1.
Lightcurve
–
In astronomy, a light curve is a graph of light intensity of a celestial object or region, as a function of time. The light is usually in a particular frequency interval or band, the study of the light curve, together with other observations, can yield considerable information about the physical process that produces it or constrain the physical theories about it. Light waves can also be used in botany to determine a plants reactions to light intensities, in astronomy, light curves from a supernova are used to determine what type of supernova it is. If the supernovas light curve has a maximum and slopes down gradually. If the supernovas light curve has a sharp maximum, slopes down quickly. In planetary science, a curve can be used to derive the rotation period of a minor planet, moon. Thus, astronomers measure the amount of produced by an object as a function of time. The time separation of peaks in the curve gives an estimate of the rotational period of the object. The difference between the maximum and minimum brightnesses can be due to the shape of the object, or to bright, for example, an asymmetrical asteroids light curve generally has more pronounced peaks, while a more spherical objects light curve will be flatter. The Asteroid Lightcurve Database of the Collaborative Asteroid Lightcurve Link uses a code to assess the quality of a period solution for minor planet light curves. Its quality code parameter U ranges from 0 to 3, U =0 → Result later proven incorrect U =1 → Result based on fragmentary light curve, U =2 → Result based on less than full coverage. Period may be wrong by 30 percent or ambiguous, U =3 → Secure result within the precision given. A trailing plus sign or minus sign is used to indicate a slightly better or worse quality than the unsigned value. In botany, a light curve shows the response of leaf tissue or algal communities to varying light intensities. Since photosynthesis is limited by ambient carbon dioxide levels, light curves are often repeated at several different constant carbon dioxide concentrations. The AAVSO online light curve generator can plot light curves for thousands of variable stars Lightcurves, An Introduction by NASAs Imagine the Universe
2.
James Craig Watson
–
James Craig Watson was a Canadian-American astronomer, discoverer of comets and minor planets, director of the Ann Arbor Observatory, and awarded with the Lalande Prize in 1869. He was born in the village of Fingal, Ontario Canada and his family relocated to Ann Arbor, Michigan in 1850. At age 15 he was matriculated at the University of Michigan and he graduated with a BA in 1857 and received a masters degree on examination after two years study in astronomy under professor Franz Brünnow. He became Professor of Physics and instructor in Mathematics, and in 1863, succeeded him as professor of Astronomy and he wrote the textbook Theoretical Astronomy in 1868. He discovered 22 asteroids, beginning with 79 Eurynome in 1863, one of his asteroid discoveries,139 Juewa was made in Beijing when Watson was there to observe the 1874 transit of Venus. The name Juewa was chosen by Chinese officials, another was 121 Hermione in 1872, from Ann Arbor, Michigan, and this asteroid was found to have a small asteroid moon in 2002. He was a member of the most important expeditions for astronomical observation sent out by the United States Government during his time. He was a believer in the existence of the planet Vulcan, a hypothetical planet closer to the Sun than Mercury. He believed he had seen such two such planets during his observation of the 1878 solar eclipse and he died of peritonitis at the age of only 42 and was buried at Forest Hill, Ann Arbor. He had amassed a considerable amount of money through non-astronomical business activities, by bequest he established the James Craig Watson Medal, awarded every two years by the National Academy of Sciences for contributions to astronomy. Watson won the Lalande Prize given by the French Academy of Sciences for 1869 and he was a member of the National Academy of Sciences and the American Philosophical Society. He received the degree of Doctor of Philosophy from the University of Leipzig in 1870, and from Yale College in 1871. The main-belt asteroid 729 Watsonia is named in his honour, as is the lunar crater Watson, in Search of Planet Vulcan, The Ghost in Newtons Clockwork Machine
3.
Aethra (Greek mythology)
–
In Greek mythology, Aethra or Aithra was a name applied to four different individuals, Aethra was a daughter of King Pittheus of Troezen and the mother of Theseus. Aegeus went to Troezen, a city southwest of Athens that had as its patrons Athena and Poseidon, following the instructions of Athena in a dream, she left the sleeping Aegeus and waded across to the island of Sphairia that lay close to Troezens shore. There she poured a libation to Sphairos, Pelops charioteer, and was raped by Poseidon in the night, when she was thus doubly pregnant, Aegeus decided to go back to Athens. Aethra did as she was told, and Theseus, recovering the weapons that were his birthright, grew to be a hero, killing the Minotaur. Later, when Theseus kidnapped Helen, he gave her to Aethra for safekeeping, helens brothers, the Dioscuri, took Helen back and kidnapped Aethra in revenge. She went to Troy with Helen and remained there until found by her grandson, Acamas, with significant alterations to the character, a version of this Aethra appears, a sorceress and concubine of Poseidon, in Richard Strausss famous opera Die ägyptische Helena. Aethra is also the name of one of the Oceanids, the 3000 daughters of Oceanus and she is sometimes called the wife of Atlas and mother of the Pleiades and the Hyades. A figure called Aethra is, in one source, called the wife of Hyperion, rather than Theia, and mother of Helios, Eos, another Aethra was the wife of the Spartan Phalanthus. She fulfilled the prophecy given to her husband by her tears, after which he conquered Tarentum for himself
4.
