1.
Comet
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A comet is an icy small Solar System body that, when passing close to the Sun, warms and begins to evolve gasses, a process called outgassing. This produces an atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred metres to tens of kilometres across and are composed of collections of ice, dust. The coma may be up to 15 times the Earths diameter, if sufficiently bright, a comet may be seen from the Earth without the aid of a telescope and may subtend an arc of 30° across the sky. Comets have been observed and recorded since ancient times by many cultures, Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star. Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars, hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space. The appearance of a comet is called an apparition, Comets are distinguished from asteroids by the presence of an extended, gravitationally unbound atmosphere surrounding their central nucleus. This atmosphere has parts termed the coma and the tail, however, extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids. Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System, the discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets. As of November 2014 there are 5,253 known comets, however, this represents only a tiny fraction of the total potential comet population, as the reservoir of comet-like bodies in the outer Solar System is estimated to be one trillion. Roughly one comet per year is visible to the eye, though many of those are faint. Particularly bright examples are called Great Comets, the word comet derives from the Old English cometa from the Latin comēta or comētēs. That, in turn, is a latinisation of the Greek κομήτης, Κομήτης was derived from κομᾶν, which was itself derived from κόμη and was used to mean the tail of a comet. The astronomical symbol for comets is ☄, consisting of a disc with three hairlike extensions. The solid, core structure of a comet is known as the nucleus, cometary nuclei are composed of an amalgamation of rock, dust, water ice, and frozen gases such as carbon dioxide, carbon monoxide, methane, and ammonia. As such, they are described as dirty snowballs after Fred Whipples model
2.
Apsis
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An apsis is an extreme point in an objects orbit. The word comes via Latin from Greek and is cognate with apse, for elliptic orbits about a larger body, there are two apsides, named with the prefixes peri- and ap-, or apo- added to a reference to the thing being orbited. For a body orbiting the Sun, the point of least distance is the perihelion, the terms become periastron and apastron when discussing orbits around other stars. For any satellite of Earth including the Moon the point of least distance is the perigee, for objects in Lunar orbit, the point of least distance is the pericynthion and the greatest distance the apocynthion. For any orbits around a center of mass, there are the terms pericenter and apocenter, periapsis and apoapsis are equivalent alternatives. A straight line connecting the pericenter and apocenter is the line of apsides and this is the major axis of the ellipse, its greatest diameter. For a two-body system the center of mass of the lies on this line at one of the two foci of the ellipse. When one body is larger than the other it may be taken to be at this focus. Historically, in systems, apsides were measured from the center of the Earth. In orbital mechanics, the apsis technically refers to the distance measured between the centers of mass of the central and orbiting body. However, in the case of spacecraft, the family of terms are used to refer to the orbital altitude of the spacecraft from the surface of the central body. The arithmetic mean of the two limiting distances is the length of the axis a. The geometric mean of the two distances is the length of the semi-minor axis b, the geometric mean of the two limiting speeds is −2 ε = μ a which is the speed of a body in a circular orbit whose radius is a. The words pericenter and apocenter are often seen, although periapsis/apoapsis are preferred in technical usage, various related terms are used for other celestial objects. The -gee, -helion and -astron and -galacticon forms are used in the astronomical literature when referring to the Earth, Sun, stars. The suffix -jove is occasionally used for Jupiter, while -saturnium has very rarely used in the last 50 years for Saturn. The -gee form is used as a generic closest approach to planet term instead of specifically applying to the Earth. During the Apollo program, the terms pericynthion and apocynthion were used when referring to the Moon, regarding black holes, the term peri/apomelasma was used by physicist Geoffrey A. Landis in 1998 before peri/aponigricon appeared in the scientific literature in 2002
3.
Semi-major and semi-minor axes
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In geometry, the major axis of an ellipse is its longest diameter, a line segment that runs through the center and both foci, with ends at the widest points of the perimeter. The semi-major axis is one half of the axis, and thus runs from the centre, through a focus. Essentially, it is the radius of an orbit at the two most distant points. For the special case of a circle, the axis is the radius. One can think of the axis as an ellipses long radius. The semi-major axis of a hyperbola is, depending on the convention, thus it is the distance from the center to either vertex of the hyperbola. A parabola can be obtained as the limit of a sequence of ellipses where one focus is fixed as the other is allowed to move arbitrarily far away in one direction. Thus a and b tend to infinity, a faster than b, the semi-minor axis is a line segment associated with most conic sections that is at right angles with the semi-major axis and has one end at the center of the conic section. It is one of the axes of symmetry for the curve, in an ellipse, the one, in a hyperbola. The semi-major axis is the value of the maximum and minimum distances r max and r min of the ellipse from a focus — that is. In astronomy these extreme points are called apsis, the semi-minor axis of an ellipse is the geometric mean of these distances, b = r max r min. The eccentricity of an ellipse is defined as e =1 − b 2 a 2 so r min = a, r max = a. Now consider the equation in polar coordinates, with one focus at the origin, the mean value of r = ℓ / and r = ℓ /, for θ = π and θ =0 is a = ℓ1 − e 2. In an ellipse, the axis is the geometric mean of the distance from the center to either focus. The semi-minor axis of an ellipse runs from the center of the ellipse to the edge of the ellipse, the semi-minor axis is half of the minor axis. The minor axis is the longest line segment perpendicular to the axis that connects two points on the ellipses edge. The semi-minor axis b is related to the axis a through the eccentricity e. A parabola can be obtained as the limit of a sequence of ellipses where one focus is fixed as the other is allowed to move arbitrarily far away in one direction
4.
