1.
Biela's Comet
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Bielas Comet or Comet Biela was a periodic Jupiter-family comet first recorded in 1772 by Montaigne and Messier and finally identified as periodic in 1826 by Wilhelm von Biela. It was subsequently observed to split in two and has not been seen since 1852, as a result it is currently considered to have been destroyed, although remnants appeared to have survived for some time as a meteor shower, the Andromedids. The comet was first recorded on 8 March 1772 by Jacques Leibax Montaigne and it was also recorded in 1805 by Jean-Louis Pons, but was not recognized as the same object.6 years. At the time it was only the third comet known to be periodic, after comets Halley, a third claim was made by Thomas Clausen, who had independently linked the comets. The comet appeared as predicted during its 1832 apparition, when it was first recovered by John Herschel on 24 September. Despite this, the fact that Bielas Comet was the comet known to intersect the Earths orbit was to make it of particular interest. The 1839 apparition was extremely unfavourable and no observations were made, the comet was recovered on November 26,1845, by Francesco de Vico. Initially a small, faint nebulosity, subsequent observations showed that something remarkable had happened to it, matthew Fontaine Maury, observing on 14 January 1846, noted that an apparent companion was located 1 arc minute north of the comet. After this announcement many astronomers began observing the comet, and noted that the two alternated in brightness, developing parallel tails as they approached perihelion. In 1852 the comet was recovered more or less as predicted, with Comet A being recovered first. Comet B was finally relocated on September 16, and once again both nuclei alternated in brightness during the period of observation, a was last detected on this apparition on September 26 and B on September 29, in both cases by Otto Wilhelm Struve. Neither part could be found on their periodic returns in 1859,1865. However, on November 27,1872, a brilliant meteor shower was observed radiating from the part of the sky where the comet had been predicted to cross in September 1872 and this was the date when Earth intersected the comets trajectory. These meteors became known as the Andromedids or Bielids and it seems apparent that they were produced by the breakup of the comet. The meteors were seen again on subsequent occasions for the rest of the 19th century, there were, however, inconclusive observations during the 1865 and 1872 returns. Charles Talmage, using ephemerides provided by John Russell Hind, claimed to have observed a nebulous object in approximately the right position in November 1865. Despite the apparent destruction of the comet, there were a number of searches for it during the later 20th century and it has been calculated that the mass of the debris left in the Andromedid meteor stream is still much less than the total mass of the comet. Given that it is likely that the main mass loss occurred near aphelion before the 1845 apparition
2.
Comet
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A comet is an icy small Solar System body that, when passing close to the Sun, warms and begins to evolve gasses, a process called outgassing. This produces an atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred metres to tens of kilometres across and are composed of collections of ice, dust. The coma may be up to 15 times the Earths diameter, if sufficiently bright, a comet may be seen from the Earth without the aid of a telescope and may subtend an arc of 30° across the sky. Comets have been observed and recorded since ancient times by many cultures, Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star. Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars, hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space. The appearance of a comet is called an apparition, Comets are distinguished from asteroids by the presence of an extended, gravitationally unbound atmosphere surrounding their central nucleus. This atmosphere has parts termed the coma and the tail, however, extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids. Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System, the discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets. As of November 2014 there are 5,253 known comets, however, this represents only a tiny fraction of the total potential comet population, as the reservoir of comet-like bodies in the outer Solar System is estimated to be one trillion. Roughly one comet per year is visible to the eye, though many of those are faint. Particularly bright examples are called Great Comets, the word comet derives from the Old English cometa from the Latin comēta or comētēs. That, in turn, is a latinisation of the Greek κομήτης, Κομήτης was derived from κομᾶν, which was itself derived from κόμη and was used to mean the tail of a comet. The astronomical symbol for comets is ☄, consisting of a disc with three hairlike extensions. The solid, core structure of a comet is known as the nucleus, cometary nuclei are composed of an amalgamation of rock, dust, water ice, and frozen gases such as carbon dioxide, carbon monoxide, methane, and ammonia. As such, they are described as dirty snowballs after Fred Whipples model
3.
Perihelion and aphelion
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The perihelion is the point in the orbit of a celestial body where it is nearest to its orbital focus, generally a star. It is the opposite of aphelion, which is the point in the orbit where the body is farthest from its focus. The word perihelion stems from the Ancient Greek words peri, meaning around or surrounding, aphelion derives from the preposition apo, meaning away, off, apart. According to Keplers first law of motion, all planets, comets. Hence, a body has a closest and a farthest point from its parent object, that is, a perihelion. Each extreme is known as an apsis, orbital eccentricity measures the flatness of the orbit. Because of the distance at aphelion, only 93. 55% of the solar radiation from the Sun falls on a given area of land as does at perihelion. However, this fluctuation does not account for the seasons, as it is summer in the northern hemisphere when it is winter in the southern hemisphere and vice versa. Instead, seasons result from the tilt of Earths axis, which is 23.4 degrees away from perpendicular to the plane of Earths orbit around the sun. Winter falls on the hemisphere where sunlight strikes least directly, and summer falls where sunlight strikes most directly, in the northern hemisphere, summer occurs at the same time as aphelion. Despite this, there are larger land masses in the northern hemisphere, consequently, summers are 2.3 °C warmer in the northern hemisphere than in the southern hemisphere under similar conditions. Apsis Ellipse Solstice Dates and times of Earths perihelion and aphelion, 2000–2025 from the United States Naval Observatory
4.
