the Julian year is longer than the tropical year. By 1500 AD, it had drifted backwards to 11 March and this drift induced Pope Gregory XIII to create a modern Gregorian calendar. However, the leap year intervals in his calendar were not smooth and this causes the equinox to oscillate by about 53 hours around its mean position. This in turn raised the possibility that it could fall on 22 March, the astronomers chose the appropriate number of days to omit so that the equinox would swing from 19 to 21 March but never fall on the 22nd. Vernal equinox and Autumnal equinox, these names are direct derivatives of Latin. The equivalent common language English terms spring equinox and autumn equinox are even more ambiguous, March equinox and September equinox, names referring to the months of the year they occur, with no ambiguity as to which hemisphere is the context. They are still not universal, however, as not all use a solar-based calendar where the equinoxes occur every year in the same month. Northward equinox and southward equinox, names referring to the apparent direction of motion of the Sun
First Point of Aries
–
The Earth in its orbit around the Sun causes the Sun to appear on the celestial sphere moving over the
ecliptic (red), which is tilted on the
Equator (white)
First Point of Aries
–
Illumination of
Earth by the
Sun at the March equinox
First Point of Aries
–
Diagram of the Earth's
seasons as seen from the north. Far right: December solstice.
First Point of Aries
–
Diagram of the Earth's seasons as seen from the south. Far left: June solstice.
14.
Sun
–
The Sun is the star at the center of the Solar System. It is a perfect sphere of hot plasma, with internal convective motion that generates a magnetic field via a dynamo process. It is by far the most important source of energy for life on Earth. Its diameter is about 109 times that of Earth, and its mass is about 330,000 times that of Earth, accounting for about 99. 86% of the total mass of the Solar System. About three quarters of the Suns mass consists of hydrogen, the rest is mostly helium, with smaller quantities of heavier elements, including oxygen, carbon, neon. The Sun is a G-type main-sequence star based on its spectral class and it formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into a disk that became the Solar System. The central mass became so hot and dense that it eventually initiated nuclear fusion in its core and it is thought that almost all stars form by this process. The Sun is roughly middle-aged, it has not changed dramatically for more than four billion years and it is calculated that the Sun will become sufficiently large enough to engulf the current orbits of Mercury, Venus, and probably Earth. The enormous effect of the Sun on Earth has been recognized since prehistoric times, the synodic rotation of Earth and its orbit around the Sun are the basis of the solar calendar, which is the predominant calendar in use today. The English proper name Sun developed from Old English sunne and may be related to south, all Germanic terms for the Sun stem from Proto-Germanic *sunnōn. The English weekday name Sunday stems from Old English and is ultimately a result of a Germanic interpretation of Latin dies solis, the Latin name for the Sun, Sol, is not common in general English language use, the adjectival form is the related word solar. The term sol is used by planetary astronomers to refer to the duration of a solar day on another planet. A mean Earth solar day is approximately 24 hours, whereas a mean Martian sol is 24 hours,39 minutes, and 35.244 seconds. From at least the 4th Dynasty of Ancient Egypt, the Sun was worshipped as the god Ra, portrayed as a falcon-headed divinity surmounted by the solar disk, and surrounded by a serpent. In the New Empire period, the Sun became identified with the dung beetle, in the form of the Sun disc Aten, the Sun had a brief resurgence during the Amarna Period when it again became the preeminent, if not only, divinity for the Pharaoh Akhenaton. The Sun is viewed as a goddess in Germanic paganism, Sól/Sunna, in ancient Roman culture, Sunday was the day of the Sun god. It was adopted as the Sabbath day by Christians who did not have a Jewish background, the symbol of light was a pagan device adopted by Christians, and perhaps the most important one that did not come from Jewish traditions
Sun
–
The Sun in visible wavelength with filtered white light on 8 July 2014. Characteristic
limb darkening and numerous
sunspots are visible.
Sun
–
During a total
solar eclipse, the solar
corona can be seen with the naked eye, during the brief period of totality.
Sun
–
Taken by
Hinode 's Solar Optical Telescope on 12 January 2007, this image of the Sun reveals the filamentary nature of the plasma connecting regions of different magnetic polarity.
Sun
–
Visible light photograph of sunspot, 13 December 2006
15.
Equinox
–
An equinox is the moment in which the plane of Earths equator passes through the center of the Sun, which occurs twice each year, around 20 March and 23 September. On an equinox, day and night are of equal duration all over the planet. They are not exactly equal, however, due to the size of the sun. To avoid this ambiguity, the word equilux is sometimes used to mean a day in which the durations of light, see Length of equinoctial day and night for further discussion. The word is derived from the Latin aequinoctium, aequus and nox, the equinoxes are the only times when the solar terminator is perpendicular to the equator. As a result, the northern and southern hemispheres are equally illuminated, the word comes from Latin equi or equal and nox meaning night. In other words, the equinoxes are the times when the subsolar point is on the equator. The subsolar point crosses the equator moving northward at the March equinox, the equinoxes, along with solstices, are directly related to the seasons of the year. In the southern hemisphere, the equinox occurs in September. When Julius Caesar established the Julian calendar in 45 BC, he set 25 March as the date of the spring equinox. Because the Julian year is longer than the tropical year. By 1500 AD, it had drifted backwards to 11 March and this drift induced Pope Gregory XIII to create a modern Gregorian calendar. However, the leap year intervals in his calendar were not smooth and this causes the equinox to oscillate by about 53 hours around its mean position. This in turn raised the possibility that it could fall on 22 March, the astronomers chose the appropriate number of days to omit so that the equinox would swing from 19 to 21 March but never fall on the 22nd. Vernal equinox and Autumnal equinox, these names are direct derivatives of Latin. The equivalent common language English terms spring equinox and autumn equinox are even more ambiguous, March equinox and September equinox, names referring to the months of the year they occur, with no ambiguity as to which hemisphere is the context. They are still not universal, however, as not all use a solar-based calendar where the equinoxes occur every year in the same month. Northward equinox and southward equinox, names referring to the apparent direction of motion of the Sun
Equinox
–
The Earth in its orbit around the Sun causes the Sun to appear on the celestial sphere moving over the
ecliptic (red), which is tilted on the
Equator (white)
Equinox
–
Contour plot of the hours of daylight as a function of latitude and day of the year, showing approximately 12 hours of daylight at all latitudes during the equinoxes
Equinox
–
Diagram of the Earth's
seasons as seen from the north. Far right: December solstice.
Equinox
–
Diagram of the Earth's seasons as seen from the south. Far left: June solstice.
16.
Meridian circle
–
The meridian circle is an instrument for timing of the passage of stars across the local meridian, an event known as a transit, while at the same time measuring their angular distance from the nadir. Meridian telescopes rely on the rotation of the Earth to bring objects into their field of view and are mounted on a fixed, horizontal, east–west axis. The similar transit instrument, transit circle or transit telescope is mounted on a horizontal axis. For instance, a surveyors theodolite can function as an instrument if its telescope is capable of a full revolution about the horizontal axis. Meridian circles are called by these names, although they are less specific. For many years, transit timings were the most accurate method of measuring the positions of heavenly bodies, before spectroscopy, photography, and the perfection of reflecting telescopes, the measuring of positions was the major work of observatories. Revolving the telescope about its axis moves it directly in declination, all objects in the sky are subject to the distortion of atmospheric refraction, which tends to make objects appear slightly higher in the sky than they actually are. At the meridian, this distortion is in only, and is easily accounted for, elsewhere in the sky. Such complex analysis is not conducive to high precision, the state of the art of meridian instruments of the late 19th and early 20th century is described here, giving some idea of the precise methods of construction, operation and adjustment employed. The earliest transit telescope was not placed in the middle of the axis, later, it was usually placed in the centre of the axis, which consisted of one piece of brass or gun metal with turned cylindrical steel pivots at each end. Several instruments were made entirely of steel, which was more rigid than brass. The pivots rested on V-shaped bearings, either set into stone or brick piers which supported the instrument. The temperature of the bearings was monitored by thermometers, the piers were usually separate from the foundation of the building, to prevent transmission of vibration from the building to the telescope. In some cases, the counterweight pushed up on the bearing from below, the bearings were set nearly in a true east–west line, but fine adjustment was possible by horizontal and vertical screws. A spirit level was used to monitor for any inclination of the axis to the horizon, eccentricity of the telescopes axis was accounted for, in some cases, by providing another telescope through the axis itself. By observing the motion of a star through this axis telescope as the main telescope was rotated, the shape of the pivots. Near each end of the axis, attached to the axis, generally of 3 feet to 3.5 ft diameter, it was divided to 2 or 5 arcminutes, on a slip of silver set into the face of the circle near the circumference. These graduations were read by microscopes, generally four for each circle, mounted to the piers or a framework surrounding the axis, by averaging the four readings the eccentricity and the errors of graduation were greatly reduced
Meridian circle
–
Groombridge transit circle of 1806
Meridian circle
–
Meridian circle at Saint Petersburg Kunstkamera, built by T.L. Ertel, Germany, 1828
Meridian circle
–
Meridian circle at the
Kuffner observatory, Vienna, Austria, built by Repsold & Sons, Hamburg, 1886. Note the counterweights, the short, green cylindrical objects at the outer top of the mechanism, and the four long, thin, microscopes for reading the circles.
Meridian circle
–
Chabot Space & Science Center's meridian transit telescope, built by Fauth, 1885. Note the observer's chair between the piers, and the narrow opening in the wall and roof for access to the sky. Because the telescope observes only in the meridian, no rotating dome is necessary.
17.