Minor planet
–
A minor planet is an astronomical object in direct orbit around the Sun that is neither a planet nor exclusively classified as a comet. Minor planets can be dwarf planets, asteroids, trojans, centaurs, Kuiper belt objects, as of 2016, the orbits of 709,706 minor planets were archived at the Minor Planet Center,469,275 of which had received permanent numbers. The first minor planet to be discovered was Ceres in 1801, the term minor planet has been used since the 19th century to describe these objects. The term planetoid has also used, especially for larger objects such as those the International Astronomical Union has called dwarf planets since 2006. Historically, the asteroid, minor planet, and planetoid have been more or less synonymous. This terminology has become complicated by the discovery of numerous minor planets beyond the orbit of Jupiter. A Minor planet seen releasing gas may be classified as a comet. Before 2006, the IAU had officially used the term minor planet, during its 2006 meeting, the IAU reclassified minor planets and comets into dwarf planets and small Solar System bodies. Objects are called dwarf planets if their self-gravity is sufficient to achieve hydrostatic equilibrium, all other minor planets and comets are called small Solar System bodies. The IAU stated that the minor planet may still be used. However, for purposes of numbering and naming, the distinction between minor planet and comet is still used. Hundreds of thousands of planets have been discovered within the Solar System. The Minor Planet Center has documented over 167 million observations and 729,626 minor planets, of these,20,570 have official names. As of March 2017, the lowest-numbered unnamed minor planet is 1974 FV1, as of March 2017, the highest-numbered named minor planet is 458063 Gustavomuler. There are various broad minor-planet populations, Asteroids, traditionally, most have been bodies in the inner Solar System. Near-Earth asteroids, those whose orbits take them inside the orbit of Mars. Further subclassification of these, based on distance, is used, Apohele asteroids orbit inside of Earths perihelion distance. Aten asteroids, those that have semi-major axes of less than Earths, Apollo asteroids are those asteroids with a semimajor axis greater than Earths, while having a perihelion distance of 1.017 AU or less. Like Aten asteroids, Apollo asteroids are Earth-crossers, amor asteroids are those near-Earth asteroids that approach the orbit of Earth from beyond, but do not cross it
5.
Mars crosser
–
A Mars-crosser is an asteroid whose orbit crosses that of Mars. The known numbered Mars-crossers are listed here and they include the two numbered Mars trojans 5261 Eureka and 1998 VF31. Many databases, for instance the JPL Small-Body Database, only list asteroids with a greater than 1.3 AU as Mars-crossers. An asteroid with a less than this is classed as a near-Earth object even though it is crossing the orbit of Mars as well as crossing that of Earth. Nevertheless, these objects are listed on this page, a grazer is an object with a perihelion below the aphelion of Mars but above the Martian perihelion. The JPL SBDB lists 13,500 Mars-crossing asteroids, only 18 MCAs are brighter than absolute magnitude 12.5, which typically makes these asteroids with H<12.5 more than 13 km in diameter depending on the albedo. The smallest known MCAs have a magnitude of around 24 and are typically less than 100 meters in diameter. Instead, they are categorized as Near Earth Objects
6.
Perihelion and aphelion
–
The perihelion is the point in the orbit of a celestial body where it is nearest to its orbital focus, generally a star. It is the opposite of aphelion, which is the point in the orbit where the body is farthest from its focus. The word perihelion stems from the Ancient Greek words peri, meaning around or surrounding, aphelion derives from the preposition apo, meaning away, off, apart. According to Keplers first law of motion, all planets, comets. Hence, a body has a closest and a farthest point from its parent object, that is, a perihelion. Each extreme is known as an apsis, orbital eccentricity measures the flatness of the orbit. Because of the distance at aphelion, only 93. 55% of the solar radiation from the Sun falls on a given area of land as does at perihelion. However, this fluctuation does not account for the seasons, as it is summer in the northern hemisphere when it is winter in the southern hemisphere and vice versa. Instead, seasons result from the tilt of Earths axis, which is 23.4 degrees away from perpendicular to the plane of Earths orbit around the sun. Winter falls on the hemisphere where sunlight strikes least directly, and summer falls where sunlight strikes most directly, in the northern hemisphere, summer occurs at the same time as aphelion. Despite this, there are larger land masses in the northern hemisphere, consequently, summers are 2.3 °C warmer in the northern hemisphere than in the southern hemisphere under similar conditions. Apsis Ellipse Solstice Dates and times of Earths perihelion and aphelion, 2000–2025 from the United States Naval Observatory
7.
Astronomical unit
–
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
8.
Orders of magnitude (length)
–
The following are examples of orders of magnitude for different lengths. To help compare different orders of magnitude, the following list describes various lengths between 1. 6×10−35 meters and 101010122 meters,100 pm –1 Ångström 120 pm – radius of a gold atom 150 pm – Length of a typical covalent bond. 280 pm – Average size of the water molecule 298 pm – radius of a caesium atom, light travels 1 metre in 1⁄299,792,458, or 3. 3356409519815E-9 of a second. 25 metres – wavelength of the broadcast radio shortwave band at 12 MHz 29 metres – height of the lighthouse at Savudrija, Slovenia. 31 metres – wavelength of the broadcast radio shortwave band at 9.7 MHz 34 metres – height of the Split Point Lighthouse in Aireys Inlet, Victoria, Australia. 1 kilometre is equal to,1,000 metres 0.621371 miles 1,093.61 yards 3,280.84 feet 39,370.1 inches 100,000 centimetres 1,000,000 millimetres Side of a square of area 1 km2. Radius of a circle of area π km2,1.637 km – deepest dive of Lake Baikal in Russia, the worlds largest fresh water lake. 2.228 km – height of Mount Kosciuszko, highest point in Australia Most of Manhattan is from 3 to 4 km wide, farsang, a modern unit of measure commonly used in Iran and Turkey. Usage of farsang before 1926 may be for a precise unit derived from parasang. It is the altitude at which the FAI defines spaceflight to begin, to help compare orders of magnitude, this page lists lengths between 100 and 1,000 kilometres. 7.9 Gm – Diameter of Gamma Orionis 9, the newly improved measurement was 30% lower than the previous 2007 estimate. The size was revised in 2012 through improved measurement techniques and its faintness gives us an idea how our Sun would appear when viewed from even so close a distance as this. 350 Pm –37 light years – Distance to Arcturus 373.1 Pm –39.44 light years - Distance to TRAPPIST-1, a star recently discovered to have 7 planets around it. 400 Pm –42 light years – Distance to Capella 620 Pm –65 light years – Distance to Aldebaran This list includes distances between 1 and 10 exametres. 13 Em –1,300 light years – Distance to the Orion Nebula 14 Em –1,500 light years – Approximate thickness of the plane of the Milky Way galaxy at the Suns location 30.8568 Em –3,261. At this scale, expansion of the universe becomes significant, Distance of these objects are derived from their measured redshifts, which depends on the cosmological models used. At this scale, expansion of the universe becomes significant, Distance of these objects are derived from their measured redshifts, which depends on the cosmological models used. 590 Ym –62 billion light years – Cosmological event horizon, displays orders of magnitude in successively larger rooms Powers of Ten Travel across the Universe
9.