Lost minor planet
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Lost minor planets are minor planets that observers lose track of due to too short an observation arc to accurately predict the future location of the minor planet. Many of the asteroids that were discovered early were lost and rediscovered in the 1980s and 1990s, some minor planets and comets discovered in previous decades were lost because the observational data obtained was insufficient to determine a reliable orbit. Without this information, astronomers would not know where to look for the object at future dates, occasionally, a newly discovered object turns out to be a rediscovery of a previously lost object. This can be determined by calculating the new objects orbit backwards and this may greatly extend the observation arc, thus fixing the orbit much more precisely. For lost comets the back orbit calculations are especially tricky because of forces that can affect their orbits. However, Brian G. Marsden has specialized in calculating such nongravitational forces, notably, he successfully predicted the 1992 return of the once-lost periodic comet Swift–Tuttle. This is a selection of some early lost or notable asteroids with their discovery and rediscovery dates. The true number of lost asteroids may be over 150,000, there are also about 30,000 unnumbered bodies with a condition code of U = 9, indicating the highest possible uncertainty of their orbit determination. Many of these bodies have been observed if not decades ago. There are also more than a thousand objects with an observation arc of one or two days only. There are earlier examples also, such as 132 Aethra, which was lost between 1873 and 1922, leif Kahl Kristensen at the University of Aarhus rediscovered 452 Hamiltonia and 1537 Transylvania, along with numerous other small objects, in 1981. He named it China, or 中華 Zhōnghuá, however, this asteroid was not observed beyond its initial appearance and a precise orbit could not be calculated. However, in 1986, the newly discovered object 1986 QK1 was confirmed to be a rediscovery of the original 1928 UF, and this object was named 3789 Zhongguo, the near-Earth asteroid 1950 DA was discovered on 23 February 1950 by Carl Wirtanen at Lick Observatory. It was observed for 17 days and then lost, since not enough observations were made to allow its orbit to be plotted and it was then rediscovered on 31 December 2000. The chance it will impact Earth on 16 March 2880 is about 1 in 4,000,7796 Járacimrman was discovered at the Czech Kleť Observatory on 16 January 1996 by Zdeněk Moravec and was designated 1996 BG. It was observed until April 1996 and then in June and July 1997, recently lost minor planets 2007 WD5 is a 50 m Apollo-class NEO and a Mars-crosser discovered on 20 November 2007, by Andrea Boattini of the Catalina Sky Survey. Early observations of 2007 WD5 caused excitement amongst the community when it was estimated as having as high as a 1 in 25 chance of colliding with Mars on 30 January 2008. However, by 9 January 2008 additional observations allowed NASAs Near Earth Object Program to reduce the uncertainty region resulting in only a 1-in-10,000 chance of impact,2007 WD5 most likely passed Mars at a distance of 6.5 Mars radii
5.
Comet nucleus
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The nucleus is the solid, central part of a comet, popularly termed a dirty snowball or an icy dirtball. A cometary nucleus is composed of rock, dust, and frozen gases, when heated by the Sun, the gases sublimate and produce an atmosphere surrounding the nucleus known as the coma. The force exerted on the coma by the Suns radiation pressure and solar wind cause an enormous tail to form, a typical comet nucleus has an albedo of 0.04. This is blacker than coal, and may be caused by a covering of dust, comets, or their precursors, formed in the outer Solar System, possibly millions of years before planet formation. How and when formed is debated, with distinct implications for Solar System formation, dynamics. Three-dimensional computer simulations indicate the structural features observed on cometary nuclei can be explained by pairwise low velocity accretion of weak cometesimals. The currently favored creation mechanism is that of the nebular hypothesis, astronomers think that comets originate in both the Oort cloud and the scattered disk. Most cometary nuclei are thought to be no more than about 10 miles across, the largest comets that have come inside the orbit of Saturn are C/2002 VQ94, Hale–Bopp, 29P, 109P/Swift–Tuttle, and 28P/Neujmin. The potato-shaped nucleus of Halleys comet contains equal amounts of ice, during a flyby in September 2001, the Deep Space 1 spacecraft observed the nucleus of Comet Borrelly and found it to be about half the size of the nucleus of Halleys Comet. Borrellys nucleus was also potato-shaped and had a black surface. Like Halleys Comet, Comet Borrelly only released gas from small areas where holes in the crust exposed the ice to sunlight, the nucleus of comet Hale–Bopp was estimated to be 60 ±20 km in diameter. Hale-Bopp appeared bright to the eye because its unusually large nucleus gave off a great deal of dust. The nucleus of P/2007 R5 is probably only 100–200 meters in diameter, the largest centaurs are estimated to be 250 km to 300 km in diameter. Three of the largest would include 10199 Chariklo,2060 Chiron, known comets have been estimated to have an average density of 0.6 g/cm3. Below is a list of comets that have had estimated sizes, densities, about 80% of the Halleys Comet nucleus is water ice, and frozen carbon monoxide makes up another 15%. Much of the remainder is carbon dioxide, methane. Scientists think that comets are chemically similar to Halleys Comet. The nucleus of Halleys Comet is also a dark black
6.
