1.
2060 Chiron
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2060 Chiron, also known as 95P/Chiron, is a minor planet in the outer Solar System, orbiting the Sun between Saturn and Uranus. Discovered in 1977 by Charles T. Kowal, it was the member of a new class of objects now known as centaurs—bodies orbiting between the asteroid belt and the Kuiper belt. Besides the four giant planets, Chiron and 10199 Chariklo, also a centaur, are the other bodies in the Solar System known to have rings. Although it was called an asteroid and classified only as a minor planet with the designation 2060 Chiron. Today it is classified as both a planet and a comet, and is accordingly also known by the cometary designation 95P/Chiron. Chiron is named after the centaur Chiron in Greek mythology, michael Brown lists it as possibly a dwarf planet with a measured diameter of 206 km which is near the lower limit for an icy dwarf planet. Chiron was discovered on 1 November 1977 by Charles Kowal from images taken on 18 October at Palomar Observatory and it was given the temporary designation of 1977 UB. It was found near aphelion and at the time of discovery it was the most distant known minor planet, Chiron was even claimed as the tenth planet by the press. Chiron was later found on several images, going back to 1895. It had been at perihelion in 1945 but was not discovered then because there were few searches being made at time. The Lowell Observatorys survey for distant planets would not have gone down faint enough in the 1930s and it was named Chiron in 1979 after Chiron, one of the centaurs, it was suggested that the names of other centaurs be reserved for objects of the same type. Chirons orbit was found to be eccentric, with perihelion just inside the orbit of Saturn. According to the program Solex, Chirons closest approach to Saturn in modern times was around May 720, during this passage Saturns gravity caused Chirons semi-major axis to decrease from 14. 55±0.12 AU to 13.7 AU. It does not come nearly as close to Uranus, Chiron crosses Uranuss orbit where the latter is farther than average from the Sun, Chiron attracted considerable interest because it was the first object discovered in such an orbit, well outside the asteroid belt. Chiron is classified as a centaur, the first of a class of objects orbiting between the outer planets, Chiron is a Saturn–Uranus object because its perihelion lies in Saturns zone of control and its aphelion lies in that of Uranus. Chiron is probably a refugee from the Kuiper belt and will become a short-period comet in about a million years. Chiron came to perihelion in 1996, the visible and near-infrared spectrum of Chiron is neutral, and is similar to that of C-type asteroids and the nucleus of Halleys Comet. The near-infrared spectrum of Chiron shows absence of water ice, the assumed size of an object depends on its absolute magnitude and the albedo
2.
New Horizons
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New Horizons is an interplanetary space probe that was launched as a part of NASAs New Frontiers program. Engineered by the Johns Hopkins University Applied Physics Laboratory and the Southwest Research Institute, on January 19,2006, New Horizons was launched from Cape Canaveral Air Force Station directly into an Earth-and-solar escape trajectory with a speed of about 16.26 kilometers per second. After a brief encounter with asteroid 132524 APL, New Horizons proceeded to Jupiter, making its closest approach on February 28,2007, most of the post-Jupiter voyage was spent in hibernation mode to preserve on-board systems, except for brief annual checkouts. On December 6,2014, New Horizons was brought online for the Pluto encounter. On January 15,2015, the New Horizons spacecraft began its approach phase to Pluto, on July 14,2015, at 11,49 UTC, it flew 12,500 km above the surface of Pluto, making it the first spacecraft to explore the dwarf planet. On October 25,2016, at 21,48 UTC, the last of the recorded data from the Pluto flyby was received from New Horizons. Having completed its flyby of Pluto, New Horizons has maneuvered for a flyby of Kuiper belt object 2014 MU69, expected to place on January 1,2019. Appointed as the principal investigator, Stern was described by Krimigis as the personification of the Pluto mission. New Horizons was based largely on Sterns work since Pluto 350, the New Horizons proposal was one of five that were officially submitted to NASA. It was later selected as one of two finalists to be subject to a concept study, in June 2001. In November 2001, New Horizons was officially selected for funding as part of the New Frontiers program. However, the new NASA Administrator appointed by the Bush Administration, Sean OKeefe, was not supportive of New Horizons, after an intense campaign to gain support for New Horizons, the Planetary Science Decadal Survey of 2003-2013 was published in the summer of 2002. New Horizons topped the list of projects considered the highest priority among the community in the medium-size category, ahead of missions to the Moon. Weiler stated that it was a result that administration was not going to fight, Alice Bowman became Mission Operations Manager. New Horizons is the first mission in NASAs New Frontiers mission category, larger and more expensive than the Discovery missions, the cost of the mission is approximately $700 million over 15 years. The spacecraft was built primarily by Southwest Research Institute and the Johns Hopkins Applied Physics Laboratory, the missions principal investigator is Alan Stern of the Southwest Research Institute. After separation from the vehicle, overall control was taken by Mission Operations Center at the Applied Physics Laboratory in Howard County. The science instruments are operated at Clyde Tombaugh Science Operations Center in Boulder, New Horizons was originally planned as a voyage to the only unexplored planet in the Solar System
3.
James W. Christy
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James Walter Jim Christy is an American astronomer. Christy was born in 1938 in Milwaukee, Wisconsin and he attended the University of Arizona and earned a Bachelor of Science degree in astronomy from there in 1965. On June 22,1978 while working at the United States Naval Observatory, he discovered that Pluto had a moon, the name remained unofficial until its adoption by the IAU in 1986. The discovery was made by examining an enlargement of a photographic plate of Pluto. This plate and others had been marked poor because the image of Pluto was thought to be a defect resulting from improper alignment. The 1965 plates included a note Pluto image elongated, but observatory astronomers, including Christy, however, Christy noticed that only Pluto was elongated—the background stars were not. Christys earlier work at the Naval Observatory had included photographing double stars, after examining images from observatory archives dating back to 1965, he concluded that the bulge was indeed a moon. The photographic evidence was considered convincing but not conclusive, however, based on Charons calculated orbit, a series of mutual eclipses of Pluto and Charon was predicted and observed, confirming the discovery. In late 2008, the asteroid 129564 Christy was named in his honor. † As of 2015, he resides in Flagstaff and he has been married to Charlene Mary since 1975 and has four children. Plutos Companion from the website Pluto, The Discovery of Planet X, by Brad Mager 25th Anniversary of the Discovery of Plutos moon CHARON from NASA JPL website
4.
Charon (mythology)
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A coin to pay Charon for passage, usually an obolus or danake, was sometimes placed in or on the mouth of a dead person. Some authors say that those who could not pay the fee, Charon is the son of Nyx and Erebus. Nyx and Erebus were brother and sister and he was also the brother of Thanatos and Hypnos. The word may be a euphemism for death, flashing eyes may indicate the anger or irascibility of Charon as he is often characterized in literature, but the etymology is not certain. The ancient historian Diodorus Siculus thought that the ferryman and his name had been imported from Egypt, Charon is depicted frequently in the art of ancient Greece. Attic funerary vases of the 5th and 4th centuries BC are often decorated with scenes of the dead boarding Charon’s boat. On the earlier such vases, he looks like a rough, unkempt Athenian seaman dressed in reddish-brown, holding his ferrymans pole in his right hand, hermes sometimes stands by in his role as psychopomp. On later vases, Charon is given a more “kindly and refined” demeanor, when the boatman tells Hercules to halt, the Greek hero uses his strength to gain passage, overpowering Charon with the boatmans own pole. In the second century, Lucian employed Charon as a figure in his Dialogues of the Dead, in the 14th century, Dante Alighieri described Charon in his Divine Comedy, drawing from Virgils depiction in Aeneid 6. Charon is the first named mythological character Dante meets in the underworld, Dante depicts him as having eyes of fire. In modern times, he is depicted as a living skeleton in a cowl. The French artist, Gustave Dore, depicted Charon in two of his illustrations for Dantes Divine Comedy, the Flemish painter, Joachim Patinir, depicted Charon in his Crossing the River Styx. And the Spanish painter, Jose Benlliure y Gil, portrayed Charon in his La Barca de Caronte, most accounts, including Pausanias and later Dantes Inferno, associate Charon with the swamps of the river Acheron. Ancient Greek literary sources – such as Pindar, Aeschylus, Euripides, Plato, roman poets, including Propertius, Ovid, and Statius, name the river as the Styx, perhaps following the geography of Virgil’s underworld in the Aeneid, where Charon is associated with both rivers. Charon, the dwarf planet of the Pluto-Charon system, is named after him. Haros is the modern Greek equivalent of Charon, and usage includes the curse you will be eaten by Haros, during the Korean War, the Greek Expeditionary Force defended an outpost called Outpost Harry. The Greek soldiers referred to it as Outpost Haros, Charon Media related to Charon at Wikimedia Commons The Theoi Project, KHARON Images of Charon in the Warburg Institute Iconographic Database
5.
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
6.
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
7.
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
8.