Astronomical unit
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The astronomical unit is a unit of length, roughly the distance from Earth to the Sun. However, that varies as Earth orbits the Sun, from a maximum to a minimum. Originally conceived as the average of Earths aphelion and perihelion, it is now defined as exactly 149597870700 metres, the astronomical unit is used primarily as a convenient yardstick for measuring distances within the Solar System or around other stars. However, it is also a component in the definition of another unit of astronomical length. A variety of symbols and abbreviations have been in use for the astronomical unit. In a 1976 resolution, the International Astronomical Union used the symbol A for the astronomical unit, in 2006, the International Bureau of Weights and Measures recommended ua as the symbol for the unit. In 2012, the IAU, noting that various symbols are presently in use for the astronomical unit, in the 2014 revision of the SI Brochure, the BIPM used the unit symbol au. In ISO 80000-3, the symbol of the unit is ua. Earths orbit around the Sun is an ellipse, the semi-major axis of this ellipse is defined to be half of the straight line segment that joins the aphelion and perihelion. The centre of the sun lies on this line segment. In addition, it mapped out exactly the largest straight-line distance that Earth traverses over the course of a year, knowing Earths shift and a stars shift enabled the stars distance to be calculated. But all measurements are subject to some degree of error or uncertainty, improvements in precision have always been a key to improving astronomical understanding. Improving measurements were continually checked and cross-checked by means of our understanding of the laws of celestial mechanics, the expected positions and distances of objects at an established time are calculated from these laws, and assembled into a collection of data called an ephemeris. NASAs Jet Propulsion Laboratory provides one of several ephemeris computation services, in 1976, in order to establish a yet more precise measure for the astronomical unit, the IAU formally adopted a new definition. Equivalently, by definition, one AU is the radius of an unperturbed circular Newtonian orbit about the sun of a particle having infinitesimal mass. As with all measurements, these rely on measuring the time taken for photons to be reflected from an object. However, for precision the calculations require adjustment for such as the motions of the probe. In addition, the measurement of the time itself must be translated to a scale that accounts for relativistic time dilation
5.
Orbital eccentricity
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The orbital eccentricity of an astronomical object is a parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is an orbit, values between 0 and 1 form an elliptical orbit,1 is a parabolic escape orbit. The term derives its name from the parameters of conic sections and it is normally used for the isolated two-body problem, but extensions exist for objects following a rosette orbit through the galaxy. In a two-body problem with inverse-square-law force, every orbit is a Kepler orbit, the eccentricity of this Kepler orbit is a non-negative number that defines its shape. The limit case between an ellipse and a hyperbola, when e equals 1, is parabola, radial trajectories are classified as elliptic, parabolic, or hyperbolic based on the energy of the orbit, not the eccentricity. Radial orbits have zero angular momentum and hence eccentricity equal to one, keeping the energy constant and reducing the angular momentum, elliptic, parabolic, and hyperbolic orbits each tend to the corresponding type of radial trajectory while e tends to 1. For a repulsive force only the trajectory, including the radial version, is applicable. For elliptical orbits, a simple proof shows that arcsin yields the projection angle of a circle to an ellipse of eccentricity e. For example, to view the eccentricity of the planet Mercury, next, tilt any circular object by that angle and the apparent ellipse projected to your eye will be of that same eccentricity. From Medieval Latin eccentricus, derived from Greek ἔκκεντρος ekkentros out of the center, from ἐκ- ek-, eccentric first appeared in English in 1551, with the definition a circle in which the earth, sun. Five years later, in 1556, a form of the word was added. The eccentricity of an orbit can be calculated from the state vectors as the magnitude of the eccentricity vector, e = | e | where. For elliptical orbits it can also be calculated from the periapsis and apoapsis since rp = a and ra = a, where a is the semimajor axis. E = r a − r p r a + r p =1 −2 r a r p +1 where, rp is the radius at periapsis. For Earths annual orbit path, ra/rp ratio = longest_radius / shortest_radius ≈1.034 relative to center point of path, the eccentricity of the Earths orbit is currently about 0.0167, the Earths orbit is nearly circular. Venus and Neptune have even lower eccentricity, over hundreds of thousands of years, the eccentricity of the Earths orbit varies from nearly 0.0034 to almost 0.058 as a result of gravitational attractions among the planets. The table lists the values for all planets and dwarf planets, Mercury has the greatest orbital eccentricity of any planet in the Solar System. Such eccentricity is sufficient for Mercury to receive twice as much solar irradiation at perihelion compared to aphelion, before its demotion from planet status in 2006, Pluto was considered to be the planet with the most eccentric orbit
6.