5D/Brorsen
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5D/Brorsen was a periodic Jupiter-family comet discovered February 26,1846, by the Danish astronomer Theodor Brorsen. The perihelion of 5D/Brorsen was February 25, just a day before its discovery, as a result of this close encounter to Earth the comets coma diameter increased. Johann Friedrich Julius Schmidt estimating it as 3 to 4 arcmin across on March 9, last seen on April 22, it was stationed about 20 degrees from the north celestial pole. By the end of this first apparition the orbital period was identified as 5.5 years and it was discovered that a close approach to Jupiter in 1842 put in its discovery orbit. The comets 5.5 year period would mean that apparitions would alternate between good and poor, as expected, the comet was missed in its 1851 apparition, when the comet only came as close as 1.5 AU to Earth. The comets orbit was still uncertain, made worse by the fact it had approached Jupiter in 1854. In 1857, Karl Christian Bruhns found a comet on 18 March 1857, soon an orbit was computed and it was found to be 5D/Brorsen, although predictions were three months off. The comet was followed until June 1857, and the orbit was now well known, the comet was missed in 1862, and the next recovery was in 1868. A close approach to Jupiter shortened the period enough to make the visible in 1873. A very favorable apparition followed in 1879, allowing the comet to be observed for the longest time to date – four months, the comet was missed in 1884, due to observing circumstances, but was also missed in 1890, a favorable apparition. The next favorable apparition occurred in 1901, but searches did not locate the comet, the next serious search was started by Brian G. Marsden, who believed the comet had faded out of existence, but computed the orbit for a very favorable 1973 apparition. Japanese observers made intensive searches for the comet, but nothing turned up, the comet is currently considered lost. ^ Orbital data taken from this preprint, Neslusan, Lubos, The identification of asteroid 1996 SK with the nucleus of comet 5D/Brorsen, Memorie della Società Astronomica Italiana. Conf. held at Palermo, Italy, June 11–16,2001 5D at Gary W. Kronks Cometography
7.
Perturbation (astronomy)
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In astronomy, perturbation is the complex motion of a massive body subject to forces other than the gravitational attraction of a single other massive body. The other forces can include a body, resistance, as from an atmosphere. The study of perturbations began with the first attempts to predict planetary motions in the sky, in ancient times the causes were a mystery. Newton, at the time he formulated his laws of motion and of gravitation, applied them to the first analysis of perturbations, the complex motions of gravitational perturbations can be broken down. The hypothetical motion that the body follows under the effect of one other body only is typically a conic section. This is called a problem, or an unperturbed Keplerian orbit. The differences between that and the motion of the body are perturbations due to the additional gravitational effects of the remaining body or bodies. If there is one other significant body then the perturbed motion is a three-body problem. A general analytical solution exists for the problem, when more than two bodies are considered analytic solutions exist only for special cases. Even the two-body problem becomes insoluble if one of the bodies is irregular in shape, most systems that involve multiple gravitational attractions present one primary body which is dominant in its effects. The gravitational effects of the bodies can be treated as perturbations of the hypothetical unperturbed motion of the planet or satellite around its primary body. In methods of general perturbations, general differential equations, either of motion or of change in the elements, are solved analytically, usually by series expansions. The result is expressed in terms of algebraic and trigonometric functions of the orbital elements of the body in question. This can be applied generally to many different sets of conditions, historically, general perturbations were investigated first. The classical methods are known as variation of the elements, variation of parameters or variation of the constants of integration, in these methods, it is considered that the body is always moving in a conic section, however the conic section is constantly changing due to the perturbations. General perturbations is applicable if the perturbing forces are about one order of magnitude smaller, or less. In the Solar System, this is usually the case, Jupiter, general perturbation methods are preferred for some types of problems, as the source of certain observed motions are readily found. In effect, the positions and velocities are perturbed directly, special perturbations can be applied to any problem in celestial mechanics, as it is not limited to cases where the perturbing forces are small
8.