Ecliptic
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The ecliptic is the apparent path of the Sun on the celestial sphere, and is the basis for the ecliptic coordinate system. It also refers to the plane of this path, which is coplanar with the orbit of Earth around the Sun, the motions as described above are simplifications. Due to the movement of Earth around the Earth–Moon center of mass, due to further perturbations by the other planets of the Solar System, the Earth–Moon barycenter wobbles slightly around a mean position in a complex fashion. The ecliptic is actually the apparent path of the Sun throughout the course of a year, because Earth takes one year to orbit the Sun, the apparent position of the Sun also takes the same length of time to make a complete circuit of the ecliptic. With slightly more than 365 days in one year, the Sun moves a little less than 1° eastward every day, again, this is a simplification, based on a hypothetical Earth that orbits at uniform speed around the Sun. The actual speed with which Earth orbits the Sun varies slightly during the year, for example, the Sun is north of the celestial equator for about 185 days of each year, and south of it for about 180 days. The variation of orbital speed accounts for part of the equation of time, if the equator is projected outward to the celestial sphere, forming the celestial equator, it crosses the ecliptic at two points known as the equinoxes. The Sun, in its apparent motion along the ecliptic, crosses the equator at these points, one from south to north. The crossing from south to north is known as the equinox, also known as the first point of Aries. The crossing from north to south is the equinox or descending node. Likewise, the ecliptic itself is not fixed, the gravitational perturbations of the other bodies of the Solar System cause a much smaller motion of the plane of Earths orbit, and hence of the ecliptic, known as planetary precession. The combined action of two motions is called general precession, and changes the position of the equinoxes by about 50 arc seconds per year. Once again, this is a simplification, periodic motions of the Moon and apparent periodic motions of the Sun cause short-term small-amplitude periodic oscillations of Earths axis, and hence the celestial equator, known as nutation. Obliquity of the ecliptic is the used by astronomers for the inclination of Earths equator with respect to the ecliptic. It is about 23. 4° and is currently decreasing 0.013 degrees per hundred years due to planetary perturbations, the angular value of the obliquity is found by observation of the motions of Earth and other planets over many years. From 1984, the Jet Propulsion Laboratorys DE series of computer-generated ephemerides took over as the ephemeris of the Astronomical Almanac. Obliquity based on DE200, which analyzed observations from 1911 to 1979, was calculated, jPLs fundamental ephemerides have been continually updated. J. Laskar computed an expression to order T10 good to 0″. 04/1000 years over 10,000 years, all of these expressions are for the mean obliquity, that is, without the nutation of the equator included
9.
Longitude of the ascending node
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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
10.
March equinox
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In the Northern Hemisphere the March equinox is known as the vernal equinox, and in the Southern Hemisphere as the autumnal equinox. On the Gregorian calendar the Northward equinox can occur as early as 19 March or as late as 21 March. For a common year the computed time slippage is about 5 hours 49 minutes later than the previous year, and for a leap year about 18 hours 11 minutes earlier than the previous year. Balancing the increases of the years against the losses of the leap years keeps the calendar date of the March equinox from drifting more than one day from 20 March each year. The March equinox may be taken to mark the beginning of spring and the end of winter in the Northern Hemisphere but marks the beginning of autumn, in astronomy, the March equinox is the zero point of sidereal time and, consequently, right ascension. It also serves as a reference for calendars and celebrations in many human cultures, the March equinox is one point in time commonly used to determine the length of the tropical year. The mean tropical year is the average of all the tropical years measured from every point along the Earths orbit. The following table shows the small variations in timing over a period of time. The point where the Sun crosses the equator northwards is called the First Point of Aries. However, due to the precession of the equinoxes, this point is no longer in the constellation Aries, by the year 2600 it will be in Aquarius. The Earths axis causes the First Point of Aries to travel westwards across the sky at a rate of one degree every 72 years. It passed by a corner of Cetus at 0°10′ distance in the year 1489. In its apparent motion on the day of an equinox, the Suns disk crosses the Earths horizon directly to the east at dawn—rising, the March equinox, like all equinoxes, is characterized by having an almost exactly equal amount of daylight and night across most latitudes on Earth. Due to refraction of light rays in the Earths atmosphere the Sun will be visible above the horizon even when its disc is completely below the limb of the Earth and these conditions produce differentials of actual durations of light and darkness at various locations on Earth during an equinox. This is most notable at the extreme latitudes, where the Sun may be seen to travel sideways considerably during the dawn. The Persian calendar begins each year at the equinox, observationally determined at Tehran. The Indian national calendar starts the year on the day next to the equinox on 22 March with a 30-day month. The Julian calendar reform lengthened seven months and replaced the intercalary month with a day to be added every four years to February
11.
Natural satellite
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A natural satellite or moon is, in the most common usage, an astronomical body that orbits a planet or minor planet. In the Solar System there are six planetary satellite systems containing 178 known natural satellites, four IAU-listed dwarf planets are also known to have natural satellites, Pluto, Haumea, Makemake, and Eris. As of January 2012, over 200 minor-planet moons have been discovered, the Earth–Moon system is unique in that the ratio of the mass of the Moon to the mass of Earth is much greater than that of any other natural-satellite–planet ratio in the Solar System. At 3,474 km across, Earths Moon is 0.27 times the diameter of Earth, the first known natural satellite was the Moon, but it was considered a planet until Copernicus introduction of heliocentrism in 1543. Until the discovery of the Galilean satellites in 1610, however, galileo chose to refer to his discoveries as Planetæ, but later discoverers chose other terms to distinguish them from the objects they orbited. The first to use of the satellite to describe orbiting bodies was the German astronomer Johannes Kepler in his pamphlet Narratio de Observatis a se quatuor Iouis satellitibus erronibus in 1610. He derived the term from the Latin word satelles, meaning guard, attendant, or companion, the term satellite thus became the normal one for referring to an object orbiting a planet, as it avoided the ambiguity of moon. In 1957, however, the launching of the artificial object Sputnik created a need for new terminology, to further avoid ambiguity, the convention is to capitalize the word Moon when referring to Earths natural satellite, but not when referring to other natural satellites. A few recent authors define moon as a satellite of a planet or minor planet, there is no established lower limit on what is considered a moon. Small asteroid moons, such as Dactyl, have also been called moonlets, the upper limit is also vague. Two orbiting bodies are described as a double body rather than primary. Asteroids such as 90 Antiope are considered double asteroids, but they have not forced a clear definition of what constitutes a moon, some authors consider the Pluto–Charon system to be a double planet. In contrast, irregular satellites are thought to be captured asteroids possibly further fragmented by collisions, most of the major natural satellites of the Solar System have regular orbits, while most of the small natural satellites have irregular orbits. The Moon and possibly Charon are exceptions among large bodies in that they are thought to have originated by the collision of two large proto-planetary objects. The material that would have placed in orbit around the central body is predicted to have reaccreted to form one or more orbiting natural satellites. As opposed to planetary-sized bodies, asteroid moons are thought to form by this process. Triton is another exception, although large and in a close, circular orbit, its motion is retrograde, most regular moons in the Solar System are tidally locked to their respective primaries, meaning that the same side of the natural satellite always faces its planet. The only known exception is Saturns natural satellite Hyperion, which rotates chaotically because of the influence of Titan
12.
Pluto
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Pluto is a dwarf planet in the Kuiper belt, a ring of bodies beyond Neptune. It was the first Kuiper belt object to be discovered, Pluto was discovered by Clyde Tombaugh in 1930 and was originally considered to be the ninth planet from the Sun. After 1992, its planethood was questioned following the discovery of objects of similar size in the Kuiper belt. In 2005, Eris, which is 27% more massive than Pluto, was discovered and this led the International Astronomical Union to define the term planet formally in 2006, during their 26th General Assembly. That definition excluded Pluto and reclassified it as a dwarf planet, Pluto is the largest and second-most-massive known dwarf planet in the Solar System and the ninth-largest and tenth-most-massive known object directly orbiting the Sun. It is the largest known trans-Neptunian object by volume but is less massive than Eris, like other Kuiper belt objects, Pluto is primarily made of ice and rock and is relatively small—about one-sixth the mass of the Moon and one-third its volume. It has an eccentric and inclined orbit during which it ranges from 30 to 49 astronomical units or AU from the Sun. This means that Pluto periodically comes closer to the Sun than Neptune, light from the Sun takes about 5.5 hours to reach Pluto at its average distance. Pluto has five moons, Charon, Styx, Nix, Kerberos. Pluto and Charon are sometimes considered a system because the barycenter of their orbits does not lie within either body. The IAU has not formalized a definition for binary dwarf planets, on July 14,2015, the New Horizons spacecraft became the first spacecraft to fly by Pluto. During its brief flyby, New Horizons made detailed measurements and observations of Pluto, on October 25,2016, at 05,48 pm ET, the last bit of data was received from New Horizons from its close encounter with Pluto on July 14,2015. In the 1840s, Urbain Le Verrier used Newtonian mechanics to predict the position of the then-undiscovered planet Neptune after analysing perturbations in the orbit of Uranus. Subsequent observations of Neptune in the late 19th century led astronomers to speculate that Uranuss orbit was being disturbed by another planet besides Neptune, by 1909, Lowell and William H. Pickering had suggested several possible celestial coordinates for such a planet. Lowell and his observatory conducted his search until his death in 1916, unknown to Lowell, his surveys had captured two faint images of Pluto on March 19 and April 7,1915, but they were not recognized for what they were. There are fourteen other known prediscovery observations, with the oldest made by the Yerkes Observatory on August 20,1909. Percivals widow, Constance Lowell, entered into a legal battle with the Lowell Observatory over her late husbands legacy. Tombaughs task was to image the night sky in pairs of photographs, then examine each pair
13.