Orbital inclination
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Orbital inclination measures the tilt of an objects orbit around a celestial body. It is expressed as the angle between a plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Earth directly above the equator, the plane of the orbit is the same as the Earths equatorial plane. The general case is that the orbit is tilted, it spends half an orbit over the northern hemisphere. If the orbit swung between 20° north latitude and 20° south latitude, then its orbital inclination would be 20°, the inclination is one of the six orbital elements describing the shape and orientation of a celestial orbit. It is the angle between the plane and the plane of reference, normally stated in degrees. For a satellite orbiting a planet, the plane of reference is usually the plane containing the planets equator, for planets in the Solar System, the plane of reference is usually the ecliptic, the plane in which the Earth orbits the Sun. This reference plane is most practical for Earth-based observers, therefore, Earths inclination is, by definition, zero. Inclination could instead be measured with respect to another plane, such as the Suns equator or the invariable plane, the inclination of orbits of natural or artificial satellites is measured relative to the equatorial plane of the body they orbit, if they orbit sufficiently closely. The equatorial plane is the perpendicular to the axis of rotation of the central body. An inclination of 30° could also be described using an angle of 150°, the convention is that the normal orbit is prograde, an orbit in the same direction as the planet rotates. Inclinations greater than 90° describe retrograde orbits, thus, An inclination of 0° means the orbiting body has a prograde orbit in the planets equatorial plane. An inclination greater than 0° and less than 90° also describe prograde orbits, an inclination of 63. 4° is often called a critical inclination, when describing artificial satellites orbiting the Earth, because they have zero apogee drift. An inclination of exactly 90° is an orbit, in which the spacecraft passes over the north and south poles of the planet. An inclination greater than 90° and less than 180° is a retrograde orbit, an inclination of exactly 180° is a retrograde equatorial orbit. For gas giants, the orbits of moons tend to be aligned with the giant planets equator, the inclination of exoplanets or members of multiple stars is the angle of the plane of the orbit relative to the plane perpendicular to the line-of-sight from Earth to the object. An inclination of 0° is an orbit, meaning the plane of its orbit is parallel to the sky. An inclination of 90° is an orbit, meaning the plane of its orbit is perpendicular to the sky
7.
Periodic comet
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Periodic comets are comets having orbital periods of less than 200 years or that have been observed during more than a single perihelion passage. Periodic comet is sometimes used to mean any comet with a periodic orbit. Periodic comets receive a permanent number prefix usually after the perihelion passage. In nearly all cases, comets are named after their discoverer, even so, quite a few comets were lost because their orbits are also affected by non-gravitational effects such as the release of gas and other material that forms the comets coma and tail. Unlike a long-period comet, the perihelion passage of a numbered periodic comet can be predicted with a high degree of accuracy. Periodic comets sometimes bear the same name repeatedly, the IAU system distinguishes between them either through the prefix or by the full designation. In the literature, a numbering system is applied to periodic comets, thus 181P and 192P are known as Comet Shoemaker–Levy 6 and Comet Shoemaker–Levy 1. Non-periodic Shoemaker–Levy comets are interleaved in this sequence, C/1991 B1 between 2 and 3, C/1991 T2 between 5 and 6, C/1993 K1 and C/1994 E2 after Shoemaker–Levy 9. In comet nomenclature, the letter before the / is either C, P, D, X, or A for an object that was identified as a comet. Some lists retain the C prefix for comets of periods larger than about 30 years until their return is confirmed
8.
Solar System
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The Solar System is the gravitationally bound system comprising the Sun and the objects that orbit it, either directly or indirectly. Of those objects that orbit the Sun directly, the largest eight are the planets, with the remainder being significantly smaller objects, such as dwarf planets, of the objects that orbit the Sun indirectly, the moons, two are larger than the smallest planet, Mercury. The Solar System formed 4.6 billion years ago from the collapse of a giant interstellar molecular cloud. The vast majority of the mass is in the Sun. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being composed of rock. The four outer planets are giant planets, being more massive than the terrestrials. All planets have almost circular orbits that lie within a flat disc called the ecliptic. The Solar System also contains smaller objects, the asteroid belt, which lies between the orbits of Mars and Jupiter, mostly contains objects composed, like the terrestrial planets, of rock and metal. Beyond Neptunes orbit lie the Kuiper belt and scattered disc, which are populations of trans-Neptunian objects composed mostly of ices, within these populations are several dozen to possibly tens of thousands of objects large enough that they have been rounded by their own gravity. Such objects are categorized as dwarf planets, identified dwarf planets include the asteroid Ceres and the trans-Neptunian objects Pluto and Eris. In addition to two regions, various other small-body populations, including comets, centaurs and interplanetary dust clouds. Six of the planets, at least four of the dwarf planets, each of the outer planets is encircled by planetary rings of dust and other small objects. The solar wind, a stream of charged particles flowing outwards from the Sun, the heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of the interstellar medium, it extends out to the edge of the scattered disc. The Oort cloud, which is thought to be the source for long-period comets, the Solar System is located in the Orion Arm,26,000 light-years from the center of the Milky Way. For most of history, humanity did not recognize or understand the concept of the Solar System, the invention of the telescope led to the discovery of further planets and moons. The principal component of the Solar System is the Sun, a G2 main-sequence star that contains 99. 86% of the known mass. The Suns four largest orbiting bodies, the giant planets, account for 99% of the mass, with Jupiter. The remaining objects of the Solar System together comprise less than 0. 002% of the Solar Systems total mass, most large objects in orbit around the Sun lie near the plane of Earths orbit, known as the ecliptic
9.