Semi-major and semi-minor axes
–
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
10.
Orbital eccentricity
–
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
11.
Mean anomaly
–
In celestial mechanics, the mean anomaly is an angle used in calculating the position of a body in an elliptical orbit in the classical two-body problem. Define T as the time required for a body to complete one orbit. In time T, the radius vector sweeps out 2π radians or 360°. The average rate of sweep, n, is then n =2 π T or n =360 ∘ T, define τ as the time at which the body is at the pericenter. From the above definitions, a new quantity, M, the mean anomaly can be defined M = n, because the rate of increase, n, is a constant average, the mean anomaly increases uniformly from 0 to 2π radians or 0° to 360° during each orbit. It is equal to 0 when the body is at the pericenter, π radians at the apocenter, if the mean anomaly is known at any given instant, it can be calculated at any later instant by simply adding n δt where δt represents the time difference. Mean anomaly does not measure an angle between any physical objects and it is simply a convenient uniform measure of how far around its orbit a body has progressed since pericenter. The mean anomaly is one of three parameters that define a position along an orbit, the other two being the eccentric anomaly and the true anomaly. Define l as the longitude, the angular distance of the body from the same reference direction. Thus mean anomaly is also M = l − ϖ, mean angular motion can also be expressed, n = μ a 3, where μ is a gravitational parameter which varies with the masses of the objects, and a is the semi-major axis of the orbit. Mean anomaly can then be expanded, M = μ a 3, and here mean anomaly represents uniform angular motion on a circle of radius a
12.
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
13.
Orbital inclination
–
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
14.
Longitude of the ascending node
–
The longitude of the ascending node is one of the orbital elements used to specify the orbit of an object in space. It is the angle from a direction, called the origin of longitude, to the direction of the ascending node. The ascending node is the point where the orbit of the passes through the plane of reference. Commonly used reference planes and origins of longitude include, For a geocentric orbit, Earths equatorial plane as the plane. In this case, the longitude is called the right ascension of the ascending node. The angle is measured eastwards from the First Point of Aries to the node, for a heliocentric orbit, the ecliptic as the reference plane, and the First Point of Aries as the origin of longitude. The angle is measured counterclockwise from the First Point of Aries to the node, the angle is measured eastwards from north to the node. pp.40,72,137, chap. In the case of a star known only from visual observations, it is not possible to tell which node is ascending. In this case the orbital parameter which is recorded is the longitude of the node, Ω, here, n=<nx, ny, nz> is a vector pointing towards the ascending node. The reference plane is assumed to be the xy-plane, and the origin of longitude is taken to be the positive x-axis, K is the unit vector, which is the normal vector to the xy reference plane. For non-inclined orbits, Ω is undefined, for computation it is then, by convention, set equal to zero, that is, the ascending node is placed in the reference direction, which is equivalent to letting n point towards the positive x-axis. Kepler orbits Equinox Orbital node perturbation of the plane can cause revolution of the ascending node
15.
Argument of periapsis
–
The argument of periapsis, symbolized as ω, is one of the orbital elements of an orbiting body. Parametrically, ω is the angle from the ascending node to its periapsis. For specific types of orbits, words such as perihelion, perigee, periastron, an argument of periapsis of 0° means that the orbiting body will be at its closest approach to the central body at the same moment that it crosses the plane of reference from South to North. An argument of periapsis of 90° means that the body will reach periapsis at its northmost distance from the plane of reference. Adding the argument of periapsis to the longitude of the ascending node gives the longitude of the periapsis, however, especially in discussions of binary stars and exoplanets, the terms longitude of periapsis or longitude of periastron are often used synonymously with argument of periapsis. In the case of equatorial orbits, the argument is strictly undefined, where, ex and ey are the x- and y-components of the eccentricity vector e. In the case of circular orbits it is assumed that the periapsis is placed at the ascending node. Kepler orbit Orbital mechanics Orbital node
16.
Kilometre
–
The kilometre or kilometer is a unit of length in the metric system, equal to one thousand metres. K is occasionally used in some English-speaking countries as an alternative for the kilometre in colloquial writing. A slang term for the kilometre in the US military is klick, there are two common pronunciations for the word. It is generally preferred by the British Broadcasting Corporation and the Australian Broadcasting Corporation, many scientists and other users, particularly in countries where the metric system is not widely used, use the pronunciation with stress on the second syllable. The latter pronunciation follows the pattern used for the names of measuring instruments. The problem with this reasoning, however, is that the meter in those usages refers to a measuring device. The contrast is more obvious in countries using the British rather than American spelling of the word metre. When Australia introduced the system in 1975, the first pronunciation was declared official by the governments Metric Conversion Board. However, the Australian prime minister at the time, Gough Whitlam, by the 8 May 1790 decree, the Constituent assembly ordered the French Academy of Sciences to develop a new measurement system. In August 1793, the French National Convention decreed the metre as the length measurement system in the French Republic. The first name of the kilometre was Millaire, although the metre was formally defined in 1799, the myriametre was preferred to the kilometre for everyday use. The term myriamètre appeared a number of times in the text of Develeys book Physique dEmile, ou, Principes de la de la nature. French maps published in 1835 had scales showing myriametres and lieues de Poste, the Dutch, on the other hand, adopted the kilometre in 1817 but gave it the local name of the mijl. It was only in 1867 that the term became the only official unit of measure in the Netherlands to represent 1000 metres. In the US, the National Highway System Designation Act of 1995 prohibits the use of highway funds to convert existing signs or purchase new signs with metric units. Although the State DOTs had the option of using metric measurements or dual units, all of them abandoned metric measurements, the Manual on Uniform Traffic Control Devices since 2000 is published in both metric and American Customary Units. Some sporting disciplines feature 1000 m races in major events, but in other disciplines, even though records are catalogued
17.
Mass
–
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
18.