Flattening
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Flattening is a measure of the compression of a circle or sphere along a diameter to form an ellipse or an ellipsoid of revolution respectively. Other terms used are ellipticity, or oblateness, the usual notation for flattening is f and its definition in terms of the semi-axes of the resulting ellipse or ellipsoid is f l a t t e n i n g = f = a − b a. The compression factor is b/a in each case, for the ellipse, this factor is also the aspect ratio of the ellipse. There are two variants of flattening and when it is necessary to avoid confusion the above flattening is called the first flattening. The following definitions may be found in texts and online web texts In the following. All flattenings are zero for a circle, the flattenings are related to other parameters of the ellipse. For example, b = a = a, e 2 =2 f − f 2 =4 n 2, other values in the Solar System are Jupiter, f=1/16, Saturn, f= 1/10, the Moon f= 1/900. The flattening of the Sun is about 9×10−6, in 1687 Isaac Newton published the Principia in which he included a proof that a rotating self-gravitating fluid body in equilibrium takes the form of an oblate ellipsoid of revolution. The amount of flattening depends on the density and the balance of gravitational force, astronomy Earth ellipsoid Earths rotation Eccentricity Equatorial bulge Gravitational field Gravity formula Ovality Planetology Sphericity Roundness
14.
Spheroid
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A spheroid, or ellipsoid of revolution, is a quadric surface obtained by rotating an ellipse about one of its principal axes, in other words, an ellipsoid with two equal semi-diameters. If the ellipse is rotated about its axis, the result is a prolate spheroid. If the ellipse is rotated about its axis, the result is an oblate spheroid. If the generating ellipse is a circle, the result is a sphere, because of the combined effects of gravity and rotation, the Earths shape is not quite a sphere but instead is slightly flattened in the direction of its axis of rotation. For that reason, in cartography the Earth is often approximated by an oblate spheroid instead of a sphere, the current World Geodetic System model uses a spheroid whose radius is 6,378.137 km at the equator and 6,356.752 km at the poles. The semi-major axis a is the radius of the spheroid. There are two cases, c < a, oblate spheroid c > a, prolate spheroid The case of a = c reduces to a sphere. An oblate spheroid with c < a has surface area S o b l a t e =2 π a 2 where e 2 =1 − c 2 a 2. The oblate spheroid is generated by rotation about the z-axis of an ellipse with semi-major axis a and semi-minor axis c, therefore e may be identified as the eccentricity. A prolate spheroid with c > a has surface area S p r o l a t e =2 π a 2 where e 2 =1 − a 2 c 2. The prolate spheroid is generated by rotation about the z-axis of an ellipse with semi-major axis c and semi-minor axis a and these formulas are identical in the sense that the formula for Soblate can be used to calculate the surface area of a prolate spheroid and vice versa. However, e then becomes imaginary and can no longer directly be identified with the eccentricity, both of these results may be cast into many other forms using standard mathematical identities and relations between parameters of the ellipse. The volume inside a spheroid is 4π/3a2c ≈4. 19a2c, if A = 2a is the equatorial diameter, and C = 2c is the polar diameter, the volume is π/6A2C ≈0. 523A2C. Both of these curvatures are always positive, so every point on a spheroid is elliptic. These are just two of different parameters used to define an ellipse and its solid body counterparts. The most common shapes for the density distribution of protons and neutrons in an atomic nucleus are spherical, prolate and oblate spheroidal, deformed nuclear shapes occur as a result of the competition between electromagnetic repulsion between protons, surface tension and quantum shell effects. An extreme example of a planet in science fiction is Mesklin, in Hal Clements novel Mission of Gravity. The prolate spheroid is the shape of the ball in several sports, several moons of the Solar system approximate prolate spheroids in shape, though they are actually triaxial ellipsoids
15.
Volume
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Volume is the quantity of three-dimensional space enclosed by a closed surface, for example, the space that a substance or shape occupies or contains. Volume is often quantified numerically using the SI derived unit, the cubic metre, three dimensional mathematical shapes are also assigned volumes. Volumes of some simple shapes, such as regular, straight-edged, Volumes of a complicated shape can be calculated by integral calculus if a formula exists for the shapes boundary. Where a variance in shape and volume occurs, such as those that exist between different human beings, these can be calculated using techniques such as the Body Volume Index. One-dimensional figures and two-dimensional shapes are assigned zero volume in the three-dimensional space, the volume of a solid can be determined by fluid displacement. Displacement of liquid can also be used to determine the volume of a gas, the combined volume of two substances is usually greater than the volume of one of the substances. However, sometimes one substance dissolves in the other and the volume is not additive. In differential geometry, volume is expressed by means of the volume form, in thermodynamics, volume is a fundamental parameter, and is a conjugate variable to pressure. Any unit of length gives a unit of volume, the volume of a cube whose sides have the given length. For example, a cubic centimetre is the volume of a cube whose sides are one centimetre in length, in the International System of Units, the standard unit of volume is the cubic metre. The metric system also includes the litre as a unit of volume, thus 1 litre =3 =1000 cubic centimetres =0.001 cubic metres, so 1 cubic metre =1000 litres. Small amounts of liquid are often measured in millilitres, where 1 millilitre =0.001 litres =1 cubic centimetre. Capacity is defined by the Oxford English Dictionary as the applied to the content of a vessel, and to liquids, grain, or the like. Capacity is not identical in meaning to volume, though closely related, Units of capacity are the SI litre and its derived units, and Imperial units such as gill, pint, gallon, and others. Units of volume are the cubes of units of length, in SI the units of volume and capacity are closely related, one litre is exactly 1 cubic decimetre, the capacity of a cube with a 10 cm side. In other systems the conversion is not trivial, the capacity of a fuel tank is rarely stated in cubic feet, for example. The density of an object is defined as the ratio of the mass to the volume, the inverse of density is specific volume which is defined as volume divided by mass. Specific volume is an important in thermodynamics where the volume of a working fluid is often an important parameter of a system being studied
16.
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
17.
Density
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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
18.
Escape velocity
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The escape velocity from Earth is about 11.186 km/s at the surface. More generally, escape velocity is the speed at which the sum of a kinetic energy. With escape velocity in a direction pointing away from the ground of a massive body, once escape velocity is achieved, no further impulse need be applied for it to continue in its escape. When given a speed V greater than the speed v e. In these equations atmospheric friction is not taken into account, escape velocity is only required to send a ballistic object on a trajectory that will allow the object to escape the gravity well of the mass M. The existence of escape velocity is a consequence of conservation of energy, by adding speed to the object it expands the possible places that can be reached until with enough energy they become infinite. For a given gravitational potential energy at a position, the escape velocity is the minimum speed an object without propulsion needs to be able to escape from the gravity. Escape velocity is actually a speed because it does not specify a direction, no matter what the direction of travel is, the simplest way of deriving the formula for escape velocity is to use conservation of energy. Imagine that a spaceship of mass m is at a distance r from the center of mass of the planet and its initial speed is equal to its escape velocity, v e. At its final state, it will be a distance away from the planet. The same result is obtained by a calculation, in which case the variable r represents the radial coordinate or reduced circumference of the Schwarzschild metric. All speeds and velocities measured with respect to the field, additionally, the escape velocity at a point in space is equal to the speed that an object would have if it started at rest from an infinite distance and was pulled by gravity to that point. In common usage, the point is on the surface of a planet or moon. On the surface of the Earth, the velocity is about 11.2 km/s. However, at 9,000 km altitude in space, it is less than 7.1 km/s. The escape velocity is independent of the mass of the escaping object and it does not matter if the mass is 1 kg or 1,000 kg, what differs is the amount of energy required. For an object of mass m the energy required to escape the Earths gravitational field is GMm / r, a related quantity is the specific orbital energy which is essentially the sum of the kinetic and potential energy divided by the mass. An object has reached escape velocity when the orbital energy is greater or equal to zero
19.
Tidal locking
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Tidal locking occurs when, over the course of an orbit, there is no net transfer of angular momentum between an astronomical body and its gravitational partner. This state can result from the gradient between two co-orbiting bodies, acting over a sufficiently long period of time. In the case where the orbital eccentricity is zero, tidal locking results in one hemisphere of the revolving object constantly facing its partner. For example, the side of the Moon always faces the Earth. A tidally locked body in synchronous rotation takes just as long to rotate around its own axis as it does to revolve around its partner, usually, only the satellite is tidally locked to the larger body. However, if both the difference between the two bodies and the distance between them are relatively small, each may be tidally locked to the other, this is the case for Pluto. This effect is employed to stabilize some artificial satellites, the possibility of lifeforms existing on tidally-locked planets has been debated. The change in rotation rate necessary to lock a body B to a larger body A is caused by the torque applied by As gravity on bulges it has induced on B by tidal forces. These distortions are known as tidal bulges, when B is not yet tidally locked, the bulges travel over its surface, with one of the two high tidal bulges traveling close to the point where body A is overhead. Smaller bodies also experience distortion, but this distortion is less regular, the material of B exerts resistance to this periodic reshaping caused by the tidal force. In effect, some time is required to reshape B to the equilibrium shape. Seen from a point in space, the points of maximum bulge extension are displaced from the axis oriented toward A. Because the bulges are now displaced from the A–B axis, As gravitational pull on the mass in them exerts a torque on B. The torque on the A-facing bulge acts to bring Bs rotation in line with its period, whereas the back bulge. However, the bulge on the A-facing side is closer to A than the bulge by a distance of approximately Bs diameter. The net resulting torque from both bulges, then, is always in the direction that acts to synchronize Bs rotation with its orbital period and this results in a raising of Bs orbit about A in tandem with its rotational slowdown. For the other case where B starts off rotating too slowly, the tidal locking effect is also experienced by the larger body A, but at a slower rate because Bs gravitational effect is weaker due to Bs smaller mass. For example, Earths rotation is gradually being slowed by the Moon, current estimations are that this has helped lengthen the Earth day from about 6 hours to the current 24 hours
20.