Degree (angle)
–
A degree, usually denoted by °, is a measurement of a plane angle, defined so that a full rotation is 360 degrees. It is not an SI unit, as the SI unit of measure is the radian. Because a full rotation equals 2π radians, one degree is equivalent to π/180 radians, the original motivation for choosing the degree as a unit of rotations and angles is unknown. One theory states that it is related to the fact that 360 is approximately the number of days in a year. Ancient astronomers noticed that the sun, which follows through the path over the course of the year. Some ancient calendars, such as the Persian calendar, used 360 days for a year, the use of a calendar with 360 days may be related to the use of sexagesimal numbers. The earliest trigonometry, used by the Babylonian astronomers and their Greek successors, was based on chords of a circle, a chord of length equal to the radius made a natural base quantity. One sixtieth of this, using their standard sexagesimal divisions, was a degree, Aristarchus of Samos and Hipparchus seem to have been among the first Greek scientists to exploit Babylonian astronomical knowledge and techniques systematically. Timocharis, Aristarchus, Aristillus, Archimedes, and Hipparchus were the first Greeks known to divide the circle in 360 degrees of 60 arc minutes, eratosthenes used a simpler sexagesimal system dividing a circle into 60 parts. Furthermore, it is divisible by every number from 1 to 10 except 7 and this property has many useful applications, such as dividing the world into 24 time zones, each of which is nominally 15° of longitude, to correlate with the established 24-hour day convention. Finally, it may be the case more than one of these factors has come into play. For many practical purposes, a degree is a small enough angle that whole degrees provide sufficient precision. When this is not the case, as in astronomy or for geographic coordinates, degree measurements may be written using decimal degrees, with the symbol behind the decimals. Alternatively, the sexagesimal unit subdivisions can be used. One degree is divided into 60 minutes, and one minute into 60 seconds, use of degrees-minutes-seconds is also called DMS notation. These subdivisions, also called the arcminute and arcsecond, are represented by a single and double prime. For example,40. 1875° = 40° 11′ 15″, or, using quotation mark characters, additional precision can be provided using decimals for the arcseconds component. The older system of thirds, fourths, etc. which continues the sexagesimal unit subdivision, was used by al-Kashi and other ancient astronomers, but is rarely used today
Degree (angle)
–
One degree (shown in red) and eighty nine (shown in blue)
18.
Arcminute
–
A minute of arc, arcminute, arc minute, or minute arc is a unit of angular measurement equal to 1/60 of one degree. Since one degree is 1/360 of a turn, one minute of arc is 1/21600 of a turn, a second of arc, arcsecond, or arc second is 1/60 of an arcminute, 1/3600 of a degree, 1/1296000 of a turn, and π/648000 of a radian. To express even smaller angles, standard SI prefixes can be employed, the number of square arcminutes in a complete sphere is 4 π2 =466560000 π ≈148510660 square arcminutes. The standard symbol for marking the arcminute is the prime, though a single quote is used where only ASCII characters are permitted. One arcminute is thus written 1′ and it is also abbreviated as arcmin or amin or, less commonly, the prime with a circumflex over it. The standard symbol for the arcsecond is the prime, though a double quote is commonly used where only ASCII characters are permitted. One arcsecond is thus written 1″ and it is also abbreviated as arcsec or asec. In celestial navigation, seconds of arc are used in calculations. This notation has been carried over into marine GPS receivers, which normally display latitude and longitude in the format by default. An arcsecond is approximately the angle subtended by a U. S. dime coin at a distance of 4 kilometres, a milliarcsecond is about the size of a dime atop the Eiffel Tower as seen from New York City. A microarcsecond is about the size of a period at the end of a sentence in the Apollo mission manuals left on the Moon as seen from Earth, since antiquity the arcminute and arcsecond have been used in astronomy. The principal exception is Right ascension in equatorial coordinates, which is measured in units of hours, minutes. These small angles may also be written in milliarcseconds, or thousandths of an arcsecond, the unit of distance, the parsec, named from the parallax of one arcsecond, was developed for such parallax measurements. It is the distance at which the radius of the Earths orbit would subtend an angle of one arcsecond. The ESA astrometric space probe Gaia is hoped to measure star positions to 20 microarcseconds when it begins producing catalog positions sometime after 2016, there are about 1.3 trillion µas in a turn. Currently the best catalog positions of stars actually measured are in terms of milliarcseconds, apart from the Sun, the star with the largest angular diameter from Earth is R Doradus, a red supergiant with a diameter of 0.05 arcsecond. The dwarf planet Pluto has proven difficult to resolve because its angular diameter is about 0.1 arcsecond, space telescopes are not affected by the Earths atmosphere but are diffraction limited. For example, the Hubble space telescope can reach a size of stars down to about 0. 1″
Arcminute
–
Comparison of angular diameter of the Sun, Moon, planets and the International Space Station. To get a true representation of the sizes, view the image at a distance of 103 times the width of the "Moon: max." circle. For example, if this circle is 10 cm wide on your monitor, view it from 10.3 m away.
19.
Arcsecond
–
A minute of arc, arcminute, arc minute, or minute arc is a unit of angular measurement equal to 1/60 of one degree. Since one degree is 1/360 of a turn, one minute of arc is 1/21600 of a turn, a second of arc, arcsecond, or arc second is 1/60 of an arcminute, 1/3600 of a degree, 1/1296000 of a turn, and π/648000 of a radian. To express even smaller angles, standard SI prefixes can be employed, the number of square arcminutes in a complete sphere is 4 π2 =466560000 π ≈148510660 square arcminutes. The standard symbol for marking the arcminute is the prime, though a single quote is used where only ASCII characters are permitted. One arcminute is thus written 1′ and it is also abbreviated as arcmin or amin or, less commonly, the prime with a circumflex over it. The standard symbol for the arcsecond is the prime, though a double quote is commonly used where only ASCII characters are permitted. One arcsecond is thus written 1″ and it is also abbreviated as arcsec or asec. In celestial navigation, seconds of arc are used in calculations. This notation has been carried over into marine GPS receivers, which normally display latitude and longitude in the format by default. An arcsecond is approximately the angle subtended by a U. S. dime coin at a distance of 4 kilometres, a milliarcsecond is about the size of a dime atop the Eiffel Tower as seen from New York City. A microarcsecond is about the size of a period at the end of a sentence in the Apollo mission manuals left on the Moon as seen from Earth, since antiquity the arcminute and arcsecond have been used in astronomy. The principal exception is Right ascension in equatorial coordinates, which is measured in units of hours, minutes. These small angles may also be written in milliarcseconds, or thousandths of an arcsecond, the unit of distance, the parsec, named from the parallax of one arcsecond, was developed for such parallax measurements. It is the distance at which the radius of the Earths orbit would subtend an angle of one arcsecond. The ESA astrometric space probe Gaia is hoped to measure star positions to 20 microarcseconds when it begins producing catalog positions sometime after 2016, there are about 1.3 trillion µas in a turn. Currently the best catalog positions of stars actually measured are in terms of milliarcseconds, apart from the Sun, the star with the largest angular diameter from Earth is R Doradus, a red supergiant with a diameter of 0.05 arcsecond. The dwarf planet Pluto has proven difficult to resolve because its angular diameter is about 0.1 arcsecond, space telescopes are not affected by the Earths atmosphere but are diffraction limited. For example, the Hubble space telescope can reach a size of stars down to about 0. 1″
Arcsecond
–
Comparison of angular diameter of the Sun, Moon, planets and the International Space Station. To get a true representation of the sizes, view the image at a distance of 103 times the width of the "Moon: max." circle. For example, if this circle is 10 cm wide on your monitor, view it from 10.3 m away.
20.
Hour angle
–
In astronomy and celestial navigation, the hour angle is one of the coordinates used in the equatorial coordinate system to give the direction of a point on the celestial sphere. The hour angle of a point is the angle between two planes, one containing the Earths axis and the zenith, and the containing the Earths axis. The angle may be expressed as negative east of the plane and positive west of the meridian plane. The angle may be measured in degrees or in time, with 24h = 360° exactly, in astronomy, hour angle is defined as the angular distance on the celestial sphere measured westward along the celestial equator from the meridian to the hour circle passing through a point. It may be given in degrees, time, or rotations depending on the application, in celestial navigation, the convention is to measure in degrees westward from the prime meridian, from the local meridian or from the first point of Aries. The hour angle is paired with the declination to fully specify the location of a point on the sphere in the equatorial coordinate system. These angles can be measured in time or in degrees — one or the other, negative hour angles indicate the time until the next transit across the meridian, an hour angle of zero means the object is on the meridian. Observing the sun from earth, the hour angle is an expression of time, expressed in angular measurement, usually degrees. At solar noon the hour angle is 0.000 degree, with the time before solar noon expressed as negative degrees, for example, at 10,30 AM local apparent time the hour angle is -22. 5°. The cosine of the angle is used to calculate the solar zenith angle. The sidereal hour angle of a body on the sphere is its angular distance west of the vernal equinox generally measured in degrees. The SHA of a star changes slowly, and the SHA of a planet doesnt change very quickly, SHA is often used in celestial navigation and navigational astronomy. Sidereal hour angle + right ascension = 360° Clock position
Hour angle
–
As seen from above the
Earth 's
north pole, a star's local hour angle (LHA) for an observer near New York (red). Also depicted are the star's
right ascension and Greenwich hour angle (GHA), the
local mean sidereal time (LMST) and
Greenwich mean sidereal time (GMST). The symbol ʏ identifies the
vernal equinox direction.
21.
Star
–
It is primarily present in steroid-producing cells, including theca cells and luteal cells in the ovary, Leydig cells in the testis and cell types in the adrenal cortex. The aqueous phase between two membranes cannot be crossed by the lipophilic cholesterol, unless certain proteins assist in this process. It is now clear that this process is mediated by the action of StAR. The mechanism by which StAR causes cholesterol movement remains unclear as it appears to act from the outside of the mitochondria, some involve StAR transferring cholesterol itself like a shuttle. Another notion is that it causes cholesterol to be kicked out of the membrane to the inner. StAR may also promote the formation of contact sites between the outer and inner mitochondrial membranes to allow cholesterol influx, another suggests that StAR acts in conjunction with PBR, causing the movement of Cl− out of the mitochondria to facilitate contact site formation. However, evidence for an interaction between StAR and PBR remains elusive, in humans, the gene for StAR is located on chromosome 8p11.2 and the protein has 285 amino acids. The signal sequence of StAR that targets it to the mitochondria is clipped off in two steps with import into the mitochondria, phosphorylation at the serine at position 195 increases its activity. The domain of StAR important for promoting cholesterol transfer is the StAR-related transfer domain, StAR is the prototypic member of the START domain family of proteins and is thus also known as STARD1 for START domain-containing protein 1. It is hypothesized that the START domain forms a pocket in StAR that binds single cholesterol molecules for delivery to P450scc, the closest homolog to StAR is MLN64. Together they comprise the StarD1/D3 subfamily of START domain-containing proteins, StAR is a mitochondrial protein that is rapidly synthesized in response to stimulation of the cell to produce steroid. Hormones that stimulate its production depend on the type and include luteinizing hormone, ACTH. At the cellular level, StAR is synthesized typically in response to activation of the second messenger system. StAR has thus far found in all tissues that can produce steroids, including the adrenal cortex, the gonads, the brain. One known exception is the human placenta, mutations in the gene for StAR cause lipoid congenital adrenal hyperplasia, in which patients produce little steroid and can die shortly after birth. Mutations that less severely affect the function of StAR result in nonclassic lipoid CAH or familial glucocorticoid deficiency type 3, all known mutations disrupt StAR function by altering its START domain. In the case of StAR mutation, the phenotype does not present until birth since human placental steroidogenesis is independent of StAR. At the cellular level, the lack of StAR results in an accumulation of lipid within cells
Star
22.