Density
–
The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ, although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume, ρ = m V, where ρ is the density, m is the mass, and V is the volume. In some cases, density is defined as its weight per unit volume. For a pure substance the density has the numerical value as its mass concentration. Different materials usually have different densities, and density may be relevant to buoyancy, purity, osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser. Thus a relative density less than one means that the floats in water. The density of a material varies with temperature and pressure and this variation is typically small for solids and liquids but much greater for gases. Increasing the pressure on an object decreases the volume of the object, increasing the temperature of a substance decreases its density by increasing its volume. In most materials, heating the bottom of a results in convection of the heat from the bottom to the top. This causes it to rise relative to more dense unheated material, the reciprocal of the density of a substance is occasionally called its specific volume, a term sometimes used in thermodynamics. Density is a property in that increasing the amount of a substance does not increase its density. Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated easily and compared with the mass, upon this discovery, he leapt from his bath and ran naked through the streets shouting, Eureka. As a result, the term eureka entered common parlance and is used today to indicate a moment of enlightenment, the story first appeared in written form in Vitruvius books of architecture, two centuries after it supposedly took place. Some scholars have doubted the accuracy of this tale, saying among other things that the method would have required precise measurements that would have been difficult to make at the time, from the equation for density, mass density has units of mass divided by volume. As there are units of mass and volume covering many different magnitudes there are a large number of units for mass density in use. The SI unit of kilogram per metre and the cgs unit of gram per cubic centimetre are probably the most commonly used units for density.1,000 kg/m3 equals 1 g/cm3. In industry, other larger or smaller units of mass and or volume are often more practical, see below for a list of some of the most common units of density
19.
Hour
–
An hour is a unit of time conventionally reckoned as 1⁄24 of a day and scientifically reckoned as 3, 599–3,601 seconds, depending on conditions. The seasonal, temporal, or unequal hour was established in the ancient Near East as 1⁄12 of the night or daytime, such hours varied by season, latitude, and weather. It was subsequently divided into 60 minutes, each of 60 seconds, the modern English word hour is a development of the Anglo-Norman houre and Middle English ure, first attested in the 13th century. It displaced the Old English tide and stound, the Anglo-Norman term was a borrowing of Old French ure, a variant of ore, which derived from Latin hōra and Greek hṓrā. Like Old English tīd and stund, hṓrā was originally a word for any span of time, including seasons. Its Proto-Indo-European root has been reconstructed as *yeh₁-, making hour distantly cognate with year, the time of day is typically expressed in English in terms of hours. Whole hours on a 12-hour clock are expressed using the contracted phrase oclock, Hours on a 24-hour clock are expressed as hundred or hundred hours. Fifteen and thirty minutes past the hour is expressed as a quarter past or after and half past, respectively, fifteen minutes before the hour may be expressed as a quarter to, of, till, or before the hour. Sumerian and Babylonian hours divided the day and night into 24 equal hours, the ancient Egyptians began dividing the night into wnwt at some time before the compilation of the Dynasty V Pyramid Texts in the 24th century BC. By 2150 BC, diagrams of stars inside Egyptian coffin lids—variously known as diagonal calendars or star clocks—attest that there were exactly 12 of these. The coffin diagrams show that the Egyptians took note of the risings of 36 stars or constellations. Each night, the rising of eleven of these decans were noted, the original decans used by the Egyptians would have fallen noticeably out of their proper places over a span of several centuries. By the time of Amenhotep III, the priests at Karnak were using water clocks to determine the hours and these were filled to the brim at sunset and the hour determined by comparing the water level against one of its twelve gauges, one for each month of the year. During the New Kingdom, another system of decans was used, the later division of the day into 12 hours was accomplished by sundials marked with ten equal divisions. The morning and evening periods when the failed to note time were observed as the first and last hours. The Egyptian hours were closely connected both with the priesthood of the gods and with their divine services, by the New Kingdom, each hour was conceived as a specific region of the sky or underworld through which Ras solar bark travelled. Protective deities were assigned to each and were used as the names of the hours, as the protectors and resurrectors of the sun, the goddesses of the night hours were considered to hold power over all lifespans and thus became part of Egyptian funerary rituals. The Egyptian for astronomer, used as a synonym for priest, was wnwty, the earliest forms of wnwt include one or three stars, with the later solar hours including the determinative hieroglyph for sun
20.
Day
–
In common usage, it is either an interval equal to 24 hours or daytime, the consecutive period of time during which the Sun is above the horizon. The period of time during which the Earth completes one rotation with respect to the Sun is called a solar day, several definitions of this universal human concept are used according to context, need and convenience. In 1960, the second was redefined in terms of the motion of the Earth. The unit of measurement day, redefined in 1960 as 86400 SI seconds and symbolized d, is not an SI unit, but is accepted for use with SI. The word day may also refer to a day of the week or to a date, as in answer to the question. The life patterns of humans and many species are related to Earths solar day. In recent decades the average length of a day on Earth has been about 86400.002 seconds. A day, understood as the span of time it takes for the Earth to make one rotation with respect to the celestial background or a distant star, is called a stellar day. This period of rotation is about 4 minutes less than 24 hours, mainly due to tidal effects, the Earths rotational period is not constant, resulting in further minor variations for both solar days and stellar days. Other planets and moons have stellar and solar days of different lengths to Earths, besides the day of 24 hours, the word day is used for several different spans of time based on the rotation of the Earth around its axis. An important one is the day, defined as the time it takes for the Sun to return to its culmination point. Because the Earth orbits the Sun elliptically as the Earth spins on an inclined axis, on average over the year this day is equivalent to 24 hours. A day, in the sense of daytime that is distinguished from night-time, is defined as the period during which sunlight directly reaches the ground. The length of daytime averages slightly more than half of the 24-hour day, two effects make daytime on average longer than nights. The Sun is not a point, but has an apparent size of about 32 minutes of arc, additionally, the atmosphere refracts sunlight in such a way that some of it reaches the ground even when the Sun is below the horizon by about 34 minutes of arc. So the first light reaches the ground when the centre of the Sun is still below the horizon by about 50 minutes of arc, the difference in time depends on the angle at which the Sun rises and sets, but can amount to around seven minutes. Ancient custom has a new day start at either the rising or setting of the Sun on the local horizon, the exact moment of, and the interval between, two sunrises or sunsets depends on the geographical position, and the time of year. A more constant day can be defined by the Sun passing through the local meridian, the exact moment is dependent on the geographical longitude, and to a lesser extent on the time of the year
21.