Albedo
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Albedo is a measure for reflectance or optical brightness. It is dimensionless and measured on a scale from zero to one, surface albedo is defined as the ratio of radiation reflected to the radiation incident on a surface. The proportion reflected is not only determined by properties of the surface itself and these factors vary with atmospheric composition, geographic location and time. While bi-hemispherical reflectance is calculated for an angle of incidence. The temporal resolution may range from seconds to daily, seasonal or annual averages, unless given for a specific wavelength, albedo refers to the entire spectrum of solar radiation. Due to measurement constraints, it is given for the spectrum in which most solar energy reaches the surface. This spectrum includes visible light, which explains why surfaces with a low albedo appear dark, albedo is an important concept in climatology, astronomy, and environmental management. The term albedo was introduced into optics by Johann Heinrich Lambert in his 1760 work Photometria, any albedo in visible light falls within a range of about 0.9 for fresh snow to about 0.04 for charcoal, one of the darkest substances. Deeply shadowed cavities can achieve an effective albedo approaching the zero of a black body, when seen from a distance, the ocean surface has a low albedo, as do most forests, whereas desert areas have some of the highest albedos among landforms. Most land areas are in a range of 0.1 to 0.4. The average albedo of Earth is about 0.3 and this is far higher than for the ocean primarily because of the contribution of clouds. Earths surface albedo is regularly estimated via Earth observation satellite sensors such as NASAs MODIS instruments on board the Terra, thereby, the BRDF allows to translate observations of reflectance into albedo. Earths average surface temperature due to its albedo and the effect is currently about 15 °C. If Earth were frozen entirely, the temperature of the planet would drop below −40 °C. If only the land masses became covered by glaciers, the mean temperature of the planet would drop to about 0 °C. In contrast, if the entire Earth was covered by water — a so-called aquaplanet — the average temperature on the planet would rise to almost 27 °C, hence, the actual albedo α can then be given as, α = α ¯ + D α ¯ ¯. Directional-hemispherical reflectance is sometimes referred to as black-sky albedo and bi-hemispherical reflectance as white-sky albedo and these terms are important because they allow the albedo to be calculated for any given illumination conditions from a knowledge of the intrinsic properties of the surface. The albedos of planets, satellites and asteroids can be used to infer much about their properties, the study of albedos, their dependence on wavelength, lighting angle, and variation in time comprises a major part of the astronomical field of photometry
21.
Temperature
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A temperature is an objective comparative measurement of hot or cold. It is measured by a thermometer, several scales and units exist for measuring temperature, the most common being Celsius, Fahrenheit, and, especially in science, Kelvin. Absolute zero is denoted as 0 K on the Kelvin scale, −273.15 °C on the Celsius scale, the kinetic theory offers a valuable but limited account of the behavior of the materials of macroscopic bodies, especially of fluids. Temperature is important in all fields of science including physics, geology, chemistry, atmospheric sciences, medicine. The Celsius scale is used for temperature measurements in most of the world. Because of the 100 degree interval, it is called a centigrade scale.15, the United States commonly uses the Fahrenheit scale, on which water freezes at 32°F and boils at 212°F at sea-level atmospheric pressure. Many scientific measurements use the Kelvin temperature scale, named in honor of the Scottish physicist who first defined it and it is a thermodynamic or absolute temperature scale. Its zero point, 0K, is defined to coincide with the coldest physically-possible temperature and its degrees are defined through thermodynamics. The temperature of zero occurs at 0K = −273. 15°C. For historical reasons, the triple point temperature of water is fixed at 273.16 units of the measurement increment, Temperature is one of the principal quantities in the study of thermodynamics. There is a variety of kinds of temperature scale and it may be convenient to classify them as empirically and theoretically based. Empirical temperature scales are historically older, while theoretically based scales arose in the middle of the nineteenth century, empirically based temperature scales rely directly on measurements of simple physical properties of materials. For example, the length of a column of mercury, confined in a capillary tube, is dependent largely on temperature. Such scales are only within convenient ranges of temperature. For example, above the point of mercury, a mercury-in-glass thermometer is impracticable. A material is of no use as a thermometer near one of its phase-change temperatures, in spite of these restrictions, most generally used practical thermometers are of the empirically based kind. Especially, it was used for calorimetry, which contributed greatly to the discovery of thermodynamics, nevertheless, empirical thermometry has serious drawbacks when judged as a basis for theoretical physics. Theoretically based temperature scales are based directly on theoretical arguments, especially those of thermodynamics, kinetic theory and they rely on theoretical properties of idealized devices and materials
22.
Kelvin
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The kelvin is a unit of measure for temperature based upon an absolute scale. It is one of the seven units in the International System of Units and is assigned the unit symbol K. The kelvin is defined as the fraction 1⁄273.16 of the temperature of the triple point of water. In other words, it is defined such that the point of water is exactly 273.16 K. The Kelvin scale is named after the Belfast-born, Glasgow University engineer and physicist William Lord Kelvin, unlike the degree Fahrenheit and degree Celsius, the kelvin is not referred to or typeset as a degree. The kelvin is the unit of temperature measurement in the physical sciences, but is often used in conjunction with the Celsius degree. The definition implies that absolute zero is equivalent to −273.15 °C, Kelvin calculated that absolute zero was equivalent to −273 °C on the air thermometers of the time. This absolute scale is known today as the Kelvin thermodynamic temperature scale, when spelled out or spoken, the unit is pluralised using the same grammatical rules as for other SI units such as the volt or ohm. When reference is made to the Kelvin scale, the word kelvin—which is normally a noun—functions adjectivally to modify the noun scale and is capitalized, as with most other SI unit symbols there is a space between the numeric value and the kelvin symbol. Before the 13th CGPM in 1967–1968, the unit kelvin was called a degree and it was distinguished from the other scales with either the adjective suffix Kelvin or with absolute and its symbol was °K. The latter term, which was the official name from 1948 until 1954, was ambiguous since it could also be interpreted as referring to the Rankine scale. Before the 13th CGPM, the form was degrees absolute. The 13th CGPM changed the name to simply kelvin. Its measured value was 7002273160280000000♠0.01028 °C with an uncertainty of 60 µK, the use of SI prefixed forms of the degree Celsius to express a temperature interval has not been widely adopted. In 2005 the CIPM embarked on a program to redefine the kelvin using a more experimentally rigorous methodology, the current definition as of 2016 is unsatisfactory for temperatures below 20 K and above 7003130000000000000♠1300 K. In particular, the committee proposed redefining the kelvin such that Boltzmanns constant takes the exact value 6977138065049999999♠1. 3806505×10−23 J/K, from a scientific point of view, this will link temperature to the rest of SI and result in a stable definition that is independent of any particular substance. From a practical point of view, the redefinition will pass unnoticed, the kelvin is often used in the measure of the colour temperature of light sources. Colour temperature is based upon the principle that a black body radiator emits light whose colour depends on the temperature of the radiator, black bodies with temperatures below about 7003400000000000000♠4000 K appear reddish, whereas those above about 7003750000000000000♠7500 K appear bluish
23.