Meridian (astronomy)
–
In astronomy, the meridian is the great circle passing through the celestial poles, the zenith, and the nadir of an observers location. Consequently, it also the horizons north and south points. A celestial meridian matches the projection of a terrestrial meridian onto the celestial sphere, hence, the number of astronomical meridians are infinite. There are several ways in which the meridian can be divided into semicircles, in one way, it is divided into the local meridian and the antimeridian. The former semicircle contains the zenith and is terminated by the celestial poles, in the horizontal coordinate system the meridian is divided into halves terminated by the horizons north and south points. The upper meridian passes through the zenith, and the lower meridian, a celestial object will appear to drift past the local meridian as the Earth spins, for the meridian is fixed to the local horizon. At culmination, the object reaches its highest point in the sky when crossing, or transiting, using an objects right ascension and the local sidereal time it is possible to determine the time of its culmination. The term meridian comes from the Latin meridies, which means both midday and south, meridian Prime meridian Longitude Millar, William. The Amateur Astronomers Introduction to the Celestial Sphere
Meridian (astronomy)
–
The meridian on the celestial sphere. The yellow hemi-disk is bounded above by the upper meridian.
23.
Sidereal time
–
Sidereal time /saɪˈdɪəriəl/ is a time-keeping system that astronomers use to locate celestial objects. Using sidereal time it is possible to point a telescope to the proper coordinates in the night sky. Briefly, sidereal time is a scale that is based on Earths rate of rotation measured relative to the fixed stars rather than the Sun. From a given point, a star found at one location in the sky will be found at the same location on another night at the same sidereal time. This is similar to how the time kept by a sundial can be used to find the location of the Sun, just as the Sun and Moon appear to rise in the east and set in the west due to the rotation of Earth, so do the stars. Both solar time and sidereal time make use of the regularity of Earths rotation about its polar axis, a mean sidereal day is 23 hours,56 minutes,4.0916 seconds, the time it takes Earth to make one rotation relative to the vernal equinox. The longer true sidereal period is called a day by the International Earth Rotation. It is also referred to as the period of rotation. Maps of the stars in the night sky use declination and right ascension as coordinates and these correspond to latitude and longitude respectively. In the sky, the meridian is the north to south line that goes through the point directly overhead. Solar time is measured by the apparent diurnal motion of the Sun, a mean solar day is the average time between local solar noons. Earth makes one rotation around its axis in a sidereal day, so after a sidereal day has passed, Earth still needs to rotate slightly more before the Sun reaches local noon according to solar time. A mean solar day is, therefore, nearly 4 minutes longer than a sidereal day, the stars are so far away that Earths movement along its orbit makes nearly no difference to their apparent direction, and so they return to their highest point in a sidereal day. Another way to see this difference is to notice that, relative to the stars, therefore, there is one fewer solar day per year than there are sidereal days. This makes a sidereal day approximately 365. 24/366.24 times the length of the 24-hour solar day, Earths rotation is not a simple rotation around an axis that would always remain parallel to itself. Earths rotational axis itself rotates about an axis, orthogonal to Earths orbit. This phenomenon is called the precession of the equinoxes, because of this precession, the stars appear to move around Earth in a manner more complicated than a simple constant rotation. In this reference frame, Earths rotation is close to constant and it is also in this reference frame that the tropical year, the year related to Earths seasons, represents one orbit of Earth around the Sun
Sidereal time
–
Key concepts
Sidereal time
–
Sidereal time vs solar time. Above left: a distant star (the small red circle) and the Sun are at
culmination, on the local meridian. Centre: only the distant star is at culmination (a mean
sidereal day). Right: a few minutes later the Sun is on the local meridian again. A
solar day is complete.
24.
Celestial navigation
–
Celestial navigation uses sights, or angular measurements taken between a celestial body and the visible horizon. The sun is most commonly used, but navigators can also use the moon, Celestial navigation is the use of angular measurements between celestial bodies and the visible horizon to locate ones position on the globe, on land as well as at sea. At a given time, any celestial body is located directly over one point on the Earths surface. The latitude and longitude of that point is known as the celestial body’s geographic position, the measured angle between the celestial body and the visible horizon is directly related to the distance between the celestial bodys GP and the observers position. Sights on two celestial bodies give two such lines on the chart, intersecting at the observers position, most navigators will use sights of three to five stars, if theyre available, since that will result in only one common intersection and minimize the chance for error. That premise is the basis for the most commonly used method of celestial navigation, there are several other methods of celestial navigation which will also provide position finding using sextant observations, such as the noon sight, and the more archaic lunar distance method. Joshua Slocum used the lunar distance method during the first ever recorded single-handed circumnavigation of the world, unlike the altitude-intercept method, the noon sight and lunar distance methods do not require accurate knowledge of time. An example illustrating the concept behind the method for determining one’s position is shown to the right. In the adjacent image, the two circles on the map represent lines of position for the Sun and Moon at 1200 GMT on October 29,2005. At this time, a navigator on a ship at sea measured the Moon to be 56 degrees above the horizon using a sextant, ten minutes later, the Sun was observed to be 40 degrees above the horizon. Lines of position were calculated and plotted for each of these observations. Since both the Sun and Moon were observed at their respective angles from the location, the navigator would have to be located at one of the two locations where the circles cross. In this case the navigator is either located on the Atlantic Ocean, about 350 nautical miles west of Madeira, or in South America, about 90 nautical miles southwest of Asunción, Paraguay. In most cases, determining which of the two intersections is the one is obvious to the observer because they are often thousands of miles apart. As it is unlikely that the ship is sailing across South America, note that the lines of position in the figure are distorted because of the map’s projection, they would be circular if plotted on a globe. Accurate angle measurement evolved over the years, one simple method is to hold the hand above the horizon with ones arm stretched out. The need for accurate measurements led to the development of a number of increasingly accurate instruments, including the kamal, astrolabe. Navigators measure distance on the globe in degrees, arcminutes and arcseconds, a nautical mile is defined as 1852 meters, but is also one minute of angle along a meridian on the Earth
Celestial navigation
–
A
sextant
25.
Minute of arc
–
A minute of arc, arcminute, arc minute, or minute arc is a unit of angular measurement equal to 1/60 of one degree. Since one degree is 1/360 of a turn, one minute of arc is 1/21600 of a turn, a second of arc, arcsecond, or arc second is 1/60 of an arcminute, 1/3600 of a degree, 1/1296000 of a turn, and π/648000 of a radian. To express even smaller angles, standard SI prefixes can be employed, the number of square arcminutes in a complete sphere is 4 π2 =466560000 π ≈148510660 square arcminutes. The standard symbol for marking the arcminute is the prime, though a single quote is used where only ASCII characters are permitted. One arcminute is thus written 1′ and it is also abbreviated as arcmin or amin or, less commonly, the prime with a circumflex over it. The standard symbol for the arcsecond is the prime, though a double quote is commonly used where only ASCII characters are permitted. One arcsecond is thus written 1″ and it is also abbreviated as arcsec or asec. In celestial navigation, seconds of arc are used in calculations. This notation has been carried over into marine GPS receivers, which normally display latitude and longitude in the format by default. An arcsecond is approximately the angle subtended by a U. S. dime coin at a distance of 4 kilometres, a milliarcsecond is about the size of a dime atop the Eiffel Tower as seen from New York City. A microarcsecond is about the size of a period at the end of a sentence in the Apollo mission manuals left on the Moon as seen from Earth, since antiquity the arcminute and arcsecond have been used in astronomy. The principal exception is Right ascension in equatorial coordinates, which is measured in units of hours, minutes. These small angles may also be written in milliarcseconds, or thousandths of an arcsecond, the unit of distance, the parsec, named from the parallax of one arcsecond, was developed for such parallax measurements. It is the distance at which the radius of the Earths orbit would subtend an angle of one arcsecond. The ESA astrometric space probe Gaia is hoped to measure star positions to 20 microarcseconds when it begins producing catalog positions sometime after 2016, there are about 1.3 trillion µas in a turn. Currently the best catalog positions of stars actually measured are in terms of milliarcseconds, apart from the Sun, the star with the largest angular diameter from Earth is R Doradus, a red supergiant with a diameter of 0.05 arcsecond. The dwarf planet Pluto has proven difficult to resolve because its angular diameter is about 0.1 arcsecond, space telescopes are not affected by the Earths atmosphere but are diffraction limited. For example, the Hubble space telescope can reach a size of stars down to about 0. 1″
Minute of arc
–
Comparison of angular diameter of the Sun, Moon, planets and the International Space Station. To get a true representation of the sizes, view the image at a distance of 103 times the width of the "Moon: max." circle. For example, if this circle is 10 cm wide on your monitor, view it from 10.3 m away.
26.