Edwin Holmes (astronomer)
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Edwin Alfred Holmes was an English amateur astronomer who is best remembered as the discoverer of Comet 17P/Holmes. Edwin Holmes was born in Sheffield, Yorkshire, in 1839 and he later moved to London where he worked as a seller of glass. He lived at Hornsey Rise in North London from where he observed with a 12-inch aperture reflecting telescope he had manufactured himself, Holmes was a regular contributor to the British Astronomical Association and to the magazine The English Mechanic and World of Science. He became well known for his letters to the English Mechanic, often criticising the opinions of other amateur astronomers. In particular, he argued for the use of reflecting telescopes in preference to refractors of similar cost, edwin Holmes discovered the periodic comet 17P/Holmes on 6 November 1892, and his discovery was confirmed within days at the Royal Observatory Greenwich. Holmes discovered the comet after it suddenly brightened, allowing him to notice it close in the sky to the great Andromeda Galaxy, the comet remained visible to the unaided eye for another three weeks until it faded away. 75 days later the comet once again brightened to naked-eye visibility, Holmes was later awarded the Donohoe Comet Medal of the Astronomical Society of the Pacific. He was appointed an associate of the Astronomical Society of Wales, a form of honorary membership
10.
Coma (cometary)
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The coma is the nebulous envelope around the nucleus of a comet, formed when the comet passes close to the Sun on its highly elliptical orbit, as the comet warms, parts of it sublimes. This gives a comet a fuzzy appearance when viewed in telescopes and distinguishes it from stars, the word coma comes from the Greek kome, which means hair and is the origin of the word comet itself. The coma is generally made of ice and comet dust, water dominates up to 90% of the volatiles that outflow from the nucleus when the comet is within 3-4 AU of the Sun. The parent molecule is destroyed primarily through photodissociation and to a smaller extent photoionization. The solar wind plays a role in the destruction of water compared to photochemistry. Larger dust particles are left along the orbital path while smaller particles are pushed away from the Sun into the comets tail by light pressure. Comas typically grow in size as comets approach the Sun, and they can be as large as the diameter of Jupiter, about a month after an outburst in October 2007, comet 17P/Holmes briefly had a tenuous dust atmosphere larger than the Sun. The Great Comet of 1811 also had a coma roughly the diameter of the Sun, even though the coma can become quite large, its size can actually decrease about the time it crosses the orbit of Mars around 1.5 AU from the Sun. At this distance the solar wind becomes strong enough to blow the gas and dust away from the coma, Comets were found to emit X-rays in late-March 1996. This surprised researchers, because X-ray emission is associated with very high-temperature bodies. This ripping off leads to the emission of X-rays and far ultraviolet photons, with basic Earth-surface based telescope and some technique, the size of the Coma can be calculated. Called the drift method, one locks the telescope in position and that time multiplied by the cosine of comets declination, times.25 should equal the comas diameter in arcminutes. If the distance to the comet is known, then the apparent size of the coma can be determined. In 2015, it was noted that the ALICE instrument on the ESA Rosetta spacecraft to comet 67/P, detected hydrogen, oxygen, carbon and nitrogen in the Coma, which they also called the Comets atmosphere. Alice is a spectrograph, and it found that electrons created by UV light were colliding and breaking up molecules of water. OAO-2 discovered large halos of hydrogen gas around comets, space probe Giotto detected hydrogen ions at distance of 7.8 million km away from Halley when it did close flyby of the comet in 1986. A hydrogen gas halo was detected to be 15 times the diameter of Sun and this triggered NASA to point the Pioneer Venus mission at the Comet, and it was determined that the Comet emitting 12 tons of water per second. The hydrogen gas emission has not been detected from Earths surface because those wavelengths are blocked by the atmosphere, the process by which water is broken down into hydrogen and oxygen was studied by the ALICE instrument aboard the Rosetta spacecraft
11.
Sun
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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
12.
Mass
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In physics, mass is a property of a physical body. It is the measure of a resistance to acceleration when a net force is applied. It also determines the strength of its gravitational attraction to other bodies. The basic SI unit of mass is the kilogram, Mass is not the same as weight, even though mass is often determined by measuring the objects weight using a spring scale, rather than comparing it directly with known masses. An object on the Moon would weigh less than it does on Earth because of the lower gravity and this is because weight is a force, while mass is the property that determines the strength of this force. In Newtonian physics, mass can be generalized as the amount of matter in an object, however, at very high speeds, special relativity postulates that energy is an additional source of mass. Thus, any body having mass has an equivalent amount of energy. In addition, matter is a defined term in science. There are several distinct phenomena which can be used to measure mass, active gravitational mass measures the gravitational force exerted by an object. Passive gravitational mass measures the force exerted on an object in a known gravitational field. The mass of an object determines its acceleration in the presence of an applied force, according to Newtons second law of motion, if a body of fixed mass m is subjected to a single force F, its acceleration a is given by F/m. A bodys mass also determines the degree to which it generates or is affected by a gravitational field and this is sometimes referred to as gravitational mass. The standard International System of Units unit of mass is the kilogram, the kilogram is 1000 grams, first defined in 1795 as one cubic decimeter of water at the melting point of ice. Then in 1889, the kilogram was redefined as the mass of the prototype kilogram. As of January 2013, there are proposals for redefining the kilogram yet again. In this context, the mass has units of eV/c2, the electronvolt and its multiples, such as the MeV, are commonly used in particle physics. The atomic mass unit is 1/12 of the mass of a carbon-12 atom, the atomic mass unit is convenient for expressing the masses of atoms and molecules. Outside the SI system, other units of mass include, the slug is an Imperial unit of mass, the pound is a unit of both mass and force, used mainly in the United States
13.