Apparent magnitude
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The apparent magnitude of a celestial object is a number that is a measure of its brightness as seen by an observer on Earth. The brighter an object appears, the lower its magnitude value, the Sun, at apparent magnitude of −27, is the brightest object in the sky. It is adjusted to the value it would have in the absence of the atmosphere, furthermore, the magnitude scale is logarithmic, a difference of one in magnitude corresponds to a change in brightness by a factor of 5√100, or about 2.512. The measurement of apparent magnitudes or brightnesses of celestial objects is known as photometry, apparent magnitudes are used to quantify the brightness of sources at ultraviolet, visible, and infrared wavelengths. An apparent magnitude is measured in a specific passband corresponding to some photometric system such as the UBV system. In standard astronomical notation, an apparent magnitude in the V filter band would be denoted either as mV or often simply as V, the scale used to indicate magnitude originates in the Hellenistic practice of dividing stars visible to the naked eye into six magnitudes. The brightest stars in the sky were said to be of first magnitude, whereas the faintest were of sixth magnitude. Each grade of magnitude was considered twice the brightness of the following grade and this rather crude scale for the brightness of stars was popularized by Ptolemy in his Almagest, and is generally believed to have originated with Hipparchus. This implies that a star of magnitude m is 2.512 times as bright as a star of magnitude m +1 and this figure, the fifth root of 100, became known as Pogsons Ratio. The zero point of Pogsons scale was defined by assigning Polaris a magnitude of exactly 2. However, with the advent of infrared astronomy it was revealed that Vegas radiation includes an Infrared excess presumably due to a disk consisting of dust at warm temperatures. At shorter wavelengths, there is negligible emission from dust at these temperatures, however, in order to properly extend the magnitude scale further into the infrared, this peculiarity of Vega should not affect the definition of the magnitude scale. Therefore, the scale was extrapolated to all wavelengths on the basis of the black body radiation curve for an ideal stellar surface at 11000 K uncontaminated by circumstellar radiation. On this basis the spectral irradiance for the zero magnitude point, with the modern magnitude systems, brightness over a very wide range is specified according to the logarithmic definition detailed below, using this zero reference. In practice such apparent magnitudes do not exceed 30, astronomers have developed other photometric zeropoint systems as alternatives to the Vega system. The AB magnitude zeropoint is defined such that an objects AB, the dimmer an object appears, the higher the numerical value given to its apparent magnitude, with a difference of 5 magnitudes corresponding to a brightness factor of exactly 100. Since an increase of 5 magnitudes corresponds to a decrease in brightness by a factor of exactly 100, each magnitude increase implies a decrease in brightness by the factor 5√100 ≈2.512. Inverting the above formula, a magnitude difference m1 − m2 = Δm implies a brightness factor of F2 F1 =100 Δ m 5 =100.4 Δ m ≈2.512 Δ m
24.
Angular diameter
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The angular diameter or apparent size is an angular measurement describing how large a sphere or circle appears from a given point of view. In the vision sciences it is called the angle and in optics it is the angular aperture. The angular diameter can alternatively be thought of as the angle through which an eye or camera must rotate to look from one side of an apparent circle to the opposite side, Angular radius equals half the angular diameter. When D ≫ d, we have δ ≈ d / D, for practical use, the distinction is only significant for spherical objects that are relatively close, since the small-angle approximation holds for x ≪1, arcsin x ≈ arctan x ≈ x. Estimates of angular diameter may be obtained by holding the hand at right angles to an extended arm. In astronomy the sizes of objects in the sky are given in terms of their angular diameter as seen from Earth. Since these angular diameters are typically small, it is common to present them in arcseconds, an arcsecond is 1/3600th of one degree, and a radian is 180/ π degrees, so one radian equals 3600*180/ π arcseconds, which is about 206265 arcseconds. Therefore, the diameter of an object with physical diameter d at a distance D, expressed in arcseconds, is given by. These objects have a diameter of one arcsecond, an object of diameter 725. The angular diameter of the Sun, from a distance of one light-year, is 0. 03″, the angular diameter 0. 03″ of the Sun given above is approximately the same as that of a person at a distance of the diameter of the Earth. Thus the angular diameter of the Sun is about 250,000 times that of Sirius, the angular diameter of the Sun is also about 250,000 times that of Alpha Centauri A. The angular diameter of the Sun is about the same as that of the Moon, even though Pluto is physically larger than Ceres, when viewed from Earth Ceres has a much larger apparent size. While angular sizes measured in degrees are useful for larger patches of sky, we need much finer units when talking about the size of galaxies. The Moons motion across the sky can be measured in size, approximately 15 degrees every hour. A one-mile-long line painted on the face of the Moon would appear to us to be about one arc-second in length, in astronomy, it is typically difficult to directly measure the distance to an object. But the object may have a physical size and a measurable angular diameter. In that case, the angular diameter formula can be inverted to yield the Angular diameter distance to distant objects as d ≡2 D tan . In non-Euclidean space, such as our universe, the angular diameter distance is only one of several definitions of distance
25.
Moons of Pluto
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The dwarf planet Pluto has five moons down to a detection limit of about 1 km in diameter. In order of distance from Pluto, they are Charon, Styx, Nix, Kerberos, Charon, the largest of the five moons, is mutually tidally locked with Pluto, and is massive enough that Pluto–Charon is sometimes considered a double dwarf planet. The innermost and largest moon, Charon, was discovered by James Christy on 22 June 1978 and this led to a substantial revision in estimates of Plutos size, which had previously assumed that the observed mass and reflected light of the system were all attributable to Pluto alone. The International Astronomical Union officially named these moons Nix and Hydra, Styx, announced on 7 July 2012, was discovered while looking for potential hazards for New Horizons. Charon is about half the diameter of Pluto and is so massive that the barycenter lies between them, approximately 960 km above Plutos surface. Charon and Pluto are also locked, so that they always present the same face toward each other. The IAU General Assembly in August 2006 considered a proposal that Pluto and Charon be reclassified as a double planet, but the proposal was abandoned. Plutos four small moons orbit Pluto at two to four times the distance of Charon, ranging from Styx at 42,700 kilometres to Hydra at 64,800 kilometres from the barycenter of the system and they have nearly circular prograde orbits in the same orbital plane as Charon. All are much smaller than Charon, Nix and Hydra, the two larger, are roughly 42 and 55 kilometers on their longest axis respectively, and Styx and Kerberos are 7 and 12 kilometers respectively. The Pluto system is compact and largely empty. Moons could potentially orbit Pluto at up to 53% of the Hill radius, for example, Psamathe orbits Neptune at 40% of the Hill radius. An intense search conducted by New Horizons confirmed that no larger than 4.5 km in diameter exist at the distances up to 180,000 km from Pluto. Further information is expected as more data from the New Horizons flyby is sent back to Earth. The orbits of the moons are confirmed to be circular and coplanar, with inclinations differing less than 0. 4°, as seen from Earth, these circular orbits appear foreshortened into ellipses depending on Plutos position. The discovery of Nix and Hydra suggested that Pluto could have a ring system, small-body impacts can create debris that can form into a ring system. However, data from a survey by the Advanced Camera for Surveys on the Hubble Space Telescope, by occultation studies. Styx, Nix, and Hydra are thought to be in a 3-body orbital resonance with orbital periods in a ratio of 18,22,33, the ratios should be exact when orbital precession is taken into account. This means that in a recurring cycle there are 11 orbits of Styx for every 9 of Nix and 6 of Hydra, putting Nix and Hydra into a simple 2,3 resonance
26.
Dwarf planet
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A dwarf planet is a planetary-mass object that is neither a planet nor a natural satellite. The International Astronomical Union currently recognizes five dwarf planets, Ceres, Pluto, Haumea, Makemake, another hundred or so known objects in the Solar System are suspected to be dwarf planets. Individual astronomers recognize several of these, and in August 2011 Mike Brown published a list of 390 candidate objects, Stern states that there are more than a dozen known dwarf planets. Only two of these bodies, Ceres and Pluto, have observed in enough detail to demonstrate that they actually fit the IAUs definition. The IAU accepted Eris as a dwarf planet because it is more massive than Pluto and they subsequently decided that unnamed trans-Neptunian objects with an absolute magnitude brighter than +1 are to be named under the assumption that they are dwarf planets. The classification of bodies in other systems with the characteristics of dwarf planets has not been addressed. Starting in 1801, astronomers discovered Ceres and other bodies between Mars and Jupiter which were for some decades considered to be planets. Between then and around 1851, when the number of planets had reached 23, astronomers started using the asteroid for the smaller bodies. With the discovery of Pluto in 1930, most astronomers considered the Solar System to have nine planets and it was roughly one-twentieth the mass of Mercury, which made Pluto by far the smallest planet. Although it was more than ten times as massive as the largest object in the asteroid belt, Ceres. In the 1990s, astronomers began to find objects in the region of space as Pluto. Many of these shared several of Plutos key orbital characteristics, and Pluto started being seen as the largest member of a new class of objects and this led some astronomers to stop referring to Pluto as a planet. Several terms, including subplanet and planetoid, started to be used for the now known as dwarf planets. By 2005, three trans-Neptunian objects comparable in size to Pluto had been reported and it became clear that either they would also have to be classified as planets, or Pluto would have to be reclassified. Astronomers were also confident that more objects as large as Pluto would be discovered, Eris was discovered in January 2005, it was thought to be slightly larger than Pluto, and some reports informally referred to it as the tenth planet. As a consequence, the became a matter of intense debate during the IAU General Assembly in August 2006. The IAUs initial draft proposal included Charon, Eris, and Ceres in the list of planets, dropping Charon from the list, the new proposal also removed Pluto, Ceres, and Eris, because they have not cleared their orbits. The IAUs final Resolution 5A preserved this three-category system for the bodies orbiting the Sun
27.