Jupiter
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Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a giant planet with a mass one-thousandth that of the Sun, Jupiter and Saturn are gas giants, the other two giant planets, Uranus and Neptune are ice giants. Jupiter has been known to astronomers since antiquity, the Romans named it after their god Jupiter. Jupiter is primarily composed of hydrogen with a quarter of its mass being helium and it may also have a rocky core of heavier elements, but like the other giant planets, Jupiter lacks a well-defined solid surface. Because of its rotation, the planets shape is that of an oblate spheroid. The outer atmosphere is visibly segregated into several bands at different latitudes, resulting in turbulence, a prominent result is the Great Red Spot, a giant storm that is known to have existed since at least the 17th century when it was first seen by telescope. Surrounding Jupiter is a faint planetary ring system and a powerful magnetosphere, Jupiter has at least 67 moons, including the four large Galilean moons discovered by Galileo Galilei in 1610. Ganymede, the largest of these, has a greater than that of the planet Mercury. Jupiter has been explored on several occasions by robotic spacecraft, most notably during the early Pioneer and Voyager flyby missions and later by the Galileo orbiter. In late February 2007, Jupiter was visited by the New Horizons probe, the latest probe to visit the planet is Juno, which entered into orbit around Jupiter on July 4,2016. Future targets for exploration in the Jupiter system include the probable ice-covered liquid ocean of its moon Europa, Earth and its neighbor planets may have formed from fragments of planets after collisions with Jupiter destroyed those super-Earths near the Sun. Astronomers have discovered nearly 500 planetary systems with multiple planets, Jupiter moving out of the inner Solar System would have allowed the formation of inner planets, including Earth. Jupiter is composed primarily of gaseous and liquid matter and it is the largest of the four giant planets in the Solar System and hence its largest planet. It has a diameter of 142,984 km at its equator, the average density of Jupiter,1.326 g/cm3, is the second highest of the giant planets, but lower than those of the four terrestrial planets. Jupiters upper atmosphere is about 88–92% hydrogen and 8–12% helium by percent volume of gas molecules, a helium atom has about four times as much mass as a hydrogen atom, so the composition changes when described as the proportion of mass contributed by different atoms. Thus, Jupiters atmosphere is approximately 75% hydrogen and 24% helium by mass, the atmosphere contains trace amounts of methane, water vapor, ammonia, and silicon-based compounds. There are also traces of carbon, ethane, hydrogen sulfide, neon, oxygen, phosphine, the outermost layer of the atmosphere contains crystals of frozen ammonia. The interior contains denser materials - by mass it is roughly 71% hydrogen, 24% helium, through infrared and ultraviolet measurements, trace amounts of benzene and other hydrocarbons have also been found
9.
Solar System
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The Solar System is the gravitationally bound system comprising the Sun and the objects that orbit it, either directly or indirectly. Of those objects that orbit the Sun directly, the largest eight are the planets, with the remainder being significantly smaller objects, such as dwarf planets, of the objects that orbit the Sun indirectly, the moons, two are larger than the smallest planet, Mercury. The Solar System formed 4.6 billion years ago from the collapse of a giant interstellar molecular cloud. The vast majority of the mass is in the Sun. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being composed of rock. The four outer planets are giant planets, being more massive than the terrestrials. All planets have almost circular orbits that lie within a flat disc called the ecliptic. The Solar System also contains smaller objects, the asteroid belt, which lies between the orbits of Mars and Jupiter, mostly contains objects composed, like the terrestrial planets, of rock and metal. Beyond Neptunes orbit lie the Kuiper belt and scattered disc, which are populations of trans-Neptunian objects composed mostly of ices, within these populations are several dozen to possibly tens of thousands of objects large enough that they have been rounded by their own gravity. Such objects are categorized as dwarf planets, identified dwarf planets include the asteroid Ceres and the trans-Neptunian objects Pluto and Eris. In addition to two regions, various other small-body populations, including comets, centaurs and interplanetary dust clouds. Six of the planets, at least four of the dwarf planets, each of the outer planets is encircled by planetary rings of dust and other small objects. The solar wind, a stream of charged particles flowing outwards from the Sun, the heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of the interstellar medium, it extends out to the edge of the scattered disc. The Oort cloud, which is thought to be the source for long-period comets, the Solar System is located in the Orion Arm,26,000 light-years from the center of the Milky Way. For most of history, humanity did not recognize or understand the concept of the Solar System, the invention of the telescope led to the discovery of further planets and moons. The principal component of the Solar System is the Sun, a G2 main-sequence star that contains 99. 86% of the known mass. The Suns four largest orbiting bodies, the giant planets, account for 99% of the mass, with Jupiter. The remaining objects of the Solar System together comprise less than 0. 002% of the Solar Systems total mass, most large objects in orbit around the Sun lie near the plane of Earths orbit, known as the ecliptic
10.
Lexell's Comet
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D/1770 L1, popularly known as Lexells Comet after its orbit computer Anders Johan Lexell, was a comet discovered by astronomer Charles Messier in June 1770. It is notable for having passed closer to Earth than any comet in recorded history. The comet has not been seen since 1770 and is considered a lost comet, the comet was discovered on June 14,1770, in the constellation Sagittarius by Messier, who had just completed an observation of Jupiter and was examining several nebulae. The comet was also noted by other astronomers. The comet was observed in Japan, surviving records identify it as an astronomical and historical phenomenon. It was observed in the Hejaz in Safar 1184 AH, where some believed it to be the predicted by the poet al-Fasi. On July 1,1770, the comet passed 0.015 astronomical units from Earth, Charles Messier measured the coma as 2°23 across, around four times the apparent angular size of the Moon. Messier was the last astronomer to observe the comet as it moved away from the Sun, when it turned out that the parabolic solution was not a good fit to the comets orbit, Anders Johan Lexell suggested that the comet followed an elliptical orbit. His calculations, made over a period of years, gave a perihelion of August 13–14. It is, therefore, the earliest identified Jupiter family comet, the comet was never seen again. The comet likely no longer approaches any closer to the Sun than Jupiters orbit, although Comet Lexell was never seen again, it remained interesting to astronomers. The Paris Academy of Sciences offered a prize for an investigation into the orbit of the comet, johann Karl Burckhardt won in 1801, and confirmed the calculations of Lexell. He calculated that the 1779 close approach to Jupiter drastically altered its orbit and this foreshadowed the modern scientific idea of chaos. Lexells work on the orbit of the comet is considered to be the beginning of understanding of orbit determination. Tanuma Okitsugu, 1719–1788, Forerunner of Modern Japan, OCLC445621 D/1770 L1 Orbit Diagram, NASA JPL
11.