Andromeda Galaxy
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The Andromeda Galaxy, also known as Messier 31, M31, or NGC224, is a spiral galaxy approximately 780 kiloparsecs from Earth. It is the nearest major galaxy to the Milky Way and was referred to as the Great Andromeda Nebula in older texts. It received its name from the area of the sky in which it appears, the constellation of Andromeda, which was named after the mythological princess Andromeda. Andromeda is approximately 220,000 light years across, and it is the largest galaxy of the Local Group, which contains the Milky Way, the Triangulum Galaxy. The mass of the Andromeda Galaxy is estimated to be 1. 5×1012 solar masses, the Milky Way and Andromeda galaxies are expected to collide in 4.5 billion years, eventually merging to form a giant elliptical galaxy or perhaps a large disc galaxy. Around the year 964, the Persian astronomer Abd al-Rahman al-Sufi described the Andromeda Galaxy, star charts of that period labeled it as the Little Cloud. In 1612, the German astronomer Simon Marius gave a description of the Andromeda Galaxy based on telescopic observations. In 1764, Charles Messier catalogued Andromeda as object M31 and incorrectly credited Marius as the discoverer despite it being visible to the naked eye, in 1785, the astronomer William Herschel noted a faint reddish hue in the core region of Andromeda. In 1850, William Parsons, 3rd Earl of Rosse, saw, in 1864, William Huggins noted that the spectrum of Andromeda differs from a gaseous nebula. The spectra of Andromeda displays a continuum of frequencies, superimposed with dark lines that help identify the chemical composition of an object. Andromedas spectrum is similar to the spectra of individual stars. In 1885, a supernova was seen in Andromeda, the first, at the time Andromeda was considered to be a nearby object, so the cause was thought to be a much less luminous and unrelated event called a nova, and was named accordingly, Nova 1885. In 1887, Isaac Roberts took the first photographs of Andromeda, Roberts actually mistook Andromeda and similar spiral nebulae as solar systems being formed. In 1912, Vesto Slipher used spectroscopy to measure the velocity of Andromeda with respect to our solar system—the largest velocity yet measured. In 1917, Heber Curtis observed a nova within Andromeda, searching the photographic record,11 more novae were discovered. Curtis noticed that these novae were, on average,10 magnitudes fainter than those that occurred elsewhere in the sky, as a result, he was able to come up with a distance estimate of 500,000 light-years. He became a proponent of the island universes hypothesis, which held that spiral nebulae were actually independent galaxies. In 1920, the Great Debate between Harlow Shapley and Curtis took place, concerning the nature of the Milky Way, spiral nebulae, in 1922 Ernst Öpik presented a method to estimate the distance of Andromeda using the measured velocities of its stars
14.
Magnitude (astronomy)
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In astronomy, magnitude is a logarithmic measure of the brightness of an object, measured in a specific wavelength or passband, usually in the visible or near-infrared spectrum. An imprecise but systematic determination of the magnitude of objects was introduced in ancient times by Hipparchus, astronomers use two different definitions of magnitude, apparent magnitude and absolute magnitude. This distance is 10 parsecs for stars and 1 astronomical unit for planets, a minor planets size is typically estimated based on its absolute magnitude in combination with its presumed albedo. The brighter an object appears, the lower the value of its magnitude, with the brightest objects reaching negative values. The Sun has an apparent magnitude of −27, the full moon −13, the brightest planet Venus measures −5, and Sirius, an apparent magnitude can also be assigned to man-made objects in Earth orbit. The brightest satellite flares are ranked at −9, and the International Space Station, ISS, the scale is logarithmic, and defined such that each step of one magnitude changes the brightness by a factor of the fifth root of 100, or approximately 2.512. For example, a magnitude 1 star is exactly a hundred times brighter than a magnitude 6 star, the magnitude system dates back roughly 2000 years to the Greek astronomer Hipparchus who classified stars by their apparent brightness, which they saw as size. To the unaided eye, a prominent star such as Sirius or Arcturus appears larger than a less prominent star such as Mizar. For all the other Stars, which are seen by the Help of a Telescope. Note that the brighter the star, the smaller the magnitude, Bright first magnitude stars are 1st-class stars, the system was a simple delineation of stellar brightness into six distinct groups but made no allowance for the variations in brightness within a group. He concluded that first magnitude stars measured 2 arc minutes in apparent diameter, with second through sixth magnitude stars measuring 1 1⁄2′, 1 1⁄12′, 3⁄4′, 1⁄2′, the development of the telescope showed that these large sizes were illusory—stars appeared much smaller through the telescope. However, early telescopes produced a spurious disk-like image of a star that was larger for brighter stars, early photometric measurements demonstrated that first magnitude stars are about 100 times brighter than sixth magnitude stars. Thus in 1856 Norman Pogson of Oxford proposed that a scale of 5√100 ≈2.512 be adopted between magnitudes, so five magnitude steps corresponded precisely to a factor of 100 in brightness. Every interval of one magnitude equates to a variation in brightness of 5√100 or roughly 2.512 times. Consequently, a first magnitude star is about 2.5 times brighter than a second star,2.52 brighter than a third magnitude star,2.53 brighter than a fourth magnitude star. This is the modern system, which measures the brightness, not the apparent size. Using this logarithmic scale, it is possible for a star to be brighter than “first class”, so Arcturus or Vega are magnitude 0, and Sirius is magnitude −1.46. As mentioned above, the scale appears to work in reverse, the larger the negative value, the brighter
15.