Asteroid
–
Asteroids are minor planets, especially those of the inner Solar System. The larger ones have also been called planetoids and these terms have historically been applied to any astronomical object orbiting the Sun that did not show the disc of a planet and was not observed to have the characteristics of an active comet. As minor planets in the outer Solar System were discovered and found to have volatile-based surfaces that resemble those of comets, in this article, the term asteroid refers to the minor planets of the inner Solar System including those co-orbital with Jupiter. There are millions of asteroids, many thought to be the remnants of planetesimals. The large majority of known asteroids orbit in the belt between the orbits of Mars and Jupiter, or are co-orbital with Jupiter. However, other orbital families exist with significant populations, including the near-Earth objects, individual asteroids are classified by their characteristic spectra, with the majority falling into three main groups, C-type, M-type, and S-type. These were named after and are identified with carbon-rich, metallic. The size of asteroids varies greatly, some reaching as much as 1000 km across, asteroids are differentiated from comets and meteoroids. In the case of comets, the difference is one of composition, while asteroids are composed of mineral and rock, comets are composed of dust. In addition, asteroids formed closer to the sun, preventing the development of the aforementioned cometary ice, the difference between asteroids and meteoroids is mainly one of size, meteoroids have a diameter of less than one meter, whereas asteroids have a diameter of greater than one meter. Finally, meteoroids can be composed of either cometary or asteroidal materials, only one asteroid,4 Vesta, which has a relatively reflective surface, is normally visible to the naked eye, and this only in very dark skies when it is favorably positioned. Rarely, small asteroids passing close to Earth may be visible to the eye for a short time. As of March 2016, the Minor Planet Center had data on more than 1.3 million objects in the inner and outer Solar System, the United Nations declared June 30 as International Asteroid Day to educate the public about asteroids. The date of International Asteroid Day commemorates the anniversary of the Tunguska asteroid impact over Siberia, the first asteroid to be discovered, Ceres, was found in 1801 by Giuseppe Piazzi, and was originally considered to be a new planet. In the early half of the nineteenth century, the terms asteroid. Asteroid discovery methods have improved over the past two centuries. This task required that hand-drawn sky charts be prepared for all stars in the band down to an agreed-upon limit of faintness. On subsequent nights, the sky would be charted again and any moving object would, hopefully, the expected motion of the missing planet was about 30 seconds of arc per hour, readily discernible by observers
22.
Asteroid belt
–
The asteroid belt is the circumstellar disc in the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets, the asteroid belt is also termed the main asteroid belt or main belt to distinguish it from other asteroid populations in the Solar System such as near-Earth asteroids and trojan asteroids. About half the mass of the belt is contained in the four largest asteroids, Ceres, Vesta, Pallas, the total mass of the asteroid belt is approximately 4% that of the Moon, or 22% that of Pluto, and roughly twice that of Plutos moon Charon. Ceres, the belts only dwarf planet, is about 950 km in diameter, whereas Vesta, Pallas. The remaining bodies range down to the size of a dust particle, the asteroid material is so thinly distributed that numerous unmanned spacecraft have traversed it without incident. Nonetheless, collisions between large asteroids do occur, and these can form a family whose members have similar orbital characteristics. Individual asteroids within the belt are categorized by their spectra. The asteroid belt formed from the solar nebula as a group of planetesimals. Planetesimals are the precursors of the protoplanets. Between Mars and Jupiter, however, gravitational perturbations from Jupiter imbued the protoplanets with too much energy for them to accrete into a planet. Collisions became too violent, and instead of fusing together, the planetesimals, as a result,99. 9% of the asteroid belts original mass was lost in the first 100 million years of the Solar Systems history. Some fragments eventually found their way into the inner Solar System, Asteroid orbits continue to be appreciably perturbed whenever their period of revolution about the Sun forms an orbital resonance with Jupiter. At these orbital distances, a Kirkwood gap occurs as they are swept into other orbits. Classes of small Solar System bodies in other regions are the objects, the centaurs, the Kuiper belt objects, the scattered disc objects, the sednoids. On 22 January 2014, ESA scientists reported the detection, for the first definitive time, of water vapor on Ceres, the detection was made by using the far-infrared abilities of the Herschel Space Observatory. The finding was unexpected because comets, not asteroids, are considered to sprout jets. According to one of the scientists, The lines are becoming more and more blurred between comets and asteroids. This pattern, now known as the Titius–Bode law, predicted the semi-major axes of the six planets of the provided one allowed for a gap between the orbits of Mars and Jupiter
23.
Mars-crosser asteroid
–
A Mars-crosser is an asteroid whose orbit crosses that of Mars. The known numbered Mars-crossers are listed here and they include the two numbered Mars trojans 5261 Eureka and 1998 VF31. Many databases, for instance the JPL Small-Body Database, only list asteroids with a greater than 1.3 AU as Mars-crossers. An asteroid with a less than this is classed as a near-Earth object even though it is crossing the orbit of Mars as well as crossing that of Earth. Nevertheless, these objects are listed on this page, a grazer is an object with a perihelion below the aphelion of Mars but above the Martian perihelion. The JPL SBDB lists 13,500 Mars-crossing asteroids, only 18 MCAs are brighter than absolute magnitude 12.5, which typically makes these asteroids with H<12.5 more than 13 km in diameter depending on the albedo. The smallest known MCAs have a magnitude of around 24 and are typically less than 100 meters in diameter. Instead, they are categorized as Near Earth Objects
24.