Extinct comet
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Extinct comets are comets that have expelled most of their volatile ice and have little left to form a tail or coma. The volatile material contained in the comet nucleus evaporates away, comets may go through a transition phase as they come close to extinction. A comet may be dormant rather than extinct, if its volatile component is sealed beneath a surface layer. Extinct comets are those that have expelled most of their volatile ice and have left to form a tail or coma. Over time, most of the material contained in a comet nucleus evaporates away. Other related types of comet include transition comets, that are close to becoming extinct, comets such as C/2001 OG108 may represent the transition between extinct comets and typical Halley-type comets or long period comets. Minor planets of the group of damocloids have been studied as possible extinct cometary candidates due to the similarity of their orbital parameters with those of Halley-type comets, dormant comets are those within which volatiles may be sealed, but which have inactive surfaces. For example,14827 Hypnos may be the nucleus of a comet that is covered by a crust several centimeters thick that prevents any remaining volatiles from outgassing. The term dormant comet is also used to describe comets that may become active but are not actively outgassing, for example,60558 Echeclus has displayed a cometary coma and now also has the cometary designation 174P/Echeclus. After passing perihelion in early 2008, centaur 52872 Okyrhoe significantly brightened, when discovered, asteroids were seen as a class of objects distinct from comets, and there was no unified term for the two until small Solar System body was coined by the IAU in 2006. The main difference between an asteroid and a comet is that a comet shows a coma due to sublimation of near-surface ices by solar radiation, a few objects have ended up being dual-listed because they were first classified as minor planets but later showed evidence of cometary activity. Conversely, some comets are eventually depleted of their volatile ices. A further distinction is that typically have more eccentric orbits than most asteroids. Also, they are theorized to be common objects amongst the bodies orbiting close to the Sun. Roughly six percent of the asteroids are thought to be extinct nuclei of comets which no longer experience outgassing
12.
Asteroid
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Asteroids are minor planets, especially those of the inner Solar System. The larger ones have also been called planetoids and these terms have historically been applied to any astronomical object orbiting the Sun that did not show the disc of a planet and was not observed to have the characteristics of an active comet. As minor planets in the outer Solar System were discovered and found to have volatile-based surfaces that resemble those of comets, in this article, the term asteroid refers to the minor planets of the inner Solar System including those co-orbital with Jupiter. There are millions of asteroids, many thought to be the remnants of planetesimals. The large majority of known asteroids orbit in the belt between the orbits of Mars and Jupiter, or are co-orbital with Jupiter. However, other orbital families exist with significant populations, including the near-Earth objects, individual asteroids are classified by their characteristic spectra, with the majority falling into three main groups, C-type, M-type, and S-type. These were named after and are identified with carbon-rich, metallic. The size of asteroids varies greatly, some reaching as much as 1000 km across, asteroids are differentiated from comets and meteoroids. In the case of comets, the difference is one of composition, while asteroids are composed of mineral and rock, comets are composed of dust. In addition, asteroids formed closer to the sun, preventing the development of the aforementioned cometary ice, the difference between asteroids and meteoroids is mainly one of size, meteoroids have a diameter of less than one meter, whereas asteroids have a diameter of greater than one meter. Finally, meteoroids can be composed of either cometary or asteroidal materials, only one asteroid,4 Vesta, which has a relatively reflective surface, is normally visible to the naked eye, and this only in very dark skies when it is favorably positioned. Rarely, small asteroids passing close to Earth may be visible to the eye for a short time. As of March 2016, the Minor Planet Center had data on more than 1.3 million objects in the inner and outer Solar System, the United Nations declared June 30 as International Asteroid Day to educate the public about asteroids. The date of International Asteroid Day commemorates the anniversary of the Tunguska asteroid impact over Siberia, the first asteroid to be discovered, Ceres, was found in 1801 by Giuseppe Piazzi, and was originally considered to be a new planet. In the early half of the nineteenth century, the terms asteroid. Asteroid discovery methods have improved over the past two centuries. This task required that hand-drawn sky charts be prepared for all stars in the band down to an agreed-upon limit of faintness. On subsequent nights, the sky would be charted again and any moving object would, hopefully, the expected motion of the missing planet was about 30 seconds of arc per hour, readily discernible by observers
13.