Edward Walter Maunder
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Edward Walter Maunder was born in 1851, in London, the youngest child of a minister of the Wesleyan Society. He attended Kings College London but never graduated and he took a job in a London bank to finance his studies. In 1873 Maunder returned to the Royal Observatory, taking a position as a spectroscopic assistant, shortly after, in 1875, he married Edith Hannah Bustin, who gave birth to six children,3 sons,2 daughters and a son who died in infancy. She worked as a computer at the Observatory from 1890 to 1895. In 1895 Maunder and Russell married, in 1916 Annie Maunder became one of the first women accepted by the Royal Astronomical Society. After 1891, he was assisted in his work by his wife Annie Maunder, in 1904, he published their results in the form of the butterfly diagram. The period, recognised initially by Spörer, now bears the name Maunder minimum and he travelled extensively for observations going to places such as the West Indies, Lapland, India, Algiers, Mauritius. His last eclipse expedition was to Labrador for the Solar eclipse of 30 August 1905 at the invitation of the Canadian government. In 1882 Maunder observed what he called a beam, as yet unexplained. However, Maunder wrote that the phenomenon moved rapidly from horizon to horizon, further, upper tangent arc cannot occur during nighttime when the observation was made. Since he made his observation during highly intense auroral activity, he assumed it was some extraordinary auroral phenomenon and he observed Mars and was a sceptic of the notion of Martian canals. He conducted visual experiments using marked circular disks which led him to conclude, correctly, also he was convinced that there cannot be life as in our world on Mars, as there are no temperature-equating winds and too low mean temperatures. Craters on Mars and the Moon were named in his and his wife Annies honour, in 1890, Maunder was a driving force in the foundation of the British Astronomical Association. Maunder was the first editor of the Journal of the BAA and he was also director of its Mars Section 1892-1893, the Star Colour Section 1900-1901, President 1894-1896 and finally Solar Section director 1910-1925. His older brother, Thomas Frid Maunder, was a co-founder, the Indian Eclipse,1898, Report of the Expeditions Organized by the British Astronomical Association. London, Hazel, Watson, and Viney, Ld, the Royal Observatory, Greenwich—Original publication, London, The Religious Tract Society Maunder, E. Walter. Note on the Distribution of Sun-Spots in Heliographic Latitude, 1874–1902, monthly Notices of the Royal Astronomical Society. Maunder, E. Astronomy of the Bible, An Elementary Commentary on the Astronomical References in the Holy Scripture, astronomers of To-day and Their Work
16.
Royal Observatory, Greenwich
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The Royal Observatory, Greenwich is an observatory situated on a hill in Greenwich Park, overlooking the River Thames. It played a role in the history of astronomy and navigation. The observatory was commissioned in 1675 by King Charles II, with the stone being laid on 10 August. The site was chosen by Sir Christopher Wren and he appointed John Flamsteed as the first Astronomer Royal. The building was completed in the summer of 1676, the building was often called Flamsteed House, in reference to its first occupant. The scientific work of the observatory was relocated elsewhere in stages in the first half of the 20th century,1675 –22 June, Royal Observatory founded. 1675 –10 August, construction began,1714 Longitude Act established the Board of Longitude and Longitude rewards. The Astronomer Royal was, until the Board was dissolved in 1828,1767 Astronomer Royal Nevil Maskelyne began publication of the Nautical Almanac, based on observations made at the Observatory. 1833 Daily time signals began, marked by dropping a Time ball,1899 The New Physical Observatory was completed. 1924 Hourly time signals from the Royal Observatory were first broadcast on 5 February,1948 Office of the Astronomer Royal was moved to Herstmonceux. 1957 Royal Observatory completed its move to Herstmonceux, becoming the Royal Greenwich Observatory, the Greenwich site is renamed the Old Royal Observatory. Greenwich site is returned to its name, the Royal Observatory. The Ordnance Office was given responsibility for building the Observatory, with Moore providing the key instruments, Moore donated two clocks, built by Thomas Tompion, which were installed in the 20 foot high Octagon Room, the principal room of the building. They were of unusual design, each with a pendulum 13 feet in length mounted above the face, giving a period of four seconds. British astronomers have used the Royal Observatory as a basis for measurement. Four separate meridians have passed through the buildings, defined by successive instruments, subsequently, nations across the world used it as their standard for mapping and timekeeping. When the Airy circle became the reference for the meridian, the difference resulting from the change was considered enough to be neglected. When a new triangulation was done between 1936 and 1962, scientists determined that in the Ordnance Survey system the longitude of the international Greenwich meridian was not 0° and this old astronomical prime meridian has been replaced by a more precise prime meridian
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Greenwich