Proper orbital elements
–
The proper orbital elements of an orbit are constants of motion of an object in space that remain practically unchanged over an astronomically long timescale. The term is used to describe the three quantities, proper semimajor axis, proper eccentricity, and proper inclination. The proper elements can be contrasted with the osculating Keplerian orbital elements observed at a time or epoch, such as the semi-major axis, eccentricity. Those osculating elements change in a quasi-periodic and predictable due to such effects as perturbations from planets or other bodies. In the Solar System, such changes usually occur on timescales of thousands of years, for most bodies, the osculating elements are relatively close to the proper elements because precession and perturbation effects are relatively small. For over 99% of asteroids in the belt, the differences are less than 0.02 AU,0.1. Nevertheless, this difference is non-negligible for any purposes where precision is of importance, to obtain proper elements for an object, one usually conducts a detailed simulation of its motion over timespans of several millions of years. Such a simulation must take into account many details of celestial mechanics including perturbations by the planets, subsequently, one extracts quantities from the simulation which remain unchanged over this long timespan, for example, the mean inclination, eccentricity, and semi-major axis. These are the orbital elements. Historically, various approximate analytic calculations were made, starting with those of Kiyotsugu Hirayama in the early 20th century, later analytic methods often included thousands of perturbing corrections for each particular object. At present the most prominent use of orbital elements is in the study of asteroid families. A Mars-crosser asteroid 132 Aethra is the lowest numbered asteroid to not have any proper orbital elements, the Determination of Asteroid Proper Elements, p. 603-612 in Asteroids III, University of Arizona Press. Latest calculations of proper elements for numbered minor planets at astDys
25.
Perturbation (astronomy)
–
In astronomy, perturbation is the complex motion of a massive body subject to forces other than the gravitational attraction of a single other massive body. The other forces can include a body, resistance, as from an atmosphere. The study of perturbations began with the first attempts to predict planetary motions in the sky, in ancient times the causes were a mystery. Newton, at the time he formulated his laws of motion and of gravitation, applied them to the first analysis of perturbations, the complex motions of gravitational perturbations can be broken down. The hypothetical motion that the body follows under the effect of one other body only is typically a conic section. This is called a problem, or an unperturbed Keplerian orbit. The differences between that and the motion of the body are perturbations due to the additional gravitational effects of the remaining body or bodies. If there is one other significant body then the perturbed motion is a three-body problem. A general analytical solution exists for the problem, when more than two bodies are considered analytic solutions exist only for special cases. Even the two-body problem becomes insoluble if one of the bodies is irregular in shape, most systems that involve multiple gravitational attractions present one primary body which is dominant in its effects. The gravitational effects of the bodies can be treated as perturbations of the hypothetical unperturbed motion of the planet or satellite around its primary body. In methods of general perturbations, general differential equations, either of motion or of change in the elements, are solved analytically, usually by series expansions. The result is expressed in terms of algebraic and trigonometric functions of the orbital elements of the body in question. This can be applied generally to many different sets of conditions, historically, general perturbations were investigated first. The classical methods are known as variation of the elements, variation of parameters or variation of the constants of integration, in these methods, it is considered that the body is always moving in a conic section, however the conic section is constantly changing due to the perturbations. General perturbations is applicable if the perturbing forces are about one order of magnitude smaller, or less. In the Solar System, this is usually the case, Jupiter, general perturbation methods are preferred for some types of problems, as the source of certain observed motions are readily found. In effect, the positions and velocities are perturbed directly, special perturbations can be applied to any problem in celestial mechanics, as it is not limited to cases where the perturbing forces are small
26.
Orbit
–
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet about a star or a natural satellite around a planet. Normally, orbit refers to a regularly repeating path around a body, to a close approximation, planets and satellites follow elliptical orbits, with the central mass being orbited at a focal point of the ellipse, as described by Keplers laws of planetary motion. For ease of calculation, in most situations orbital motion is adequately approximated by Newtonian Mechanics, historically, the apparent motions of the planets were described by European and Arabic philosophers using the idea of celestial spheres. This model posited the existence of perfect moving spheres or rings to which the stars and it assumed the heavens were fixed apart from the motion of the spheres, and was developed without any understanding of gravity. After the planets motions were accurately measured, theoretical mechanisms such as deferent. Originally geocentric it was modified by Copernicus to place the sun at the centre to help simplify the model, the model was further challenged during the 16th century, as comets were observed traversing the spheres. The basis for the understanding of orbits was first formulated by Johannes Kepler whose results are summarised in his three laws of planetary motion. Second, he found that the speed of each planet is not constant, as had previously been thought. Third, Kepler found a relationship between the orbital properties of all the planets orbiting the Sun. For the planets, the cubes of their distances from the Sun are proportional to the squares of their orbital periods. Jupiter and Venus, for example, are respectively about 5.2 and 0.723 AU distant from the Sun, their orbital periods respectively about 11.86 and 0.615 years. The proportionality is seen by the fact that the ratio for Jupiter,5. 23/11.862, is equal to that for Venus,0. 7233/0.6152. Idealised orbits meeting these rules are known as Kepler orbits, isaac Newton demonstrated that Keplers laws were derivable from his theory of gravitation and that, in general, the orbits of bodies subject to gravity were conic sections. Newton showed that, for a pair of bodies, the sizes are in inverse proportion to their masses. Where one body is more massive than the other, it is a convenient approximation to take the center of mass as coinciding with the center of the more massive body. Lagrange developed a new approach to Newtonian mechanics emphasizing energy more than force, in a dramatic vindication of classical mechanics, in 1846 le Verrier was able to predict the position of Neptune based on unexplained perturbations in the orbit of Uranus. This led astronomers to recognize that Newtonian mechanics did not provide the highest accuracy in understanding orbits, in relativity theory, orbits follow geodesic trajectories which are usually approximated very well by the Newtonian predictions but the differences are measurable. Essentially all the evidence that can distinguish between the theories agrees with relativity theory to within experimental measurement accuracy
27.
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
28.