Hubble Space Telescope
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The Hubble Space Telescope is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. Although not the first space telescope, Hubble is one of the largest and most versatile, with a 2. 4-meter mirror, Hubbles four main instruments observe in the near ultraviolet, visible, and near infrared spectra. Hubbles orbit outside the distortion of Earths atmosphere allows it to take extremely high-resolution images, Hubble has recorded some of the most detailed visible light images ever, allowing a deep view into space and time. Many Hubble observations have led to breakthroughs in astrophysics, such as determining the rate of expansion of the universe. The HST was built by the United States space agency NASA, the Space Telescope Science Institute selects Hubbles targets and processes the resulting data, while the Goddard Space Flight Center controls the spacecraft. Space telescopes were proposed as early as 1923, Hubble was funded in the 1970s, with a proposed launch in 1983, but the project was beset by technical delays, budget problems, and the Challenger disaster. When finally launched in 1990, Hubbles main mirror was found to have been ground incorrectly, the optics were corrected to their intended quality by a servicing mission in 1993. Hubble is the telescope designed to be serviced in space by astronauts. After launch by Space Shuttle Discovery in 1990, five subsequent Space Shuttle missions repaired, upgraded, the fifth mission was canceled on safety grounds following the Columbia disaster. However, after spirited public discussion, NASA administrator Mike Griffin approved the fifth servicing mission, the telescope is operating as of 2017, and could last until 2030–2040. Its scientific successor, the James Webb Space Telescope, is scheduled for launch in 2018, the history of the Hubble Space Telescope can be traced back as far as 1946, to the astronomer Lyman Spitzers paper Astronomical advantages of an extraterrestrial observatory. In it, he discussed the two advantages that a space-based observatory would have over ground-based telescopes. First, the resolution would be limited only by diffraction, rather than by the turbulence in the atmosphere. Second, a telescope could observe infrared and ultraviolet light. Spitzer devoted much of his career to pushing for the development of a space telescope, space-based astronomy had begun on a very small scale following World War II, as scientists made use of developments that had taken place in rocket technology. An orbiting solar telescope was launched in 1962 by the United Kingdom as part of the Ariel space program, oAO-1s battery failed after three days, terminating the mission. It was followed by OAO-2, which carried out observations of stars and galaxies from its launch in 1968 until 1972. The continuing success of the OAO program encouraged increasingly strong consensus within the community that the LST should be a major goal
14.
177P/Barnard
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Comet 177P/Barnard, also known as Barnard 2, is a periodic comet with an orbital period of 119 years. It fits the definition of a Halley-type comet with. The comet, also designated P/2006 M3, was discovered by Edward Emerson Barnard on June 24,1889, on July 19,2006, 177P came within 0.36 AU of the Earth. From late July through September 2006 it was brighter than expected at 8th magnitude in the constellations Hercules, of Barnards other two periodic comets, the first, D/1884 O1 was last seen on November 20,1884, and is thought to have disintegrated. The last, 206P/Barnard-Boattini marked the beginning of a new era in cometary astronomy and it was a lost comet after 1892, until accidentally rediscovered on October 7,2008, by Andrea Boattini. Orbital simulation from JPL / Ephemeris 177P/Barnard – Kazuo Kinoshita 177P at Gary W. Kronks Cometography
15.
Edward Emerson Barnard
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Edward Emerson Barnard was an American astronomer. He was commonly known as E. E. Barnard, and was recognized as an observational astronomer. He is best known for his discovery of the proper motion of Barnards Star in 1916. Barnard was born in Nashville, Tennessee, to Reuben Barnard and Elizabeth Jane Barnard and his father died three months before his birth, so he grew up in an impoverished family and did not receive much in the way of formal education. His first interest was in the field of photography, and he became an assistant at the age of nine. He later developed an interest in astronomy, in 1876 he purchased a 5-inch refractor telescope, and in 1881 he discovered his first comet, but failed to announce his discovery. He found his second later the same year and a third in 1882. While he was working at a photography studio he was married to the English-born woman Rhoda Calvert in 1881. In the 1880s, Hulbert Harrington Warner offered US$200 per discovery of a new comet, Edward discovered a total of five, and used the money to build a house for himself and his bride. With his name being brought to the attention of astronomers in Nashville. Barnard never graduated from the school, but he did receive the honorary degree Vanderbilt has ever awarded. In 1889 he observed the moon Iapetus pass behind Saturns rings, as he watched Iapetus pass through the space between Saturns innermost rings and the planet itself, he saw a shadow pass over the moon. Although he did not realise it at the time, he had discovered proof of the spokes of Saturn and these spokes were doubted at first, but confirmed by the spacecraft Voyager 1. In 1892 he made observations of a nova and was the first to notice the gaseous emissions, the same year he also discovered Amalthea, the fifth moon of Jupiter. He was the first to discover a new moon of Jupiter since Galileo Galilei in 1609 and this was the last satellite discovered by visual observation. In 1895 he joined the University of Chicago as professor of astronomy, there he was able to use the 40-inch telescope at Yerkes Observatory. Much of his work during this period was taking photographs of the Milky Way, together with Max Wolf, he discovered that certain dark regions of the galaxy were actually clouds of gas and dust that obscured the more distant stars in the background. From 1905, his niece Mary R. Calvert worked as his assistant, the faint Barnards Star is named for Edward Barnard after he discovered in 1916 that it had a very large proper motion, relative to other stars
16.