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Greenwich is an early-established district of todays London, England, centred 5.5 miles east south-east of Charing Cross. The town lends its name to the Royal Borough of Greenwich, Greenwich is generally described as being part of South-east London and sometimes as being part of East London. Greenwich is notable for its history and for giving its name to the Greenwich Meridian. The town became the site of a palace, the Palace of Placentia from the 15th century. The palace fell into disrepair during the English Civil War and was rebuilt as the Royal Naval Hospital for Sailors by Sir Christopher Wren and his assistant Nicholas Hawksmoor. These buildings became the Royal Naval College in 1873, and they remained an establishment for military education until 1998 when they passed into the hands of the Greenwich Foundation. The historic rooms within these buildings remain open to the public, other buildings are used by University of Greenwich and Trinity Laban Conservatoire of Music and Dance. The town became a resort in the 18th century and many grand houses were built there, such as Vanbrugh Castle established on Maze Hill. From the Georgian period estates of houses were constructed above the town centre, Greenwich formed part of Kent until 1889 when the County of London was created. The place-name Greenwich is first attested in a Saxon charter of 918 and it is recorded as Grenewic in 964, and as Grenawic in the Anglo-Saxon Chronicle for 1013. It is Grenviz in the Domesday Book of 1086, and Grenewych in the Taxatio Ecclesiastica of 1291, the name means green wic or settlement. An article in The Times of 13 October 1967 stated, East Greenwich, gateway to the Blackwall Tunnel, remains solidly working class, the manpower for one eighth of Londons heavy industry. West Greenwich is a hybrid, the spirit of Nelson, the Cutty Sark, the Maritime Museum, an industrial waterfront and a number of elegant houses, ripe for development. Royal charters granted to English colonists in North America, often used the name of the manor of East Greenwich for describing the tenure as that of free socage, New England charters provided that the grantees should hold their lands as of his Majesty’s manor of East Greenwich. Grants named the castle of Windsor, places in North America that have taken the name East Greenwich include a township in Gloucester County, New Jersey, a hamlet in Washington County, New York, and a town in Kent County, Rhode Island. Tumuli to the south-west of Flamsteed House, in Greenwich Park, are thought to be early Bronze Age barrows re-used by the Saxons in the 6th century as burial grounds, to the east between the Vanbrugh and Maze Hill Gates is the site of a Roman villa or temple. A small area of red paving tesserae protected by railings marks the spot and it was excavated in 1902 and 300 coins were found dating from the emperors Claudius and Honorius to the 5th century. This was excavated by the Channel 4 television programme Time Team in 1999, broadcast in 2000, the Roman road from London to Dover, Watling Street crossed the high ground to the south of Greenwich, through Blackheath
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England
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England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west, the Irish Sea lies northwest of England and the Celtic Sea lies to the southwest. England is separated from continental Europe by the North Sea to the east, the country covers five-eighths of the island of Great Britain in its centre and south, and includes over 100 smaller islands such as the Isles of Scilly, and the Isle of Wight. England became a state in the 10th century, and since the Age of Discovery. The Industrial Revolution began in 18th-century England, transforming its society into the worlds first industrialised nation, Englands terrain mostly comprises low hills and plains, especially in central and southern England. However, there are uplands in the north and in the southwest, the capital is London, which is the largest metropolitan area in both the United Kingdom and the European Union. In 1801, Great Britain was united with the Kingdom of Ireland through another Act of Union to become the United Kingdom of Great Britain and Ireland. In 1922 the Irish Free State seceded from the United Kingdom, leading to the latter being renamed the United Kingdom of Great Britain, the name England is derived from the Old English name Englaland, which means land of the Angles. The Angles were one of the Germanic tribes that settled in Great Britain during the Early Middle Ages, the Angles came from the Angeln peninsula in the Bay of Kiel area of the Baltic Sea. The earliest recorded use of the term, as Engla londe, is in the ninth century translation into Old English of Bedes Ecclesiastical History of the English People. According to the Oxford English Dictionary, its spelling was first used in 1538. The earliest attested reference to the Angles occurs in the 1st-century work by Tacitus, Germania, the etymology of the tribal name itself is disputed by scholars, it has been suggested that it derives from the shape of the Angeln peninsula, an angular shape. An alternative name for England is Albion, the name Albion originally referred to the entire island of Great Britain. The nominally earliest record of the name appears in the Aristotelian Corpus, specifically the 4th century BC De Mundo, in it are two very large islands called Britannia, these are Albion and Ierne. But modern scholarly consensus ascribes De Mundo not to Aristotle but to Pseudo-Aristotle, the word Albion or insula Albionum has two possible origins. Albion is now applied to England in a poetic capacity. Another romantic name for England is Loegria, related to the Welsh word for England, Lloegr, the earliest known evidence of human presence in the area now known as England was that of Homo antecessor, dating to approximately 780,000 years ago. The oldest proto-human bones discovered in England date from 500,000 years ago, Modern humans are known to have inhabited the area during the Upper Paleolithic period, though permanent settlements were only established within the last 6,000 years
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William Maw