United States Naval Observatory
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The USNO operates the Master Clock, which provides precise time to the GPS satellite constellation run by the United States Air Force. The USNO performs radio VLBI-based positions of quasars with numerous global collaborators, aside from its scientific mission, a house located within the Naval Observatory complex serves as the official residence of the Vice President of the United States. President John Quincy Adams, who in 1825 signed the bill for the creation of an observatory just before leaving presidential office, had intended for it to be called the National Observatory. The names National Observatory and Naval Observatory were both used for 10 years, until a ruling was passed to use the latter. Adams had made protracted efforts to bring astronomy to a level at that time. He spent many nights at the observatory, watching and charting the stars, established by the order of the United States Secretary of the Navy John Branch on 6 December 1830 as the Depot of Charts and Instruments, the Observatory rose from humble beginnings. Placed under the command of Lieutenant Louis M. Goldsborough, with an budget of $330, its primary function was the restoration, repair. It was made into an observatory in 1842 via a federal law. Lieutenant James Melville Gilliss was put in charge of obtaining the instruments needed, lt. Gilliss visited the principal observatories of Europe with the mission to purchase telescopes and scientific devices and books. The observatorys primary mission was to care for the United States Navys marine chronometers, charts and it calibrated ships chronometers by timing the transit of stars across the meridian. These facilities were listed on the National Register of Historic Places in 2017, the first superintendent was Navy Commander Matthew Fontaine Maury. Maury had the worlds first vulcanized time ball, created to his specifications by Charles Goodyear for the U. S. Observatory and it was the first time ball in the United States, being placed into service in 1845, and the 12th in the world. Maury kept accurate time by the stars and planets, the time ball was dropped every day except Sunday precisely at the astronomically defined moment of Mean Solar Noon, enabling all ships and civilians to know the exact time. Time was also sold to the railroads and was used in conjunction with railroad chronometers to schedule American rail transport, early in the 20th century, the Arlington Time Signal broadcast this service to wireless receivers. In 1849 the Nautical Almanac Office was established in Cambridge, Massachusetts as a separate organization and it was moved to Washington, D. C. in 1866, colocating with the U. S. Naval Observatory in 1893. On September 20,1894, the NAO became a branch of USNO, the astronomical measurements taken of the transit of Venus by a number of countries since 1639 resulted in a progressively more accurate definition of the AU. Relying heavily on methods, the naval observers returned 350 photographic plates in 1874. This calculated distance was a significant improvement over several previous estimates, the telescope used for the discovery of the Moons of Mars was the 26-inch refractor, then located at Foggy Bottom
28.
Washington, D.C.
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Washington, D. C. formally the District of Columbia and commonly referred to as Washington, the District, or simply D. C. is the capital of the United States. The signing of the Residence Act on July 16,1790, Constitution provided for a federal district under the exclusive jurisdiction of the Congress and the District is therefore not a part of any state. The states of Maryland and Virginia each donated land to form the federal district, named in honor of President George Washington, the City of Washington was founded in 1791 to serve as the new national capital. In 1846, Congress returned the land ceded by Virginia, in 1871. Washington had an population of 681,170 as of July 2016. Commuters from the surrounding Maryland and Virginia suburbs raise the population to more than one million during the workweek. The Washington metropolitan area, of which the District is a part, has a population of over 6 million, the centers of all three branches of the federal government of the United States are in the District, including the Congress, President, and Supreme Court. Washington is home to national monuments and museums, which are primarily situated on or around the National Mall. The city hosts 176 foreign embassies as well as the headquarters of international organizations, trade unions, non-profit organizations, lobbying groups. A locally elected mayor and a 13‑member council have governed the District since 1973, However, the Congress maintains supreme authority over the city and may overturn local laws. D. C. residents elect a non-voting, at-large congressional delegate to the House of Representatives, the District receives three electoral votes in presidential elections as permitted by the Twenty-third Amendment to the United States Constitution, ratified in 1961. Various tribes of the Algonquian-speaking Piscataway people inhabited the lands around the Potomac River when Europeans first visited the area in the early 17th century, One group known as the Nacotchtank maintained settlements around the Anacostia River within the present-day District of Columbia. Conflicts with European colonists and neighboring tribes forced the relocation of the Piscataway people, some of whom established a new settlement in 1699 near Point of Rocks, Maryland. 43, published January 23,1788, James Madison argued that the new government would need authority over a national capital to provide for its own maintenance. Five years earlier, a band of unpaid soldiers besieged Congress while its members were meeting in Philadelphia, known as the Pennsylvania Mutiny of 1783, the event emphasized the need for the national government not to rely on any state for its own security. However, the Constitution does not specify a location for the capital, on July 9,1790, Congress passed the Residence Act, which approved the creation of a national capital on the Potomac River. The exact location was to be selected by President George Washington, formed from land donated by the states of Maryland and Virginia, the initial shape of the federal district was a square measuring 10 miles on each side, totaling 100 square miles. Two pre-existing settlements were included in the territory, the port of Georgetown, Maryland, founded in 1751, many of the stones are still standing
29.
United States Naval Observatory Flagstaff Station
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The United States Naval Observatory Flagstaff Station, is an astronomical observatory near Flagstaff, Arizona, USA. It is the national dark-sky observing facility under the United States Naval Observatory, NOFS and USNO combine as the Celestial Reference Frame manager for the U. S. Secretary of Defense. NOFS science supports every aspect of astronomy to some level, providing national support. Work at NOFS covers the gamut of astrometry and astrophysics in order to facilitate its production of accurate/precise astronomical catalogs, multiple observations of each object may themselves take weeks, months or years, by themselves. The United States Naval Observatory, Flagstaff Station celebrated its 50th anniversary of the move there from Washington, dr. John Hall, Director of the Naval Observatorys Equatorial Division from 1947, founded NOFS. Dr. Art Hoag became its first director in 1955, both later were to become directors of nearby Lowell Observatory. NOFS remains active in supporting regional dark skies, both to support its national mission, and to promote and protect a national resource legacy for generations of humans to come. Indeed, despite a history, NOFS has a rich heritage which is derived from its parent organization, USNO. Navy since it saw first light in 1964 and this status will change when the NPOI four 1. 8-meter telescopes see their own first light in the near future. KSAR rides in the arms of a fork mount. The telescope is used in both the spectrum, and in the near infrared, the latter using a sub-30-Kelvin, helium-refrigerated, InSb camera. In 1978, the 1. 55-m telescope was used to discover the moon of dwarf planet Pluto, the Charon discovery led to mass calculations which ultimately revealed how tiny Pluto was, and eventually caused the IAU to reclassify Pluto as a dwarf planet. The 1. 55-meter telescope was used to observe and track NASAs Deep Impact Spacecraft, as it navigated to a successful inter-planetary impact with the celebrated Comet 9p/Tempel. The 61 dome is located on NOFS grounds, with support. The large vacuum coating chamber facility is located in this complex. A dielectric coating capability has also been demonstrated, large optics and telescope components can be moved about NOFS using its suite of cranes, lifts, cargo elevators and specialized carts. The KSAR Telescopes 60-foot diameter steel dome is large for the telescopes aperture. It uses a very wide 2-shutter, vertical slit. 6-meters, by using fast, however, the 61-inch telescope remains unique in its ability to operationally conduct both very high-accuracy relative astrometry to the milliarcsecond level, and close-separation, PSF photometry
30.
Barycenter
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The barycenter is the center of mass of two or more bodies that are orbiting each other, or the point around which they both orbit. It is an important concept in such as astronomy and astrophysics. The distance from a center of mass to the barycenter can be calculated as a simple two-body problem. In cases where one of the two objects is more massive than the other, the barycenter will typically be located within the more massive object. Rather than appearing to orbit a center of mass with the smaller body. This is the case for the Earth–Moon system, where the barycenter is located on average 4,671 km from the Earths center, when the two bodies are of similar masses, the barycenter will generally be located between them and both bodies will follow an orbit around it. This is the case for Pluto and Charon, as well as for many binary asteroids and it is also the case for Jupiter and the Sun, despite the thousandfold difference in mass, due to the relatively large distance between them. In astronomy, barycentric coordinates are non-rotating coordinates with the origin at the center of mass of two or more bodies, the International Celestial Reference System is a barycentric one, based on the barycenter of the Solar System. In geometry, the barycenter is synonymous with centroid, the geometric center of a two-dimensional shape. The barycenter is one of the foci of the orbit of each body. This is an important concept in the fields of astronomy and astrophysics. If a is the distance between the centers of the two bodies, r1 is the axis of the primarys orbit around the barycenter. When the barycenter is located within the massive body, that body will appear to wobble rather than to follow a discernible orbit. The following table sets out some examples from the Solar System, figures are given rounded to three significant figures. If Jupiter had Mercurys orbit, the Sun–Jupiter barycenter would be approximately 55,000 km from the center of the Sun, but even if the Earth had Eris orbit, the Sun–Earth barycenter would still be within the Sun. To calculate the motion of the Sun, you would need to sum all the influences from all the planets, comets, asteroids. If all the planets were aligned on the side of the Sun. The calculations above are based on the distance between the bodies and yield the mean value r1
31.