Astronomical unit
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The astronomical unit is a unit of length, roughly the distance from Earth to the Sun. However, that varies as Earth orbits the Sun, from a maximum to a minimum. Originally conceived as the average of Earths aphelion and perihelion, it is now defined as exactly 149597870700 metres, the astronomical unit is used primarily as a convenient yardstick for measuring distances within the Solar System or around other stars. However, it is also a component in the definition of another unit of astronomical length. A variety of symbols and abbreviations have been in use for the astronomical unit. In a 1976 resolution, the International Astronomical Union used the symbol A for the astronomical unit, in 2006, the International Bureau of Weights and Measures recommended ua as the symbol for the unit. In 2012, the IAU, noting that various symbols are presently in use for the astronomical unit, in the 2014 revision of the SI Brochure, the BIPM used the unit symbol au. In ISO 80000-3, the symbol of the unit is ua. Earths orbit around the Sun is an ellipse, the semi-major axis of this ellipse is defined to be half of the straight line segment that joins the aphelion and perihelion. The centre of the sun lies on this line segment. In addition, it mapped out exactly the largest straight-line distance that Earth traverses over the course of a year, knowing Earths shift and a stars shift enabled the stars distance to be calculated. But all measurements are subject to some degree of error or uncertainty, improvements in precision have always been a key to improving astronomical understanding. Improving measurements were continually checked and cross-checked by means of our understanding of the laws of celestial mechanics, the expected positions and distances of objects at an established time are calculated from these laws, and assembled into a collection of data called an ephemeris. NASAs Jet Propulsion Laboratory provides one of several ephemeris computation services, in 1976, in order to establish a yet more precise measure for the astronomical unit, the IAU formally adopted a new definition. Equivalently, by definition, one AU is the radius of an unperturbed circular Newtonian orbit about the sun of a particle having infinitesimal mass. As with all measurements, these rely on measuring the time taken for photons to be reflected from an object. However, for precision the calculations require adjustment for such as the motions of the probe. In addition, the measurement of the time itself must be translated to a scale that accounts for relativistic time dilation
17.
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
18.
Andromedids
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The Andromedids meteor shower is associated with Bielas Comet, the showers occurring as Earth passes through old streams left by the comets tail. The comet was observed to have broken up by 1846, further drift of the pieces by 1852 suggested the moment of breakup was in either 1842 or early 1843, the breakup led to particularly spectacular showers in subsequent cycles. In the early 19th century, before the break-up of comet 3D/Biela, the first known sighting of the Andromedids was December 6,1741, over St Petersburg, Russia. Further strong showers were witnessed in 1798,1825,1830,1838 and 1847, the Andromedids produced spectacular displays of several thousand meteors per hour in 1872 and 1885, as a result of Earth crossing the comets debris stream. Schmidt, observing from Athens, said that the 1872 shower consisted mainly of faint meteors with broad and smoke-like trains, in Burma, the 1885 shower was perceived as a fateful omen and was indeed followed swiftly by the collapse of the Konbaung dynasty and the conquest by Britain. In recent years, peak activity had been less than three meteors per hour, around November 9 to 14, Andromedid activity of November comes from the newest streams, while that of early December comes from the oldest. On December 4,2011, six Canadian radar stations detected 50 meteors in an hour, the activity was likely from the 1649 stream. On December 8,2013, Meteor specialist Peter Brown reported that the Canadian Meteor Orbit Radar had recorded an outburst from the Andromedid meteors in the past 24 hours. Scientists postulate a somewhat weaker return in 2018, but a yield of up to 200 meteors an hour in 2023, Canadian Meteor Orbit Radar data also detected a spike of 30 meteors per hour on November 27,2008. During the 2012 shower an inconspicuous maximum occurred on November 9, history of the Andromedids and of the Biela Comet The Mother of All Meteor Storms
19.
Meteor shower
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A meteor shower is a celestial event in which a number of meteors are observed to radiate, or originate, from one point in the night sky. These meteors are caused by streams of debris called meteoroids entering Earths atmosphere at extremely high speeds on parallel trajectories. Most meteors are smaller than a grain of sand, so almost all of them disintegrate, intense or unusual meteor showers are known as meteor outbursts and meteor storms, which may produce greater than 1000 meteors an hour. The Meteor Data Centre lists about 600 suspected meteor showers of which about 100 are well established, the first great storm in modern times was the Leonids of November 1833. American Denison Olmsted explained the event most accurately, after spending the last weeks of 1833 collecting information he presented his findings in January 1834 to the American Journal of Science and Arts, published in January–April 1834, and January 1836. Work continued, however, coming to understand the nature of showers though the occurrences of storms perplexed researchers. In the 1890s, Irish astronomer George Johnstone Stoney and British astronomer Arthur Matthew Weld Downing, were the first to attempt to calculate the position of the dust at Earths orbit. They studied the dust ejected in 1866 by comet 55P/Tempel-Tuttle in advance of the anticipated Leonid shower return of 1898 and 1899, Meteor storms were anticipated, but the final calculations showed that most of the dust would be far inside of Earths orbit. The same results were independently arrived at by Adolf Berberich of the Königliches Astronomisches Rechen Institut in Berlin, although the absence of meteor storms that season confirmed the calculations, the advance of much better computing tools was needed to arrive at reliable predictions. In 1981 Donald K. Yeomans of the Jet Propulsion Laboratory reviewed the history of showers for the Leonids. A graph from it was adapted and re-published in Sky and Telescope and it showed relative positions of the Earth and Tempel-Tuttle and marks where Earth encountered dense dust. In 1985, E. D. Kondrateva and E. A. Reznikov of Kazan State University first correctly identified the years when dust was released which was responsible for several past Leonid meteor storms, in 1995, Peter Jenniskens predicted the 1995 Alpha Monocerotids outburst from dust trails. In anticipation of the 1999 Leonid storm, Robert H. McNaught, David Asher, in 2006 Jenniskens has published predictions for future dust trail encounters covering the next 50 years. Jérémie Vaubaillon continues to update predictions based on each year for the Institut de Mécanique Céleste et de Calcul des Éphémérides. Because meteor shower particles are all traveling in parallel paths, and at the same velocity and this radiant point is caused by the effect of perspective, similar to parallel railroad tracks converging at a single vanishing point on the horizon when viewed from the middle of the tracks. Meteor showers are almost always named after the constellation from which the appear to originate. This fixed point slowly moves across the sky during the due to the Earth turning on its axis. The radiant also moves slightly from night to night against the stars due to the Earth moving in its orbit around the sun
20.