Second of arc
–
A minute of arc, arcminute, arc minute, or minute arc is a unit of angular measurement equal to 1/60 of one degree. Since one degree is 1/360 of a turn, one minute of arc is 1/21600 of a turn, a second of arc, arcsecond, or arc second is 1/60 of an arcminute, 1/3600 of a degree, 1/1296000 of a turn, and π/648000 of a radian. To express even smaller angles, standard SI prefixes can be employed, the number of square arcminutes in a complete sphere is 4 π2 =466560000 π ≈148510660 square arcminutes. The standard symbol for marking the arcminute is the prime, though a single quote is used where only ASCII characters are permitted. One arcminute is thus written 1′ and it is also abbreviated as arcmin or amin or, less commonly, the prime with a circumflex over it. The standard symbol for the arcsecond is the prime, though a double quote is commonly used where only ASCII characters are permitted. One arcsecond is thus written 1″ and it is also abbreviated as arcsec or asec. In celestial navigation, seconds of arc are used in calculations. This notation has been carried over into marine GPS receivers, which normally display latitude and longitude in the format by default. An arcsecond is approximately the angle subtended by a U. S. dime coin at a distance of 4 kilometres, a milliarcsecond is about the size of a dime atop the Eiffel Tower as seen from New York City. A microarcsecond is about the size of a period at the end of a sentence in the Apollo mission manuals left on the Moon as seen from Earth, since antiquity the arcminute and arcsecond have been used in astronomy. The principal exception is Right ascension in equatorial coordinates, which is measured in units of hours, minutes. These small angles may also be written in milliarcseconds, or thousandths of an arcsecond, the unit of distance, the parsec, named from the parallax of one arcsecond, was developed for such parallax measurements. It is the distance at which the radius of the Earths orbit would subtend an angle of one arcsecond. The ESA astrometric space probe Gaia is hoped to measure star positions to 20 microarcseconds when it begins producing catalog positions sometime after 2016, there are about 1.3 trillion µas in a turn. Currently the best catalog positions of stars actually measured are in terms of milliarcseconds, apart from the Sun, the star with the largest angular diameter from Earth is R Doradus, a red supergiant with a diameter of 0.05 arcsecond. The dwarf planet Pluto has proven difficult to resolve because its angular diameter is about 0.1 arcsecond, space telescopes are not affected by the Earths atmosphere but are diffraction limited. For example, the Hubble space telescope can reach a size of stars down to about 0. 1″
Second of arc
–
Comparison of angular diameter of the Sun, Moon, planets and the International Space Station. To get a true representation of the sizes, view the image at a distance of 103 times the width of the "Moon: max." circle. For example, if this circle is 10 cm wide on your monitor, view it from 10.3 m away.
27.
Axial precession
–
In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical bodys rotational axis. The term precession typically refers only to this largest part of the motion, other changes in the alignment of Earths axis—nutation and this term is still used in non-technical discussions, that is, when detailed mathematics are absent. Their combination was named general precession, instead of precession of the equinoxes, lunisolar precession is caused by the gravitational forces of the Moon and Sun on Earths equatorial bulge, causing Earths axis to move with respect to inertial space. Lunisolar precession is about 500 times greater than planetary precession, many references to the old terms exist in publications predating the change. Etymologically, precession and procession are both terms that relate to motion, Precession is derived from the Latin praecedere, to precede, to come before or earlier), while procession is derived from the Latin procedere, to march forward, to advance). Generally the term procession is used to describe a group of objects moving forward, the stars viewed from Earth are seen to proceed in a procession from east to west daily, due to the Earth’s diurnal motion, and yearly, due to the Earth’s revolution around the Sun. At the same time the stars can be observed to anticipate slightly such motion, at the rate of approximately 50 arc seconds per year, in describing this motion astronomers generally have shortened the term to simply precession. This issue is further obfuscated by the fact that many astronomers are physicists or astrophysicists, the precession of the Earths axis has a number of observable effects. First, the positions of the south and north celestial poles appear to move in circles against the backdrop of stars. Thus, while today the star Polaris lies approximately at the celestial pole, this will change over time. In approximately 3200 years, the star Gamma Cephei in the Cepheus constellation will succeed Polaris for this position, the south celestial pole currently lacks a bright star to mark its position, but over time precession also will cause bright stars to become south stars. As the celestial poles shift, there is a gradual shift in the apparent orientation of the whole star field. Secondly, the position of the Earth in its orbit around the Sun at the solstices, equinoxes, or other time defined relative to the seasons, slowly changes. For example, suppose that the Earths orbital position is marked at the summer solstice, in other words, the solstice occurred a little earlier in the orbit. Thus, the year, measuring the cycle of seasons, is about 20 minutes shorter than the sidereal year. For further details, see Changing pole stars and Polar shift and equinoxes shift, according to Ptolemys Almagest, Hipparchus measured the longitude of Spica and other bright stars. Comparing his measurements with data from his predecessors, Timocharis and Aristillus and he also compared the lengths of the tropical year and the sidereal year, and found a slight discrepancy. Virtually all of the writings of Hipparchus are lost, including his work on precession and they are mentioned by Ptolemy, who explains precession as the rotation of the celestial sphere around a motionless Earth
Axial precession
–
Precessional movement as seen from 'outside' the celestial sphere
Axial precession
–
Precessional movement of the Earth – the Earth rotates (white arrows) once a day about its axis of rotation (red); this axis itself rotates slowly (white circle), completing a rotation in approximately 26,000 years
28.
Polaris
–
Polaris, designated Alpha Ursae Minoris, commonly the North Star or Pole Star, is the brightest star in the constellation of Ursa Minor. It is very close to the celestial pole, making it the current northern pole star. The revised Hipparcos parallax gives a distance to Polaris of about 433 light-years, Polaris is a multiple star, comprising the main star in orbit with a smaller companion, the pair in orbit with Polaris B. There were once thought to be two more distant components—Polaris C and Polaris D—but these have been not to be physically associated with the Polaris system. Polaris Aa is a 4.5 solar mass F7 yellow supergiant of spectral type Ib and this is the first classical Cepheid to have a mass determined from its orbit. William Herschel discovered the star in 1780 while using a hand-built reflecting telescope, in 1929 it was discovered, by examining the spectrum of Polaris A, that it was a very close binary, with the secondary being a dwarf, which had been theorized in earlier observations. In January 2006, NASA released images, from the Hubble telescope, that showed the three members of the Polaris ternary system. The nearest dwarf star is in an orbit of only 18.5 au from Polaris A, about the distance between the Sun and Uranus), which explains why its light is swamped by its close and much brighter companion. Polaris A, the supergiant primary component, is a low-amplitude Population I classical Cepheid variable, cepheids constitute an important standard candle for determining distance, so Polaris, as the closest such star, is heavily studied. The variability of Polaris had been suspected since 1852, this variation was confirmed by Ejnar Hertzsprung in 1911, the range of brightness of Polaris during its pulsations is given as 1. 86–2.13, but the amplitude has changed since discovery. Prior to 1963, the amplitude was over 0.1 magnitude and was gradually decreasing. After 1966 it very rapidly decreased until it was less than 0.05 magnitude, since then and it has been reported that the amplitude is now increasing again, a reversal not seen in any other Cepheid. The period, roughly 4 days, has changed over time. It has steadily increased by around 4.5 seconds per year except for a hiatus in 1963–1965 and this was originally thought to be due to secular redward evolution across the Cepheid instability strip, but it may be due to interference between the primary and the first-overtone pulsation modes. Authors disagree on whether Polaris is a fundamental or first-overtone pulsator, the temperature of Polaris varies by only a small amount during its pulsations, but the amount of this variation is variable and unpredictable. The erratic changes of temperature and the amplitude of changes during each cycle, from less than 50 K to at least 170 K. Research reported in Science suggests that Polaris is 2.5 times brighter today than when Ptolemy observed it, because of its importance in celestial navigation, Polaris is known by numerous names. It became known as Polaris during the Renaissance, its derived from the Latin polaris of/near the pole
Polaris
–
Polaris as seen by the Hubble Space Telescope.
Polaris
–
This artist's concept shows three class F stars: supergiant Polaris A, dwarf Polaris Ab, and its distant dwarf companion, Polaris B
Polaris
–
A typical Northern Hemisphere star trail with Polaris in the center
Polaris
–
Ursa Major and Ursa Minor in relation to Polaris
29.
Draco (constellation)
–
Draco is a constellation in the far northern sky. Its name is Latin for dragon and it was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations today. The north pole of the ecliptic is in Draco, Draco is circumpolar, and can be seen all year from northern latitudes. Thuban was the pole star from 3942 BC, when it moved farther north than Theta Boötis. The Egyptian Pyramids were designed to have one side facing north, with an entrance passage geometrically aligned so that Thuban would be visible at night, due to the effects of precession, it will again be the pole star around the year AD21000. It is a giant star of magnitude 3.7,309 light-years from Earth. The traditional name of Alpha Draconis, Thuban, means head of the serpent, there are two other stars under magnitude 3 in Draco. The brighter of the two, and the brightest star in Draco, is Gamma Draconis, traditionally called Etamin or Eltanin and it is an orange giant star of magnitude 2.2,148 light-years from Earth. The aberration of starlight was discovered in 1728 when James Bradley observed Gamma Draconis, beta Draconis, traditionally called Rastaban, is a yellow giant star of magnitude 2.8,362 light-years from Earth. Its name shares a meaning with Thuban, head of the serpent, Draco is home to several double stars and binary stars. η Draconis is a star with a yellow-hued primary of magnitude 2.8. The two are separated by 4.8 arcseconds, mu Draconis, traditionally called Alrakis, is a binary star with two white components. Magnitude 5.6 and 5.7, the two orbit each other every 670 years. The Alrakis system is 88 light-years from Earth, nu Draconis is a similar binary star with two white components,100 light-years from Earth. Both components are of magnitude 4.9 and can be distinguished in an amateur telescope or a pair of binoculars. Omicron Draconis is a double star divisible in small telescopes, the primary is an orange giant of magnitude 4.6,322 light-years from Earth. The secondary is of magnitude 7.8, psi Draconis is a binary star divisible in binoculars and small amateur telescopes,72 light-years from Earth. The primary is a star of magnitude 4.6
Draco (constellation)
–
The constellation Draco as it can be seen by the naked eye.
Draco (constellation)
–
List of stars in Draco
Draco (constellation)
–
PGC 39058, a dwarf galaxy found within the Draco constellation – picture taken by ESA/Hubble & NASA.
Draco (constellation)
–
Draco coils around the north celestial pole, as depicted in Urania's Mirror, a set of constellation cards published in London c.1825
30.