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William Henry Maw was a British civil engineer and astronomer. Born into a family and orphaned at age 16, Maw was taken into the workshops of the Eastern Counties Railway as an assistant before progressing to the design office as a draughtsman. He was made the head of the office and designed the first outside cylinder locomotive for use in India, in 1865 he founded the journal Engineering and remained an editor for the rest of his life. He left the railway and became a consulting engineer his many works including printing presses for several newspapers and he was president of the Civil and Mechanical Engineers Society, the Institution of Mechanical Engineers and the Institution of Civil Engineers. Maw was also an astronomer and was a Fellow of the Royal Astronomical Society with a particular interest in double stars. He co-founded the British Astronomical Association for amateur astronomers and served as its treasurer and he later became a council member, treasurer and president of the RAS. During the First World War he served his country as a member for the Ministry of Munitions. Maw was born in Scarborough on 6 December 1838 into a family, his father was a captain of the Merchant Navy. He was privately educated at Sykes School in his hometown and it was there that he befriended Edward Harland who would later co-found the Harland and Wolff shipbuilding company. In 1853 his father was lost at sea, leaving the family without an income, his mother died shortly afterwards, in March 1855 he was taken on as an assistant first in the carriage and then the locomotive workshops of the Eastern Counties Railway at Stratford Works. During this period he studied drawing at the Mechanics Institute, later to become Birkbeck College and he was so talented at drawing that in 1859, at the age of 21, he was made head of the office. In 1865 he left Eastern Counties and, with Zerah Colburn and he would remain an editor of the journal for the rest of his life. He was made a fellow of the RAS on 14 December 1888 and he co-founded the British Astronomical Association, an amateur astronomy association, and served as its treasurer from 1890 to 1913 and its president from 1898 to 1900. In 1892 he was elected as a member of the council of the RAS, serving as treasurer from 1900 to 1905, Maw was created an honorary Doctor of Laws by the University of Glasgow in 1909 for his contributions to mechanical engineering. He served upon the board of the National Physical Laboratory and on committees for the Ministry of Munitions during the First World War. He died at home on 19 March 1924 and was survived by his wife, Maw from the Lick Observatory Records Digital Archive, UC Santa Cruz Librarys Digital Collections
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Kensington
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Kensington is an affluent district within the Royal Borough of Kensington and Chelsea in West London. Its commercial heart is Kensington High Street, the affluent and densely populated area contains the major museum district of South Kensington, which has the Royal Albert Hall for music and nearby Royal College of Music. The area is home to many of Londons European embassies, the first mention of the area is in the Domesday Book of 1086, where it was written in Latin as Chenesitone, which has been interpreted to have originally been Kenesignetun in Anglo-Saxon. A variation may be Kesyngton, in 1396 and he in turn granted the tenancy of Kensington to his vassal Aubrey de Vere I, who was holding the manor in 1086, according to Domesday Book. The bishops heir, Robert de Mowbray, rebelled against William Rufus, Aubrey de Vere I had his tenure converted to a tenancy in-chief, holding Kensington after 1095 directly of the crown. He granted land and church there to Abingdon Abbey at the deathbed request of his young eldest son, Geoffrey. As the Veres became the earls of Oxford, their estate at Kensington came to be known as Earls Court, while the Abingdon lands were called Abbots Kensington and the church St Mary Abbots. The original Kensington Barracks, built at Kensington Gate in the late 18th century, were demolished in 1858, the focus of the area is Kensington High Street, a busy commercial centre with many shops, typically upmarket. The street was declared Londons second best shopping street in February 2005 thanks to its range, however, since October 2008 the street has faced competition from the Westfield shopping centre in nearby White City. Kensingtons second group of buildings is at South Kensington, where several streets of small to medium-sized shops. This is also the end of Exhibition Road, the thoroughfare that serves the areas museums. To the west, a border is kept along the line of the Counter Creek marked by the West London railway line, in the north east, the large Royal Park of Kensington Gardens is a green buffer. The other main area in Kensington is Holland Park, just north of Kensington High Street. Kensington is, in general, an affluent area, a trait that it now shares with its neighbour to the south. In early 2007, houses sold in Upper Phillimore Gardens for in excess of £20 million, Kensington is also very densely populated, it forms part of the most densely populated local government district in the United Kingdom. This high density is not formed from high-rise buildings, instead, unlike northern extremities of the Borough, Kensington lacks high-rise buildings except for the Holiday Inns London Kensington Forum Hotel in Cromwell Road, which is a 27-storey building. The Olympia exhibition hall is just over the border in West Kensington. Kensington is part of the Royal Borough of Kensington and Chelsea, the head office of newspaper group DMGT is located in Northcliffe House in Kensington, which is the office part of the large Barkers building
. Bibcode:2009A&A...495..975A. doi:10.1051/0004-6361:200810458.