Planet
–
The term planet is ancient, with ties to history, astrology, science, mythology, and religion. Several planets in the Solar System can be seen with the naked eye and these were regarded by many early cultures as divine, or as emissaries of deities. As scientific knowledge advanced, human perception of the planets changed, in 2006, the International Astronomical Union officially adopted a resolution defining planets within the Solar System. This definition is controversial because it excludes many objects of mass based on where or what they orbit. The planets were thought by Ptolemy to orbit Earth in deferent, at about the same time, by careful analysis of pre-telescopic observation data collected by Tycho Brahe, Johannes Kepler found the planets orbits were not circular but elliptical. As observational tools improved, astronomers saw that, like Earth, the planets rotated around tilted axes, and some shared such features as ice caps and seasons. Since the dawn of the Space Age, close observation by space probes has found that Earth and the planets share characteristics such as volcanism, hurricanes, tectonics. Planets are generally divided into two types, large low-density giant planets, and smaller rocky terrestrials. Under IAU definitions, there are eight planets in the Solar System, in order of increasing distance from the Sun, they are the four terrestrials, Mercury, Venus, Earth, and Mars, then the four giant planets, Jupiter, Saturn, Uranus, and Neptune. Six of the planets are orbited by one or more natural satellites, several thousands of planets around other stars have been discovered in the Milky Way. e. in the habitable zone. On December 20,2011, the Kepler Space Telescope team reported the discovery of the first Earth-sized extrasolar planets, Kepler-20e and Kepler-20f, orbiting a Sun-like star, Kepler-20. A2012 study, analyzing gravitational microlensing data, estimates an average of at least 1.6 bound planets for every star in the Milky Way, around one in five Sun-like stars is thought to have an Earth-sized planet in its habitable zone. The idea of planets has evolved over its history, from the lights of antiquity to the earthly objects of the scientific age. The concept has expanded to include not only in the Solar System. The ambiguities inherent in defining planets have led to much scientific controversy, the five classical planets, being visible to the naked eye, have been known since ancient times and have had a significant impact on mythology, religious cosmology, and ancient astronomy. In ancient times, astronomers noted how certain lights moved across the sky, as opposed to the fixed stars, ancient Greeks called these lights πλάνητες ἀστέρες or simply πλανῆται, from which todays word planet was derived. In ancient Greece, China, Babylon, and indeed all pre-modern civilizations, it was almost universally believed that Earth was the center of the Universe and that all the planets circled Earth. The first civilization known to have a theory of the planets were the Babylonians
29.
Mars
–
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, after Mercury. Named after the Roman god of war, it is referred to as the Red Planet because the iron oxide prevalent on its surface gives it a reddish appearance. Mars is a planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys, deserts, and polar ice caps of Earth. The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, Mars is the site of Olympus Mons, the largest volcano and second-highest known mountain in the Solar System, and of Valles Marineris, one of the largest canyons in the Solar System. The smooth Borealis basin in the northern hemisphere covers 40% of the planet, Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids, similar to 5261 Eureka, a Mars trojan, there are ongoing investigations assessing the past habitability potential of Mars, as well as the possibility of extant life. Future astrobiology missions are planned, including the Mars 2020 and ExoMars rovers, liquid water cannot exist on the surface of Mars due to low atmospheric pressure, which is about 6⁄1000 that of the Earths, except at the lowest elevations for short periods. The two polar ice caps appear to be largely of water. The volume of ice in the south polar ice cap, if melted. On November 22,2016, NASA reported finding a large amount of ice in the Utopia Planitia region of Mars. The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior, Mars can easily be seen from Earth with the naked eye, as can its reddish coloring. Its apparent magnitude reaches −2.91, which is surpassed only by Jupiter, Venus, the Moon, optical ground-based telescopes are typically limited to resolving features about 300 kilometers across when Earth and Mars are closest because of Earths atmosphere. Mars is approximately half the diameter of Earth with an area only slightly less than the total area of Earths dry land. Mars is less dense than Earth, having about 15% of Earths volume and 11% of Earths mass, the red-orange appearance of the Martian surface is caused by iron oxide, or rust. It can look like butterscotch, other common colors include golden, brown, tan. Like Earth, Mars has differentiated into a metallic core overlaid by less dense materials. Current models of its interior imply a core with a radius of about 1,794 ±65 kilometers, consisting primarily of iron and this iron sulfide core is thought to be twice as rich in lighter elements than Earths. The core is surrounded by a mantle that formed many of the tectonic and volcanic features on the planet
30.
Lost minor planet
–
Lost minor planets are minor planets that observers lose track of due to too short an observation arc to accurately predict the future location of the minor planet. Many of the asteroids that were discovered early were lost and rediscovered in the 1980s and 1990s, some minor planets and comets discovered in previous decades were lost because the observational data obtained was insufficient to determine a reliable orbit. Without this information, astronomers would not know where to look for the object at future dates, occasionally, a newly discovered object turns out to be a rediscovery of a previously lost object. This can be determined by calculating the new objects orbit backwards and this may greatly extend the observation arc, thus fixing the orbit much more precisely. For lost comets the back orbit calculations are especially tricky because of forces that can affect their orbits. However, Brian G. Marsden has specialized in calculating such nongravitational forces, notably, he successfully predicted the 1992 return of the once-lost periodic comet Swift–Tuttle. This is a selection of some early lost or notable asteroids with their discovery and rediscovery dates. The true number of lost asteroids may be over 150,000, there are also about 30,000 unnumbered bodies with a condition code of U = 9, indicating the highest possible uncertainty of their orbit determination. Many of these bodies have been observed if not decades ago. There are also more than a thousand objects with an observation arc of one or two days only. There are earlier examples also, such as 132 Aethra, which was lost between 1873 and 1922, leif Kahl Kristensen at the University of Aarhus rediscovered 452 Hamiltonia and 1537 Transylvania, along with numerous other small objects, in 1981. He named it China, or 中華 Zhōnghuá, however, this asteroid was not observed beyond its initial appearance and a precise orbit could not be calculated. However, in 1986, the newly discovered object 1986 QK1 was confirmed to be a rediscovery of the original 1928 UF, and this object was named 3789 Zhongguo, the near-Earth asteroid 1950 DA was discovered on 23 February 1950 by Carl Wirtanen at Lick Observatory. It was observed for 17 days and then lost, since not enough observations were made to allow its orbit to be plotted and it was then rediscovered on 31 December 2000. The chance it will impact Earth on 16 March 2880 is about 1 in 4,000,7796 Járacimrman was discovered at the Czech Kleť Observatory on 16 January 1996 by Zdeněk Moravec and was designated 1996 BG. It was observed until April 1996 and then in June and July 1997, recently lost minor planets 2007 WD5 is a 50 m Apollo-class NEO and a Mars-crosser discovered on 20 November 2007, by Andrea Boattini of the Catalina Sky Survey. Early observations of 2007 WD5 caused excitement amongst the community when it was estimated as having as high as a 1 in 25 chance of colliding with Mars on 30 January 2008. However, by 9 January 2008 additional observations allowed NASAs Near Earth Object Program to reduce the uncertainty region resulting in only a 1-in-10,000 chance of impact,2007 WD5 most likely passed Mars at a distance of 6.5 Mars radii
31.