Dorado
–
Dorado is a constellation in the southern sky. It was named in the late 16th century and is now one of the 88 modern constellations and its name refers to the dolphinfish, which is known as dorado in Portuguese, although it has also been depicted as a swordfish. Dorado contains most of the Large Magellanic Cloud, the remainder being in the constellation Mensa, the South Ecliptic pole also lies within this constellation. Its first depiction in an atlas was in Johann Bayers Uranometria of 1603 where it was also named Dorado. Dorado has been represented historically as a dolphinfish and a swordfish and it has also been represented as a goldfish. The constellation was known in the 17th and 18th century as Xiphias. The name Dorado ultimately become dominant and was adopted by the IAU, alpha Doradus is a blue-white star of magnitude 3.3,176 light-years from Earth. It is the brightest star in Dorado, Beta Doradus is a notably bright Cepheid variable star. It is a supergiant star that has a minimum magnitude of 4.1. One thousand and forty light-years from Earth, Beta Doradus has a period of 9 days and 20 hours, R Doradus is one of the many variable stars in Dorado. S Dor,9.721 hypergiant in the Large Magellanic Cloud, is the prototype of S Doradus variable stars, the variable star R Doradus 5.73 has the largest known apparent size of any star other than the Sun. Gamma Doradus is the prototype of the Gamma Doradus variable stars, supernova 1987A was the closest supernova to occur since the invention of the telescope. SNR 0509-67.5 is the remnant of an unusually energetic Type 1a supernova from about 400 years ago, HE 0437-5439 is a hypervelocity star escaping from the Milky Way/Magellanic Cloud system. Dorado is also the location of the South Ecliptic pole, which lies near the fishs head, the pole was called Polus Doradinalis by Willem Jansson Blaeu. Because Dorado contains part of the Large Magellanic Cloud, it is rich in deep sky objects, the Large Magellanic Cloud,1,000 light-years in diameter, is a satellite galaxy of the Milky Way Galaxy, located at a distance of 179,000 light-years. It has been deformed by its interactions with the larger Milky Way. In 1987, it became host to SN 1987A, the first supernova of 1987 and this 25, 000-light-year-wide galaxy contains over 10,000 million stars. All coordinates given are for Epoch J2000.0, NGC1566 is a face-on spiral galaxy
Dorado
–
The constellation Dorado as it can be seen by the naked eye.
Dorado
–
List of stars in Dorado
Dorado
–
NGC 1566 is an intermediate spiral galaxy.
Dorado
–
LEDA 89996 is a classic example of a spiral galaxy.
31.
Great circle
–
A great circle, also known as an orthodrome or Riemannian circle, of a sphere is the intersection of the sphere and a plane that passes through the center point of the sphere. This partial case of a circle of a sphere is opposed to a circle, the intersection of the sphere. Any diameter of any great circle coincides with a diameter of the sphere, and therefore all great circles have the same circumference as each other, a great circle is the largest circle that can be drawn on any given sphere. Every circle in Euclidean 3-space is a circle of exactly one sphere. For most pairs of points on the surface of a sphere, there is a great circle through the two points. The exception is a pair of points, for which there are infinitely many great circles. The minor arc of a circle between two points is the shortest surface-path between them. In this sense, the arc is analogous to “straight lines” in Euclidean geometry. The length of the arc of a great circle is taken as the distance between two points on a surface of a sphere in Riemannian geometry. The great circles are the geodesics of the sphere, in higher dimensions, the great circles on the n-sphere are the intersection of the n-sphere with 2-planes that pass through the origin in the Euclidean space Rn+1. To prove that the arc of a great circle is the shortest path connecting two points on the surface of a sphere, one can apply calculus of variations to it. Consider the class of all paths from a point p to another point q. Introduce spherical coordinates so that p coincides with the north pole. Any curve on the sphere that does not intersect either pole, except possibly at the endpoints, can be parametrized by θ = θ, ϕ = ϕ, a ≤ t ≤ b provided we allow φ to take on arbitrary real values. The infinitesimal arc length in these coordinates is d s = r θ ′2 + ϕ ′2 sin 2 θ d t. So the length of a curve γ from p to q is a functional of the curve given by S = r ∫ a b θ ′2 + ϕ ′2 sin 2 θ d t. Note that S is at least the length of the meridian from p to q, S ≥ r ∫ a b | θ ′ | d t ≥ r | θ − θ |. Since the starting point and ending point are fixed, S is minimized if and only if φ =0, so the curve must lie on a meridian of the sphere φ = φ0 = constant
Great circle
–
A great circle divides the sphere in two equal hemispheres
32.
Hipparchus
–
Hipparchus of Nicaea was a Greek astronomer, geographer, and mathematician. He is considered the founder of trigonometry but is most famous for his discovery of precession of the equinoxes. Hipparchus was born in Nicaea, Bithynia, and probably died on the island of Rhodes and he is known to have been a working astronomer at least from 162 to 127 BC. Hipparchus is considered the greatest ancient astronomical observer and, by some and he was the first whose quantitative and accurate models for the motion of the Sun and Moon survive. For this he made use of the observations and perhaps the mathematical techniques accumulated over centuries by the Babylonians. He developed trigonometry and constructed trigonometric tables, and he solved problems of spherical trigonometry. With his solar and lunar theories and his trigonometry, he may have been the first to develop a method to predict solar eclipses. Relatively little of Hipparchuss direct work survives into modern times, although he wrote at least fourteen books, only his commentary on the popular astronomical poem by Aratus was preserved by later copyists. There is a tradition that Hipparchus was born in Nicaea, in the ancient district of Bithynia. His birth date was calculated by Delambre based on clues in his work, Hipparchus must have lived some time after 127 BC because he analyzed and published his observations from that year. Hipparchus obtained information from Alexandria as well as Babylon, but it is not known when or if he visited these places and he is believed to have died on the island of Rhodes, where he seems to have spent most of his later life. It is not known what Hipparchuss economic means were nor how he supported his scientific activities and his appearance is likewise unknown, there are no contemporary portraits. In the 2nd and 3rd centuries coins were made in his honour in Bithynia that bear his name and show him with a globe, this supports the tradition that he was born there. As an astronomer of antiquity his influence, supported by ideas from Aristotle, held sway for nearly 2000 years, Hipparchuss only preserved work is Τῶν Ἀράτου καὶ Εὐδόξου φαινομένων ἐξήγησις. This is a critical commentary in the form of two books on a popular poem by Aratus based on the work by Eudoxus. Hipparchus also made a list of his works, which apparently mentioned about fourteen books. His famous star catalog was incorporated into the one by Ptolemy, the first trigonometric table was apparently compiled by Hipparchus, who is now consequently known as the father of trigonometry. There are a variety of mis-steps in the more ambitious 2005 paper, According to one book review, both of these claims have been rejected by other scholars
Hipparchus
–
Hipparchus as he appears in "
The School of Athens " by
Raphael.
33.
Star catalog
–
A star catalogue or star catalog, is an astronomical catalogue that lists stars. In astronomy, many stars are referred to simply by catalogue numbers, there are a great many different star catalogues which have been produced for different purposes over the years, and this article covers only some of the more frequently quoted ones. Star catalogues were compiled by many different ancient peoples, including the Babylonians, Greeks, Chinese, Persians, most modern catalogues are available in electronic format and can be freely downloaded from space agencies data center. Completeness and accuracy is described by the weakest apparent magnitude V, from their existing records, it is known that the ancient Egyptians recorded the names of only a few identifiable constellations and a list of thirty-six decans that were used as a star clock. They are better known by their Assyrian-era name Three Stars Each and these star catalogues, written on clay tablets, listed thirty-six stars, twelve for Anu along the celestial equator, twelve for Ea south of that, and twelve for Enlil to the north. In Ancient Greece, the astronomer and mathematician Eudoxus laid down a set of the classical constellations around 370 BC. His catalogue Phaenomena, rewritten by Aratus of Soli between 275 and 250 BC as a poem, became one of the most consulted astronomical texts in antiquity. It contains descriptions of the positions of the stars, the shapes of the constellations, approximately in the 3rd century BC, the Greek astronomers Timocharis of Alexandria and Aristillus created another star catalogue. Hipparchus completed his star catalogue in 129 BC, which he compared to Timocharis and this led him to determine the first value of the precession of the equinoxes. In the 2nd century, Ptolemy of Roman Egypt published a star catalogue as part of his Almagest, ptolemys catalogue was based almost entirely on an earlier one by Hipparchus. It remained the star catalogue in the Western and Arab worlds for over eight centuries. The earliest known inscriptions for Chinese star names were written on oracle bones, sources dating from the Zhou Dynasty which provide star names include the Zuo Zhuan, the Shi Jing, and the Canon of Yao in the Book of Documents. The Lüshi Chunqiu written by the Qin statesman Lü Buwei provides most of the names for the twenty-eight mansions, an earlier lacquerware chest found in the Tomb of Marquis Yi of Zeng contains a complete list of the names of the twenty-eight mansions. Star catalogues are traditionally attributed to Shi Shen and Gan De, the Shi Shen astronomy is attributed to Shi Shen, and the Astronomic star observation to Gan De. It was not until the Han Dynasty that astronomers started to observe and record names for all the stars that were apparent in the night sky, not just those around the ecliptic. A star catalogue is featured in one of the chapters of the late 2nd-century-BC history work Records of the Grand Historian by Sima Qian and contains the schools of Shi Shen and Gan Des work. For his Spiritual Constitution of the Universe of 120 AD, the astronomer Zhang Heng compiled a star catalogue comprising 124 constellations, Chinese constellation names were later adopted by the Koreans and Japanese. A large number of star catalogues were published by Muslim astronomers in the medieval Islamic world and these were mainly Zij treatises, including Arzachels Tables of Toledo, the Maragheh observatorys Zij-i Ilkhani and Ulugh Begs Zij-i-Sultani
Star catalog
–
An illustration of the constellation
Perseus (after
Perseus from
Greek mythology) from the star catalogue published by the German astronomer
Johannes Hevelius in 1690
34.