Tholin
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Tholins are a class of heteropolymer molecules formed by solar ultraviolet irradiation of simple organic compounds such as methane or ethane, often in combination with nitrogen. They usually have a reddish-brown appearance, however, we have recently succeeded, through sequential and non-sequential pyrolysis followed by gas chromatography-mass spectrometry in determining something of the composition of this material. It is clearly not a repetition of the same monomeric unit—and some other term is needed. We propose, as a descriptive term, ‘tholins’, although we were tempted by the phrase ‘star-tar’. Tholins are not one specific compound but rather are descriptive of a spectrum of molecules that give a reddish, as illustrated to the right, tholins are believed to form through a chain of chemical reactions. This begins with the dissociation and ionization of molecular nitrogen and methane by energetic particles and this is followed by the formation of ethylene, ethane, acetylene, hydrogen cyanide, and other small simple molecules and small positive ions. These atmospherically-derived substances are distinct from ice tholin, which is formed instead by irradiation of clathrates of water, the surfaces of comets, centaurs, and many icy moons and Kuiper-belt objects in the outer solar system are rich in deposits of tholins. Titan tholins are nitrogen-rich organic substances produced by the irradiation of the mixtures of nitrogen and methane found in the atmosphere. Titans atmosphere is 98. 4% nitrogen and the remaining 1. 6% composed of methane, in the case of Titan, the haze and orange-red color of its atmosphere is thought to be caused by the presence of tholins. Neptunes moon Triton is observed to have the color characteristic of tholins. Tritons atmosphere is 99. 9% nitrogen and 0. 1% methane, tholins also occur on the dwarf planet Pluto and its moon Charon and are responsible for their red colors as well as the blue tint of Plutos atmosphere. Tholins have also detected on the plutino Ixion. The HR4796 system is approximately 220 light years from Earth, some researchers have speculated that Earth may have been seeded by organic compounds early in its development by tholin-rich comets, providing the raw material necessary for life to develop. Tholins do not exist naturally on present-day Earth due to the character of the free oxygen component of its atmosphere ever since the Great Oxygenation Event around 2.4 billion years ago. Tholins can act as a screen for protecting planetary surfaces from ultraviolet radiation. A wide variety of bacteria are able to use tholins as their sole source of carbon. Tholins could have been the first microbial food for heterotrophic microorganisms before autotrophy evolved
32.
Organic compound
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An organic compound is virtually any chemical compound that contains carbon, although a consensus definition remains elusive and likely arbitrary. Organic compounds are rare terrestrially, but of importance because all known life is based on organic compounds. The most basic petrochemicals are considered the building blocks of organic chemistry, for historical reasons discussed below, a few types of carbon-containing compounds, such as carbides, carbonates, simple oxides of carbon, and cyanides are considered inorganic. The distinction between organic and inorganic compounds, while useful in organizing the vast subject of chemistry. Organic chemistry is the science concerned with all aspects of organic compounds, Organic synthesis is the methodology of their preparation. The word organic is historical, dating to the 1st century, for many centuries, Western alchemists believed in vitalism. This is the theory that certain compounds could be synthesized only from their classical elements—earth, water, air, vitalism taught that these organic compounds were fundamentally different from the inorganic compounds that could be obtained from the elements by chemical manipulation. Vitalism survived for a while even after the rise of modern atomic theory and it first came under question in 1824, when Friedrich Wöhler synthesized oxalic acid, a compound known to occur only in living organisms, from cyanogen. A more decisive experiment was Wöhlers 1828 synthesis of urea from the inorganic salts potassium cyanate, urea had long been considered an organic compound, as it was known to occur only in the urine of living organisms. Wöhlers experiments were followed by others, in which increasingly complex organic substances were produced from inorganic ones without the involvement of any living organism. Even though vitalism has been discredited, scientific nomenclature retains the distinction between organic and inorganic compounds, still, even the broadest definition requires excluding alloys that contain carbon, including steel. The C-H definition excludes compounds that are considered organic, neither urea nor oxalic acid is organic by this definition, yet they were two key compounds in the vitalism debate. The IUPAC Blue Book on organic nomenclature specifically mentions urea and oxalic acid, other compounds lacking C-H bonds but traditionally considered organic include benzenehexol, mesoxalic acid, and carbon tetrachloride. Mellitic acid, which contains no C-H bonds, is considered an organic substance in Martian soil. The C-H bond-only rule also leads to somewhat arbitrary divisions in sets of carbon-fluorine compounds, for example, CF4 would be considered by this rule to be inorganic, whereas CF3H would be organic. Organic compounds may be classified in a variety of ways, one major distinction is between natural and synthetic compounds. Another distinction, based on the size of organic compounds, distinguishes between small molecules and polymers, natural compounds refer to those that are produced by plants or animals. Many of these are extracted from natural sources because they would be more expensive to produce artificially
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Macromolecule
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A macromolecule is a very large molecule, such as protein, commonly created by polymerization of smaller subunits. They are typically composed of thousands of atoms or more, the most common macromolecules in biochemistry are biopolymers and large non-polymeric molecules. Synthetic macromolecules include common plastics and synthetic fibres as well as materials such as carbon nanotubes. The term macromolecule was coined by Nobel laureate Hermann Staudinger in the 1920s, usage of the term to describe large molecules varies among the disciplines. According to the standard IUPAC definition, the term macromolecule as used in science refers only to a single molecule. For example, a polymeric molecule is appropriately described as a macromolecule or polymer molecule rather than a polymer. Because of their size, macromolecules are not conveniently described in terms of stoichiometry alone, the structure of simple macromolecules, such as homopolymers, may be described in terms of the individual monomer subunit and total molecular mass. Complicated biomacromolecules, on the hand, require multi-faceted structural description such as the hierarchy of structures used to describe proteins. In British English. Macromolecules often have physical properties that do not occur for smaller molecules. For example, DNA in a solution can be simply by sucking the solution through an ordinary straw because the physical forces on the molecule can overcome the strength of its covalent bonds. The 1964 edition of Linus Paulings College Chemistry asserted that DNA in nature is never longer than about 5,000 base pairs and this error arose because biochemists were inadvertently breaking their samples into fragments. In fact, the DNA of chromosomes can be hundreds of millions of base pairs long, another common macromolecular property that does not characterize smaller molecules is their relative insolubility in water and similar solvents, instead forming colloids. Many require salts or particular ions to dissolve in water, similarly, many proteins will denature if the solute concentration of their solution is too high or too low. High concentrations of macromolecules in a solution can alter the rates and equilibrium constants of the reactions of other macromolecules and this comes from macromolecules excluding other molecules from a large part of the volume of the solution, thereby increasing the effective concentrations of these molecules. All living organisms are dependent on three essential biopolymers for their functions, DNA, RNA and Proteins. Each of these molecules is required for life since each plays a distinct, the simple summary is that DNA makes RNA, and then RNA makes proteins. DNA, RNA and proteins all consist of a structure of related building blocks. In general, they are all unbranched polymers, and so can be represented in the form of a string
34.
Life
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Various forms of life exist, such as plants, animals, fungi, protists, archaea, and bacteria. The criteria can at times be ambiguous and may or may not define viruses, viroids, biology is the primary science concerned with the study of life, although many other sciences are involved. The definition of life is controversial, the current definition is that organisms maintain homeostasis, are composed of cells, undergo metabolism, can grow, adapt to their environment, respond to stimuli, and reproduce. However, many other definitions have been proposed, and there are some borderline cases. Modern definitions are more complex, with input from a diversity of scientific disciplines, biophysicists have proposed many definitions based on chemical systems, there are also some living systems theories, such as the Gaia hypothesis, the idea that the Earth itself is alive. Another theory is that life is the property of systems, and yet another is elaborated in complex systems biology. Abiogenesis describes the process of life arising from non-living matter. Properties common to all organisms include the need for certain chemical elements to sustain biochemical functions. Life on Earth first appeared as early as 4.28 billion years ago, soon after ocean formation 4.41 billion years ago, Earths current life may have descended from an RNA world, although RNA-based life may not have been the first. The mechanism by which began on Earth is unknown, though many hypotheses have been formulated and are often based on the Miller–Urey experiment. The earliest known forms are microfossils of bacteria. In July 2016, scientists reported identifying a set of 355 genes believed to be present in the last universal ancestor of all living organisms. Since its primordial beginnings, life on Earth has changed its environment on a time scale. To survive in most ecosystems, life must often adapt to a range of conditions. Some microorganisms, called extremophiles, thrive in physically or geochemically extreme environments that are detrimental to most other life on Earth, Aristotle was the first person to classify organisms. Later, Carl Linnaeus introduced his system of nomenclature for the classification of species. Eventually new groups and categories of life were discovered, such as cells and microorganisms, cells are sometimes considered the smallest units and building blocks of life. There are two kinds of cells, prokaryotic and eukaryotic, both of which consist of cytoplasm enclosed within a membrane and contain many such as proteins
35.