Theseus
–
Theseus was a founder-hero, like Perseus, Cadmus, or Heracles, all of whom battled and overcame foes that were identified with an archaic religious and social order. As Heracles was the Dorian hero, Theseus was a hero, considered by Athenians as their own great reformer, his name comes from the same root as θεσμός. The myths surrounding Theseus—his journeys, exploits, and family—have provided material for fiction throughout the ages, Theseus was responsible for the synoikismos —the political unification of Attica under Athens, represented emblematically in his journey of labours, subduing ogres and monstrous beasts. Because he was the king, Theseus built and occupied a palace on the fortress of the Acropolis that may have been similar to the palace that was excavated in Mycenae. Pausanias reports that after the synoikismos, Theseus established a cult of Aphrodite Pandemos, Plutarchs vita of Theseus makes use of varying accounts of the death of the Minotaur, Theseus escape, and the love of Ariadne for Theseus. Plutarchs sources, not all of whose texts have survived independently, included Pherecydes, Demon, Philochorus, Aegeus, one of the primordial kings of Athens, was childless. Desiring an heir, he asked the oracle at Delphi for advice and her cryptic words were Do not loosen the bulging mouth of the wineskin until you have reached the height of Athens, lest you die of grief. Aegeus did not understand the prophecy and was disappointed and he asked the advice of his host Pittheus, king of Troezen. Pittheus understood the prophecy, got Aegeus drunk, and gave Aegeus his daughter Aethra, but following the instructions of Athena in a dream, Aethra left the sleeping Aegeus and waded across to the island of Sphairia that lay close to Troezens shore. There she poured a libation to Sphairos and Poseidon, and was possessed by the sea god in the night. The mix gave Theseus a combination of divine as well as mortal characteristics in his nature, such double paternity, with one immortal, after Aethra became pregnant, Aegeus decided to return to Athens. In Athens, Aegeus was joined by Medea, who had left Corinth after slaughtering the children she had borne, priestess and consort together represented the old order in Athens. Thus Theseus was raised in his mothers land, when Theseus grew up and became a brave young man, he moved the rock and recovered his fathers tokens. His mother then told him the truth about his fathers identity, young, brave, and ambitious, Theseus decided to go alone by the land route and defeated a great many bandits along the way. At the Isthmian entrance to the Underworld was a robber named Sinis and he would capture travelers, tie them between two pine trees that were bent down to the ground, and then let the trees go, tearing his victims apart. Theseus killed him by his own method and he then became intimate with Siniss daughter, Perigune, fathering the child Melanippus. In another deed north of the Isthmus, at a place called Crommyon, he killed an enormous pig, some versions name the sow herself as Phaea. The Bibliotheca described the Crommyonian Sow as an offspring of Typhon, near Megara, an elderly robber named Sciron forced travellers along the narrow cliff-face pathway to wash his feet
32.
Greek mythology
–
It was a part of the religion in ancient Greece. Greek mythology is explicitly embodied in a collection of narratives. Greek myth attempts to explain the origins of the world, and details the lives and adventures of a variety of gods, goddesses, heroes, heroines. These accounts initially were disseminated in a tradition, today the Greek myths are known primarily from ancient Greek literature. The oldest known Greek literary sources, Homers epic poems Iliad and Odyssey, focus on the Trojan War, archaeological findings provide a principal source of detail about Greek mythology, with gods and heroes featured prominently in the decoration of many artifacts. Geometric designs on pottery of the eighth century BC depict scenes from the Trojan cycle as well as the adventures of Heracles, in the succeeding Archaic, Classical, and Hellenistic periods, Homeric and various other mythological scenes appear, supplementing the existing literary evidence. Greek mythology has had an influence on the culture, arts. Poets and artists from ancient times to the present have derived inspiration from Greek mythology and have discovered contemporary significance and relevance in the themes, Greek mythology is known today primarily from Greek literature and representations on visual media dating from the Geometric period from c. Mythical narration plays an important role in every genre of Greek literature. Nevertheless, the only general mythographical handbook to survive from Greek antiquity was the Library of Pseudo-Apollodorus and this work attempts to reconcile the contradictory tales of the poets and provides a grand summary of traditional Greek mythology and heroic legends. Apollodorus of Athens lived from c, 180–125 BC and wrote on many of these topics. His writings may have formed the basis for the collection, however the Library discusses events that occurred long after his death, among the earliest literary sources are Homers two epic poems, the Iliad and the Odyssey. Other poets completed the cycle, but these later and lesser poems now are lost almost entirely. Despite their traditional name, the Homeric Hymns have no connection with Homer. They are choral hymns from the part of the so-called Lyric age. Hesiods Works and Days, a poem about farming life, also includes the myths of Prometheus, Pandora. The poet gives advice on the best way to succeed in a dangerous world, lyrical poets often took their subjects from myth, but their treatment became gradually less narrative and more allusive. Greek lyric poets, including Pindar, Bacchylides and Simonides, and bucolic poets such as Theocritus and Bion, additionally, myth was central to classical Athenian drama
.png)
. Bibcode:2012P&SS...73...98C. doi:10.1016/j.pss.2012.03.009. Retrieved 2 November 2017. See Table 1.
_mathilde.jpg){kind=small}