Ecliptic coordinate system
–
The ecliptic coordinate system is a celestial coordinate system commonly used for representing the positions and orbits of Solar System objects. Because most planets, and many small Solar System bodies have orbits with small inclinations to the ecliptic, using it as the fundamental plane is convenient. The systems origin can be either the center of the Sun or the center of the Earth, its direction is towards the vernal equinox. It may be implemented in spherical coordinates or rectangular coordinates, a slow motion of Earths axis, precession, causes a slow, continuous turning of the coordinate system westward about the poles of the ecliptic, completing one circuit in about 26,000 years. Superimposed on this is a motion of the ecliptic. The three most commonly used are, Mean equinox of an epoch is a fixed standard direction. Mean equinox of date is the intersection of the ecliptic of date with the mean equator, commonly used in planetary orbit calculation. True equinox of date is the intersection of the ecliptic of date with the true equator and this is the actual intersection of the two planes at any particular moment, with all motions accounted for. A position in the coordinate system is thus typically specified true equinox and ecliptic of date, mean equinox and ecliptic of J2000.0. Note that there is no mean ecliptic, as the ecliptic is not subject to small periodic oscillations, ecliptic longitude or celestial longitude measures the angular distance of an object along the ecliptic from the primary direction. Like right ascension in the coordinate system, the primary direction points from the Earth towards the Sun at the vernal equinox of the Northern Hemisphere. Because it is a system, ecliptic longitude is measured positive eastwards in the fundamental plane from 0° to 360°. Because of axial precession, the longitude of most fixed stars increases by about 50.3 arcseconds per year, or 83.8 arcminutes per century. Ecliptic latitude or celestial latitude, measures the distance of an object from the ecliptic towards the north or south ecliptic pole. For example, the ecliptic pole has a celestial latitude of +90°. Ecliptic latitude for fixed stars is not affected by precession, distance is also necessary for a complete spherical position. Different distance units are used for different objects, within the Solar System, astronomical units are used, and for objects near the Earth, Earth radii or kilometers are used. From antiquity through the 18th century, ecliptic longitude was measured using twelve zodiacal signs, each of 30° longitude
Ecliptic coordinate system
–
Earth-centered ecliptic coordinates as seen from outside the
celestial sphere. Ecliptic longitude (red) is measured along the
ecliptic from the vernal
equinox. Ecliptic latitude (yellow) is measured perpendicular to the ecliptic. A full globe is shown here, although high-latitude coordinates are seldom seen except for certain
comets and
asteroids.
35.
Telescope
–
A telescope is an optical instrument that aids in the observation of remote objects by collecting electromagnetic radiation. The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s and they found use in both terrestrial applications and astronomy. Within a few decades, the telescope was invented, which used mirrors to collect. In the 20th century many new types of telescopes were invented, including radio telescopes in the 1930s, the word telescope now refers to a wide range of instruments capable of detecting different regions of the electromagnetic spectrum, and in some cases other types of detectors. The word telescope was coined in 1611 by the Greek mathematician Giovanni Demisiani for one of Galileo Galileis instruments presented at a banquet at the Accademia dei Lincei, in the Starry Messenger, Galileo had used the term perspicillum. The earliest recorded working telescopes were the telescopes that appeared in the Netherlands in 1608. Their development is credited to three individuals, Hans Lippershey and Zacharias Janssen, who were spectacle makers in Middelburg, Galileo heard about the Dutch telescope in June 1609, built his own within a month, and improved upon the design in the following year. Also in 1609, Thomas Harriot became the first person known to point a telescope skyward in order to make observations of a celestial object. The idea that the objective, or light-gathering element, could be a mirror instead of a lens was being investigated soon after the invention of the refracting telescope. The potential advantages of using parabolic mirrors—reduction of spherical aberration and no chromatic aberration—led to many proposed designs, in 1668, Isaac Newton built the first practical reflecting telescope, of a design which now bears his name, the Newtonian reflector. The invention of the lens in 1733 partially corrected color aberrations present in the simple lens and enabled the construction of shorter. The largest reflecting telescopes currently have objectives larger than 10 m, the 20th century also saw the development of telescopes that worked in a wide range of wavelengths from radio to gamma-rays. The first purpose built radio telescope went into operation in 1937, since then, a tremendous variety of complex astronomical instruments have been developed. The name telescope covers a range of instruments. Most detect electromagnetic radiation, but there are differences in how astronomers must go about collecting light in different frequency bands. The near-infrared can be collected much like light, however in the far-infrared and submillimetre range. For example, the James Clerk Maxwell Telescope observes from wavelengths from 3 μm to 2000 μm, on the other hand, the Spitzer Space Telescope, observing from about 3 μm to 180 μm uses a mirror. Also using reflecting optics, the Hubble Space Telescope with Wide Field Camera 3 can observe in the range from about 0.2 μm to 1.7 μm
Telescope
–
The 100 inch (2.54 m) Hooker
reflecting telescope at
Mount Wilson Observatory near Los Angeles, USA.
Telescope
–
Modern telescopes typically use
CCDs instead of film for recording images. This is the sensor array in the
Kepler spacecraft.
Telescope
–
28-inch telescope and 40-foot telescope in
Greenwich in 2015.
Telescope
–
50 cm refracting telescope at
Nice Observatory.
36.
Equatorial mount
–
An equatorial mount is a mount for instruments that compensate the rotation of earth by having one rotational axis parallel to the Earths axis of rotation. This type of mount is used for astronomical telescopes and cameras, such an arrangement is called a sidereal drive. In astronomical telescope mounts, the axis is paired with a second perpendicular axis of motion. They may also be equipped with setting circles to allow for the location of objects by their celestial coordinates, equatorial mounts differ from mechanically simpler altazimuth mounts, which require variable speed motion around both axes to track a fixed object in the sky. Equatorial telescope mounts come in many designs, in the last twenty years motorized tracking has increasingly been supplemented with computerized object location. Digital setting circles take a computer with an object database that is attached to encoders. The computer monitors the telescopes position in the sky, the operator must push the telescope. Go-to systems use servo motors and the operator need not touch the instrument at all to change its position in the sky. The computers in these systems are typically either hand-held in a paddle or supplied through an adjacent laptop computer which is also used to capture images from an electronic camera. The electronics of modern telescope systems often include a port for autoguiding, a special instrument tracks a star and makes adjustment in the telescopes position while photographing the sky. To do so the autoguider must be able to issue commands through the control system. These commands can compensate for very slight errors in the tracking performance, in new observatory designs, equatorial mounts have been out of favor for decades in large-scale professional applications. Massive new instruments are most stable when mounted in an alt-azimuth configuration, computerized tracking and field-derotation are not difficult to implement at the professional level. At the amateur level, however, equatorial mounts remain popular, in the German equatorial mount, the primary structure is a T-shape, where the lower bar is the right ascension axis, and the upper bar is the declination axis. The telescope is placed on one end of the axis. The right ascension axis has bearings below the T-joint, that is, the Open Fork mount has a Fork attached to a right ascension axis at its base. The telescope is attached to two points at the other end of the fork so it can swing in declination. Most modern mass-produced catadioptric reflecting telescopes tend to be of this type, the mount resembles an Altazimuth mount, but with the azimuth axis tilted and lined up to match earth rotation axis with a piece of hardware usually called a wedge
Equatorial mount
–
A large German Equatorial Mount on the Forststernwarte Jena 50cm
Cassegrain reflector telescope.
Equatorial mount
–
German equatorial mount
Equatorial mount
–
Open fork mount
Equatorial mount
–
English mount on the
Hooker telescope
37.
Setting circles
–
Setting circles are used on telescopes equipped with an equatorial mount to find astronomical objects in the sky by their equatorial coordinates often used in star charts or ephemerides. Setting circles consist of two graduated disks attached to the ascension and declination axis of an equatorial mount. The right ascension disk is graduated into hours, minutes, the declination disk is graduated into degrees, minutes, and seconds. Since right ascension coordinates are fixed to the sphere the RA disk is usually driven by a clock mechanism in sync with sidereal time. Locating an object on the sphere with setting circles is similar to finding a location on a terrestrial map using latitude and longitude. Sometimes the right ascension setting circle has two scales on it, one for the Northern and one for the Southern hemisphere, historically setting circles have rivaled the telescopes optics as far as difficulty in construction. Making a set of setting circles required a lot of precision crafting on a dividing engine, setting circles usually had a large diameter and when combined with a vernier scale could point a telescope to nearly an arc minute of accuracy. In the 20th century setting circles were replaced with electronic encoders on most research telescopes, Polaris is roughly at the north pole, while Sigma Octantis is roughly at the south pole. Setting Right Ascension - After polar alignment, the uses a calculator or a known star to synchronize the right ascension circle with Sidereal Time. Accuracy of pointing the telescope can be hard to achieve and these sources of error add up and cause the telescope to point far from the desired object. They are also hard to control, for example, Polaris is often used as the north pole for alignment purposes. Also, even the finest graduations on setting circles are more than a degree apart. Nothing can be if the optical tube is not perpendicular to the declination axis or if the R. A. and Dec axes are not perpendicular. In the southern hemisphere the Right Ascension scale operates in reverse from in the Northern Hemisphere, the term Right Ascension took its name from early northern hemisphere observers for whom ascending stars were on the east or right hand side. In the southern hemisphere the east is on the left when a mount is aligned on the south pole. Many Right Ascension setting circles therefore carry two sets of numbers, one showing the value if the telescope is aligned in the northern hemisphere, the other for the southern. Alternatively, it is possible to point to a star very close to the object, rotate the circles to match the stars coordinates. Digital setting circles consist of two rotary encoders on both axis of the mount and a digital readout
Setting circles
–
Setting circles on an
equatorial fork-mounted
telescope
38.
John Flamsteed
–
John Flamsteed FRS was an English astronomer and the first Astronomer Royal. Flamsteed was born in Denby, Derbyshire, England, the son of Stephen Flamsteed and his first wife. He was educated at the school of Derby, and was educated at Derby School, in St Peters Churchyard, Derby. At that time, most masters of the school were Puritans, Flamsteed had a solid knowledge of Latin, essential for reading the scientific literature of the day, and a love of history, leaving the school in May,1662. His progress to Jesus College, Cambridge, recommended by the Master of Derby School, was delayed by years of chronic ill health. During those years, Flamsteed gave his father some help in his business, and from his father learnt arithmetic and the use of fractions, developing a keen interest in mathematics and astronomy. In July 1662, he was fascinated by the work of Johannes de Sacrobosco, De sphaera mundi. Early in 1663, he read Thomas Fales The Art of Dialling, in the summer of 1663, he read Wingates Canon, William Oughtreds Canon, and Thomas Stirrups Art of Dialling. At about the time, he acquired Thomas Streets Astronomia Carolina. Flamsteed was greatly impressed by the work of Horrocks, in September 1670, Flamsteed visited Cambridge and entered his name as an undergraduate at Jesus College. While it seems he never took up residence, he was there for two months in 1674, and had the opportunity to hear Isaac Newtons Lucasian Lectures. Ordained a deacon, he was preparing to take up a living in Derbyshire when he was invited to London by his patron Jonas Moore, Moore had recently made an offer to the Royal Society to pay for the establishment of an observatory. Charles appointed a Royal Commission to examine the proposal in December 1674, consisting of Lord Brouncker, Seth Ward, Samuel Moreland, Christopher Wren, Silius Titus, John Pell and Robert Hooke. Having arrived in London on 2 February 1675, and staying with Jonas Moore at the Tower of London and he was subsequently admitted as an official Assistant to the Royal Commission and supplied observations in order to test St Pierres proposal and to offer his own comments. On 4 March 1675 Flamsteed was appointed by royal warrant The Kings Astronomical Observator — the first English Astronomer Royal, in June 1675, another royal warrant provided for the founding of the Royal Greenwich Observatory, and Flamsteed laid the foundation stone on 10 August. He held that office, as well as that of Astronomer Royal and he is buried at Burstow, and the east window in the church was dedicated to him as a memorial. The will of Flamsteed’s widow, Margaret, left instructions for her own remains to be deposited “in the same Grave in which Mr John Flamsteed is buryed in the Chancell of Burstow Church. It seems no such monument was created, and almost 200 years later, after his death, his papers and scientific instruments were taken by his widow
John Flamsteed
–
John Flamsteed by
Godfrey Kneller, 1702
John Flamsteed
–
Memorial marking grave of John Flamsteed and his wife in the Chancel of St Bartholomew, Burstow
John Flamsteed
–
Bust of John Flamsteed in the Museum of the Royal Greenwich Observatory
39.