Nitrogen
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Nitrogen is a chemical element with symbol N and atomic number 7. It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772, although Carl Wilhelm Scheele and Henry Cavendish had independently done so at about the same time, Rutherford is generally accorded the credit because his work was published first. Nitrogen is the lightest member of group 15 of the periodic table, the name comes from the Greek πνίγειν to choke, directly referencing nitrogens asphyxiating properties. It is an element in the universe, estimated at about seventh in total abundance in the Milky Way. At standard temperature and pressure, two atoms of the element bind to form dinitrogen, a colourless and odorless diatomic gas with the formula N2, dinitrogen forms about 78% of Earths atmosphere, making it the most abundant uncombined element. Nitrogen occurs in all organisms, primarily in amino acids, in the nucleic acids, the human body contains about 3% nitrogen by mass, the fourth most abundant element in the body after oxygen, carbon, and hydrogen. The nitrogen cycle describes movement of the element from the air, into the biosphere and organic compounds, many industrially important compounds, such as ammonia, nitric acid, organic nitrates, and cyanides, contain nitrogen. The extremely strong bond in elemental nitrogen, the second strongest bond in any diatomic molecule. Synthetically produced ammonia and nitrates are key industrial fertilisers, and fertiliser nitrates are key pollutants in the eutrophication of water systems. Apart from its use in fertilisers and energy-stores, nitrogen is a constituent of organic compounds as diverse as Kevlar used in high-strength fabric, Nitrogen is a constituent of every major pharmacological drug class, including antibiotics. Many notable nitrogen-containing drugs, such as the caffeine and morphine or the synthetic amphetamines. Nitrogen compounds have a long history, ammonium chloride having been known to Herodotus. They were well known by the Middle Ages, alchemists knew nitric acid as aqua fortis, as well as other nitrogen compounds such as ammonium salts and nitrate salts. The mixture of nitric and hydrochloric acids was known as aqua regia, celebrated for its ability to dissolve gold, the discovery of nitrogen is attributed to the Scottish physician Daniel Rutherford in 1772, who called it noxious air. Though he did not recognise it as a different chemical substance, he clearly distinguished it from Joseph Blacks fixed air. The fact that there was a component of air that does not support combustion was clear to Rutherford, Nitrogen was also studied at about the same time by Carl Wilhelm Scheele, Henry Cavendish, and Joseph Priestley, who referred to it as burnt air or phlogisticated air. Nitrogen gas was inert enough that Antoine Lavoisier referred to it as air or azote, from the Greek word άζωτικός. In an atmosphere of nitrogen, animals died and flames were extinguished
36.
Atmosphere of Pluto
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The atmosphere of Pluto is the tenuous layer of gases surrounding Pluto. It consists mainly of nitrogen, with amounts of methane and carbon monoxide. It contains layered haze, probably consisting of compounds which form from these gases due to high-energy radiation. The atmosphere of Pluto is notable for its strong and not completely clear seasonal changes caused by peculiarities of the orbital and axial rotation of Pluto. Surface pressure of the atmosphere of Pluto, measured by New Horizons in 2015, is about 1 Pa, temperature on the surface is 40 to 60 K, but it quickly grows with altitude due to methane-generated greenhouse effect. Near the altitude 30 km it reaches 110 K, and then slowly decreases, Pluto is the only trans-Neptunian object with a known atmosphere. Its closest analog is the atmosphere of Triton, although in some aspects it resembles even the atmosphere of Mars, the atmosphere of Pluto has been studied since the 1980s by way of earth-based observation of occultations of stars by Pluto and spectroscopy. In 2015, it was studied from a distance by the spacecraft New Horizons. The main component of the atmosphere of Pluto is nitrogen, content of methane, according to measurements by New Horizons, is 0. 25%. For carbon monoxide, the Earth-based estimates are 0. 025–0. 15% and 0. 05–0. 075%, under influence of high-energy cosmic radiation, these gases react to form more complex compounds, including ethane, ethylene, acetylene, heavier hydrocarbons and nitriles and hydrogen cyanide. These compounds slowly precipitate on the surface, probably, they also include tholins, which are responsible for the brown color of Pluto. The most volatile compound of the atmosphere of Pluto is nitrogen, the second is carbon monoxide, the indicator of volatility is saturated vapor pressure. At temperature 40 K it is about 10 Pa for nitrogen,1 Pa for carbon monoxide and 0.001 Pa for methane and it quickly increases with temperature, and at 60 K approaches to 10000 Pa,3000 Pa and 10 Pa respectively. For heavier-than-methane hydrocarbons, water, ammonia, carbon dioxide and hydrogen cyanide, this pressure remains negligibly low, but actually concentration of, at least, methane, does not depends noticeably of height, longitude and time. But temperature dependence of volatility of methane and nitrogen suggest that concentration of methane will decrease during moving of Pluto further from the Sun, reasons of this discrepancy are unknown. It can be due to existence of separate patches of relatively clean methane ice, seasonal and orbital changes of insolation results in migration of surface ices, they sublimate in some places and condensate in another. According to some estimates, it gives meter-sized changes of their thickness and this results in appreciable changes of brightness and color of Pluto. Methane and carbon monoxide, despite their low abundance, are significant for thermal structure of the atmosphere, methane is a strong heating agent and carbon monoxide is a cooling one
37.
Photographic plate
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Photographic plates preceded photographic film as a capture medium in photography. The light-sensitive emulsion of silver salts was coated on a plate, typically thinner than common window glass. Glass plates were far superior to film for research-quality imaging because they were stable and less likely to bend or distort. Early plates used the wet collodion process, the wet plate process was replaced late in the 19th century by gelatin dry plates. Glass plate photographic material largely faded from the market in the early years of the 20th century, as more convenient. Workshops on the use of glass plate photography as a medium or for artistic use are still being conducted. A number of observatories, including Harvard College and Sonneberg, maintain large archives of photographic plates, many solar system objects were discovered by using photographic plates, superseding earlier visual methods. Discovery of minor planets using photographic plates was pioneered by Max Wolf beginning with his discovery of 323 Brucia in 1891, the first natural satellite discovered using photographic plates was Phoebe in 1898. Glass-backed plates, rather than film, were used in astronomy because they do not shrink or deform noticeably in the development process or under environmental changes. Photographic plates were also an important tool in early high-energy physics, Photographic emulsions were originally coated on thin glass plates for imaging with electron microscopes, which provided a more rigid, stable and flatter plane compared to plastic films. Beginning in the 1970s, high-contrast, fine grain emulsions coated on thicker plastic films manufactured by Kodak, Ilford and these films have largely been replaced by digitally imaging technologies. The earliest flexible films of the late 1880s were sold for use in medium-format cameras. The plastic was not of high optical quality and tended to curl. Initially, a transparent plastic base was more expensive to produce than glass, quality was eventually improved, manufacturing costs came down, and most amateurs gladly abandoned plates for films. After large-format high quality cut films for professional photographers were introduced in the late 1910s, CCD cameras have several advantages over glass plates, including high efficiency, linear light response, and simplified image acquisition and processing. The manufacture of plates has been discontinued by Kodak, Agfa. In the realm of traditional photography, a number of historical process enthusiasts make their own wet or dry plates from raw materials. Several institutions have established archives to preserve photographic plates and prevent their valuable historical information from being lost, the emulsion on the plate can deteriorate
38.
International Astronomical Union
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The International Astronomical Union is an international association of professional astronomers, at the PhD level and beyond, active in professional research and education in astronomy. Among other activities, it acts as the recognized authority for assigning designations to celestial bodies. The IAU is a member of the International Council for Science and its main objective is to promote and safeguard the science of astronomy in all its aspects through international cooperation. The IAU maintains friendly relations with organizations that include amateur astronomers in their membership, the IAU has its head office on the second floor of the Institut dAstrophysique de Paris in the 14th arrondissement of Paris. The IAU is also responsible for the system of astronomical telegrams which are produced and distributed on its behalf by the Central Bureau for Astronomical Telegrams, the Minor Planet Center also operates under the IAU, and is a clearinghouse for all non-planetary or non-moon bodies in the Solar System. The Working Group for Meteor Shower Nomenclature and the Meteor Data Center coordinate the nomenclature of meteor showers, the IAU was founded on July 28,1919, at the Constitutive Assembly of the International Research Council held in Brussels, Belgium. The 7 initial member states were Belgium, Canada, France, Great Britain, Greece, Japan, the first executive committee consisted of Benjamin Baillaud, Alfred Fowler, and four vice presidents, William Campbell, Frank Dyson, Georges Lecointe, and Annibale Riccò. Thirty-two Commissions were appointed at the Brussels meeting and focused on topics ranging from relativity to minor planets, the reports of these 32 Commissions formed the main substance of the first General Assembly, which took place in Rome, Italy, May 2–10,1922. By the end of the first General Assembly, ten nations had joined the Union. Although the Union was officially formed eight months after the end of World War I, the first 50 years of the Unions history are well documented. Subsequent history is recorded in the form of reminiscences of past IAU Presidents, twelve of the fourteen past General Secretaries in the period 1964-2006 contributed their recollections of the Unions history in IAU Information Bulletin No.100. Six past IAU Presidents in the period 1976–2003 also contributed their recollections in IAU Information Bulletin No.104, the IAU includes a total of 12,664 individual members who are professional astronomers from 96 countries worldwide. 83% of all members are male, while 17% are female, among them the unions current president. Membership also includes 79 national members, professional astronomical communities representing their countrys affiliation with the IAU, the sovereign body of the IAU is its General Assembly, which comprises all members. The Assembly determines IAU policy, approves the Statutes and By-Laws of the Union, the right to vote on matters brought before the Assembly varies according to the type of business under discussion. On budget matters, votes are weighted according to the subscription levels of the national members. A second category vote requires a turnout of at least two-thirds of national members in order to be valid, an absolute majority is sufficient for approval in any vote, except for Statute revision which requires a two-thirds majority. An equality of votes is resolved by the vote of the President of the Union, since 1922, the IAU General Assembly meets every three years, with the exception of the period between 1938 and 1948, due to World War II
39.
Light curve
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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
. Bibcode:2006AJ....132..290B. doi:10.1086/504422.
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