Historia Coelestis Britannica
–
John Flamsteed FRS was an English astronomer and the first Astronomer Royal. Flamsteed was born in Denby, Derbyshire, England, the son of Stephen Flamsteed and his first wife. He was educated at the school of Derby, and was educated at Derby School, in St Peters Churchyard, Derby. At that time, most masters of the school were Puritans, Flamsteed had a solid knowledge of Latin, essential for reading the scientific literature of the day, and a love of history, leaving the school in May,1662. His progress to Jesus College, Cambridge, recommended by the Master of Derby School, was delayed by years of chronic ill health. During those years, Flamsteed gave his father some help in his business, and from his father learnt arithmetic and the use of fractions, developing a keen interest in mathematics and astronomy. In July 1662, he was fascinated by the work of Johannes de Sacrobosco, De sphaera mundi. Early in 1663, he read Thomas Fales The Art of Dialling, in the summer of 1663, he read Wingates Canon, William Oughtreds Canon, and Thomas Stirrups Art of Dialling. At about the time, he acquired Thomas Streets Astronomia Carolina. Flamsteed was greatly impressed by the work of Horrocks, in September 1670, Flamsteed visited Cambridge and entered his name as an undergraduate at Jesus College. While it seems he never took up residence, he was there for two months in 1674, and had the opportunity to hear Isaac Newtons Lucasian Lectures. Ordained a deacon, he was preparing to take up a living in Derbyshire when he was invited to London by his patron Jonas Moore, Moore had recently made an offer to the Royal Society to pay for the establishment of an observatory. Charles appointed a Royal Commission to examine the proposal in December 1674, consisting of Lord Brouncker, Seth Ward, Samuel Moreland, Christopher Wren, Silius Titus, John Pell and Robert Hooke. Having arrived in London on 2 February 1675, and staying with Jonas Moore at the Tower of London and he was subsequently admitted as an official Assistant to the Royal Commission and supplied observations in order to test St Pierres proposal and to offer his own comments. On 4 March 1675 Flamsteed was appointed by royal warrant The Kings Astronomical Observator — the first English Astronomer Royal, in June 1675, another royal warrant provided for the founding of the Royal Greenwich Observatory, and Flamsteed laid the foundation stone on 10 August. He held that office, as well as that of Astronomer Royal and he is buried at Burstow, and the east window in the church was dedicated to him as a memorial. The will of Flamsteed’s widow, Margaret, left instructions for her own remains to be deposited “in the same Grave in which Mr John Flamsteed is buryed in the Chancell of Burstow Church. It seems no such monument was created, and almost 200 years later, after his death, his papers and scientific instruments were taken by his widow
Historia Coelestis Britannica
–
John Flamsteed by
Godfrey Kneller, 1702
Historia Coelestis Britannica
–
Memorial marking grave of John Flamsteed and his wife in the Chancel of St Bartholomew, Burstow
Historia Coelestis Britannica
–
Bust of John Flamsteed in the Museum of the Royal Greenwich Observatory
40.
Equinoctial colure
–
Colure, in astronomy, is either of the two principal meridians of the celestial sphere. The equinoctial colure is the meridian or great circle of the sphere which passes through the celestial poles. The solstitial colure is the meridian or great circle of the sphere which passes through the poles. There are several stars closely aligned with the solstitial colure, Pi, Beta, Delta Aurigae and this makes the solstitial colure point towards the North Celestial Pole and Polaris. Celestial coordinate system Ecliptic Celestial sphere Right ascension Equinox Solstice Harley, John Brian, Woodward, cartography in the Traditional Islamic and South Asian Societies. Geminus, Evans, James, Berggren, J. L. Geminoss Introduction to the phenomena, the Secret Architecture of our Nations Capital
Equinoctial colure
–
Orange = equinoctial colure Blue = solstitial colure
41.
Geographic coordinates
–
A geographic coordinate system is a coordinate system used in geography that enables every location on Earth to be specified by a set of numbers, letters or symbols. The coordinates are chosen such that one of the numbers represents a vertical position. A common choice of coordinates is latitude, longitude and elevation, to specify a location on a two-dimensional map requires a map projection. The invention of a coordinate system is generally credited to Eratosthenes of Cyrene. Ptolemy credited him with the adoption of longitude and latitude. Ptolemys 2nd-century Geography used the prime meridian but measured latitude from the equator instead. Mathematical cartography resumed in Europe following Maximus Planudes recovery of Ptolemys text a little before 1300, in 1884, the United States hosted the International Meridian Conference, attended by representatives from twenty-five nations. Twenty-two of them agreed to adopt the longitude of the Royal Observatory in Greenwich, the Dominican Republic voted against the motion, while France and Brazil abstained. France adopted Greenwich Mean Time in place of local determinations by the Paris Observatory in 1911, the latitude of a point on Earths surface is the angle between the equatorial plane and the straight line that passes through that point and through the center of the Earth. Lines joining points of the same latitude trace circles on the surface of Earth called parallels, as they are parallel to the equator, the north pole is 90° N, the south pole is 90° S. The 0° parallel of latitude is designated the equator, the plane of all geographic coordinate systems. The equator divides the globe into Northern and Southern Hemispheres, the longitude of a point on Earths surface is the angle east or west of a reference meridian to another meridian that passes through that point. All meridians are halves of great ellipses, which converge at the north and south poles, the prime meridian determines the proper Eastern and Western Hemispheres, although maps often divide these hemispheres further west in order to keep the Old World on a single side. The antipodal meridian of Greenwich is both 180°W and 180°E, the combination of these two components specifies the position of any location on the surface of Earth, without consideration of altitude or depth. The grid formed by lines of latitude and longitude is known as a graticule, the origin/zero point of this system is located in the Gulf of Guinea about 625 km south of Tema, Ghana. To completely specify a location of a feature on, in, or above Earth. Earth is not a sphere, but a shape approximating a biaxial ellipsoid. It is nearly spherical, but has an equatorial bulge making the radius at the equator about 0. 3% larger than the radius measured through the poles, the shorter axis approximately coincides with the axis of rotation
Geographic coordinates
–
Longitude lines are perpendicular and latitude lines are parallel to the equator.
42.
North Celestial Pole
–
The north and south celestial poles are the two imaginary points in the sky where the Earths axis of rotation, indefinitely extended, intersects the celestial sphere. The north and south celestial poles appear permanently directly overhead to an observer at the Earths North Pole and South Pole respectively. As the Earth spins on its axis, the two celestial poles remain fixed in the sky, and all other points appear to rotate around them, completing one circuit per day. The celestial poles are also the poles of the equatorial coordinate system, meaning they have declinations of +90 degrees. The celestial poles do not remain permanently fixed against the background of the stars, because of a phenomenon known as the precession of the equinoxes, the poles trace out circles on the celestial sphere, with a period of about 25,700 years. The Earths axis is subject to other complex motions which cause the celestial poles to shift slightly over cycles of varying lengths, see nutation, polar motion. Finally, over long periods the positions of the stars themselves change. An analogous concept applies to other planets, a planets celestial poles are the points in the sky where the projection of the axis of rotation intersects the celestial sphere. These points vary because different planets axes are oriented differently, Celestial bodies other than Earth also have similarly defined celestial poles. The north celestial pole currently is within a degree of the bright star Polaris, Polaris can, of course, only be seen from locations in the northern hemisphere. Polaris is near the pole for only a small fraction of the 25. It will remain a good approximation for about 1,000 years, to find Polaris, face north and locate the Big Dipper and Little Dipper asterisms. Looking at the cup part of the Big Dipper, imagine that the two stars at the edge of the cup form a line pointing upward out of the cup. This line points directly at the star at the tip of the Little Dippers handle and that star is Polaris, the North Star. The south celestial pole is only from the southern hemisphere. It lies in the dim constellation Octans, the Octant, sigma Octantis is identified as the south pole star, over a degree away from the pole, but with a magnitude of 5.5 it is barely visible on a clear night. The south celestial pole can be located from the Southern Cross, draw an imaginary line from γ Crucis to α Crucis—the two stars at the extreme ends of the long axis of the cross—and follow this line through the sky. This point is 5 or 6 degrees from the celestial pole
North Celestial Pole
–
Over the course of an evening, stars appear to rotate about the north celestial pole. Polaris, within a degree of the pole, is the single nearly-stationary star just to the right of the center of this image.
North Celestial Pole
–
The north and south celestial poles and their relation to
axis of rotation,
plane of orbit and
axial tilt.
North Celestial Pole
–
Celestial South Pole over the
Very Large Telescope.
North Celestial Pole
–
Locating the south celestial pole
43.
South Celestial Pole
–
Pole star or polar star is a name of Polaris in the constellation Ursa Minor, after its property of being the naked-eye star closest to the Earths celestial north pole. Indeed, the name Polaris, introduced in the 18th century, is shortened from New Latin stella polaris, the south celestial pole lacks a bright star like Polaris to mark its position. At present, the star nearest to the celestial south pole is the faint Sigma Octantis. In a more general sense, a star may be any fixed star close to either celestial pole of any given planetary body. It might refer to any star in the Earths remote history or future. The identity of the stars gradually changes over time because the celestial poles exhibit a slow continuous drift through the star field. The primary reason for this is the precession of the Earths rotational axis, precession causes the celestial poles to trace out circles on the celestial sphere approximately once every 26,000 years, passing close to different stars at different times. In classical antiquity, Beta Ursae Minoris was closer to the north pole than Alpha Ursae Minoris. The ancient name of Ursa Minor, anglicized as cynosure, has itself become a term for guiding principle after the constellations use in navigation. α Ursae Minoris was described as ἀειφανής always visible by Stobaeus in the 5th century and it was known as scip-steorra in 10th-century Anglo-Saxon England, reflecting its use in navigation. Nicolaus Lucensis published a collection of Marian poetry under the title Cynosura seu Mariana Stella Polaris in 1655, the name stella polaris was coined in the Renaissance, even though at that time it was still several degrees away from the celestial pole. Gemma Frisius determined this distance as 3°7 in the year 1547, in the Hindu Puranas, the north star is personified under the name of Dhruva. As of October 2012, Polaris had the declination +89°19′8″, the celestial pole will be nearest Polaris in 2100 and will thereafter become more distant. Due to the precession of the equinoxes, the role of North Star has passed from one star to another in the remote past, in 3000 BCE, the faint star Thuban in the constellation Draco was the North Star. At magnitude 3.67 it is only one-fifth as bright as Polaris, in the Roman era, the celestial pole was about equally distant from α Ursae Minoris and β Ursae Minoris. The precession of the equinoxes takes about 25,770 years to complete a cycle, Polaris mean position will reach a maximum declination of +89°3223, which translates to 1657 from the celestial north pole, in February 2102. Its maximum apparent declination will be +89°3250.62, which is 1629 from the north pole. Gamma Cephei will become closer to the celestial pole than Polaris around 3000 CE
South Celestial Pole
–
A French "navisphere": a type of celestial globe formerly used for navigation at sea
South Celestial Pole
–
A
long exposure (45 min.) photo of Polaris and
neighbouring stars, taken at Ehrenbürg (
Franconia), 2001.
44.
International Standard Book Number
–
The International Standard Book Number is a unique numeric commercial book identifier. An ISBN is assigned to each edition and variation of a book, for example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, the method of assigning an ISBN is nation-based and varies from country to country, often depending on how large the publishing industry is within a country. The initial ISBN configuration of recognition was generated in 1967 based upon the 9-digit Standard Book Numbering created in 1966, the 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108. Occasionally, a book may appear without a printed ISBN if it is printed privately or the author does not follow the usual ISBN procedure, however, this can be rectified later. Another identifier, the International Standard Serial Number, identifies periodical publications such as magazines, the ISBN configuration of recognition was generated in 1967 in the United Kingdom by David Whitaker and in 1968 in the US by Emery Koltay. The 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108, the United Kingdom continued to use the 9-digit SBN code until 1974. The ISO on-line facility only refers back to 1978, an SBN may be converted to an ISBN by prefixing the digit 0. For example, the edition of Mr. J. G. Reeder Returns, published by Hodder in 1965, has SBN340013818 -340 indicating the publisher,01381 their serial number. This can be converted to ISBN 0-340-01381-8, the check digit does not need to be re-calculated, since 1 January 2007, ISBNs have contained 13 digits, a format that is compatible with Bookland European Article Number EAN-13s. An ISBN is assigned to each edition and variation of a book, for example, an ebook, a paperback, and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, a 13-digit ISBN can be separated into its parts, and when this is done it is customary to separate the parts with hyphens or spaces. Separating the parts of a 10-digit ISBN is also done with either hyphens or spaces, figuring out how to correctly separate a given ISBN number is complicated, because most of the parts do not use a fixed number of digits. ISBN issuance is country-specific, in that ISBNs are issued by the ISBN registration agency that is responsible for country or territory regardless of the publication language. Some ISBN registration agencies are based in national libraries or within ministries of culture, in other cases, the ISBN registration service is provided by organisations such as bibliographic data providers that are not government funded. In Canada, ISBNs are issued at no cost with the purpose of encouraging Canadian culture. In the United Kingdom, United States, and some countries, where the service is provided by non-government-funded organisations. Australia, ISBNs are issued by the library services agency Thorpe-Bowker
International Standard Book Number
–
A 13-digit ISBN, 978-3-16-148410-0, as represented by an
EAN-13 bar code
45.
Brady Haran
–
Haran is also the co-host of the Hello Internet podcast along with fellow Youtuber CGP Grey. Brady Haran studied journalism for a year before being hired by The Adelaide Advertiser, in 2002, he moved from Australia to Nottingham, United Kingdom. In Nottingham, he worked for the BBC, began to work with film, in 2007, Haran worked as a filmmaker-in-residence for Nottingham Science City, as part of an agreement between the BBC and The University of Nottingham. Haran then left the BBC to work full-time making YouTube videos, following Test Tube, Haran decided to create new YouTube channels. In his first 5 years as an independent filmmaker he made over 1500 videos, in 2012, he was the producer, editor, and interviewer behind 12 YouTube channels such as The Periodic Table of Videos, Sixty Symbols and Numberphile. Working with Poliakoff, Harans videos explaining chemistry and science for non-technical persons received positive recognition, together, they have made over 500 short videos that cover the elements and other chemistry-related topics. Their YouTube channel has had more than 120 million views and their Gold Bullion Vault, shot in the vaults of The Bank of England, was released 7 December 2012, and received more than two million hits in the next two months. Also, Haran and Poliakoff authored an article in the Nature Chemistry journal, Haran frequently collaborates with professionals and experts, who often appear in his videos to discuss subjects relevant to their work. Most notably his series Periodic Videos features chemist Sir Martyn Poliakoff, séquin, scientists Brian Butterworth, Ed Copeland, Laurence Eaves, and Clifford Stoll, and scientific writers and popularizers Alex Bellos, Steve Mould, Matt Parker, Tom Scott, and Simon Singh. In January 2014, Haran launched the podcast Hello Internet along with co-host CGP Grey, the podcast peaked as the No.1 iTunes podcast in United Kingdom, United States, Germany, Canada, and Australia. It was selected as one of Apples best new podcasts of 2014, Grey reported a podcast listenership of approximately a quarter million downloads per episode as of September 2015. The podcast features discussions pertaining to their lives as professional content creators for YouTube, as well as their interests, typical topics include new gadgets, technology etiquette, workplace efficiency, wristwatches, plane accidents, vexillology, and the differences between Harans and Greys personal mannerisms. As a result of their conversations, Haran has been credited for coining the term freebooting to refer to the unauthorized rehosting of online media, the podcast has an official flag called Nail & Gear which was chosen by the listeners. Test tube, behind the scenes in the world of science, teaching chem eng – Martyn Poliakoff and Brady Haran on Nottingham Unis periodic table for the YouTube generation. How to measure the impact of chemistry on the small screen
Brady Haran
–
Haran at the
Dead Sea, 2013
46.
University of Nottingham
–
The University of Nottingham is a public research university based in Nottingham, Nottinghamshire, England, United Kingdom. It was founded as University College Nottingham in 1881, and was granted a Royal Charter in 1948, Nottinghams main campus and teaching hospital are situated on the outskirts of the City of Nottingham, with a number of smaller campuses and sites located elsewhere in Nottinghamshire and Derbyshire. Outside the United Kingdom, the University has campuses in Semenyih, Malaysia and Ningbo, Nottingham is organised into five constituent faculties, within which there are more than 50 schools, departments, institutes and research centres. Nottingham has about 44,000 students and 9,000 staff, for 2009 entry, the University was ranked 5th in England in terms of the absolute number of students and 15th for the proportion of students who achieved AAB+ at A-level. In 2011, the University was listed as one of 12 elite institutions that accommodated the top achieving students in England, the 2014 High Fliers survey stated that Nottingham was the most targeted university by the UKs top employers between 2013-14. In 2012, Nottingham was ranked 13th in the world in terms of the number of alumni listed among CEOs of the Fortune Global 500 and it is also ranked 2nd in the 2012 Summer Olympics table of British medal winners. Moreover, in 2015, Nottingham was listed as the 9th largest European producer of entrepreneurs, in the 2011 and 2014 GreenMetric World University Rankings, University Park was ranked as the worlds most sustainable campus. The institutions alumni have been awarded a variety of accolades, including 3 Nobel Prizes, a Turner Prize. In 1881, there were four professors – of Literature, Physics, Chemistry, the university college underwent significant expansion in the 1920s, when it moved from the centre of Nottingham to a large campus on the citys outskirts. The original University College building on Shakespeare Street in central Nottingham, known as the Arkwright Building, built it most grand and cakeily out of the noble loot derived from shrewd cash-chemistry by good Sir Jesse Boot. During this period of development, Nottingham attracted high-profile lecturers, including Albert Einstein, H. G. Wells, the blackboard used by Einstein during his time at Nottingham is still on display in the Physics department. Apart from its physical transfer to surroundings that could not be different from its original home. The Department of Slavonic Languages was established in 1933, the teaching of Russian having been introduced in 1916, however, further advances were delayed by the outbreak of war in 1939. University College Nottingham students received their degrees from the University of London, however, in 1948, the University was granted its Royal Charter, which endowed it with university status and gave it the power to confer degrees in its own name as The University of Nottingham. In 1970, the university established the UKs first new school of the 20th century. In 1999, Jubilee Campus was opened on the site of the Raleigh Bicycle Company. Nottingham then began to expand overseas, opening campuses in Malaysia, in 2005, the Kings Meadow Campus opened near University Park. The University has used several logos throughout its history, beginning with its coat of arms, later, Nottingham adopted a simpler logo, in which a stylised version of Nottingham Castle was surrounded by the text The University of Nottingham
University of Nottingham
–
University College Nottingham in 1897; the building is now known as the Arkwright Building and is part of
Nottingham Trent University
University of Nottingham
–
Art students from
Goldsmith's College at University College Nottingham in 1944
University of Nottingham
–
Trent Building – Originally housed the entire university when it moved to University Park in 1928
University of Nottingham
–
Jubilee Campus in 2012. On the left is the Sir Harry and Lady Djanogly Learning Resource Centre, a library which has the form of an inverted cone.