27P/Crommelin
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Comet Crommelin, also known as Comet Pons-Coggia-Winnecke-Forbes, is a periodic comet with an orbital period of almost 28 years. It fits the definition of a Halley-type comet with. It is named after the British astronomer Andrew C. D. Crommelin who calculated its orbit in 1930 and it is one of only four comets not named after their discoverer, the other three being Comets Halley, Encke, and Lexell. The first observation was by Jean-Louis Pons on February 23,1818, johann Franz Encke attempted to calculate the orbit but was left with very large errors. The next observation was on November 10,1873 by Jérôme E. Coggia, and again on November 11 by Friedrich A. T. Winnecke, weiss and Hind took up the calculations and tried to match it again with the 1818 appearance. A third discovery was by Alexander F. I. Forbes on November 19,1928 and it was Crommelin who eventually established the orbit and finally linked the 1818 and 1873 comets to it. On its latest return, 27P/Crommelin was recovered on May 12,2011 at apparent magnitude 18.7 and peaked at magnitude 10.7 at perihelion on August 3
21.
289P/Blanpain
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289P/Blanpain, formerly D/1819 W1 is a short-period comet that was discovered by Jean-Jacques Blanpain on November 28,1819. Blanpain described the comet as having a small and confused nucleus. Another independent discovery was made on December 5 of that year by J. L. Pons, the comet was officially established as periodic comet 289P in July 2013, after being rediscovered by the Pan-STARRS survey during an outburst event. Comet D/1819 W1 has been proposed as the source of the Phoenicid meteor stream. Analysis of the orbits of asteroid 2003 WY25 have supported this conjecture, the comet currently has an Earth-MOID of 0.015 AU. 289P/Blanpain – Seiichi Yoshida @ aerith. net Gary W
22.
122P/de Vico
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122P/de Vico is a periodic comet with an orbital period of 74 years. It fits the definition of a Halley-type comet with. It was discovered by Francesco de Vico in Rome on February 20,1846, on 3 December 2153 the comet will pass about 0.694 AU from Uranus. Daniel Kirkwood in 1884 noticed that the comet shares elements with comet 12P/Pons-Brooks and he suggested that 122P had calved off Pons-Brooks some centuries prior. Later he identified the two comets capture into their orbits with their shared aphelion close to Neptune 991 CE. Orbital simulation from JPL / Horizons Ephemeris 122P/de Vico – Kazuo Kinoshita
23.
20D/Westphal
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20D/Westphal was a periodic comet with an orbital period of 61 years. It fits the definition of a Halley-type comet with. It was originally discovered by the German astronomer J. G. Westphal on July 24,1852 and it was independently discovered by the American astronomer Christian Heinrich Friedrich Peters on August 9. The comet was last seen between September 27 and November 26,1913, first by Pablo T. Delavan and then others and it was predicted to return in 1976 but was never observed, and is now considered a lost comet. Orbital simulation from JPL / Horizons Ephemeris 20D/Westphal, Comet Orbit Home Page 20D at Kronks Cometography Orbital elements, Infrared Processing and Analysis Center
24.
Perseids
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The Perseids /ˈpərsiːɪdz/ are a prolific meteor shower associated with the comet Swift–Tuttle. The Perseids are so called because the point from which appear to come, called the radiant. The name derives in part from the word Perseides, a found in Greek mythology referring to the sons of Perseus. The stream of debris is called the Perseid cloud and stretches along the orbit of the comet Swift–Tuttle, the cloud consists of particles ejected by the comet as it travels on its 133-year orbit. Most of the particles have been part of the cloud for around a thousand years, however, there is also a relatively young filament of dust in the stream that was pulled off the comet in 1865, which can give an early mini-peak the day before the maximum shower. The shower is visible from each year, with the peak in activity between 9 and 14 August, depending on the particular location of the stream. During the peak, the rate of meteors reaches 60 or more per hour and they can be seen all across the sky, however, because of the shower’s radiant in the constellation of Perseus, the Perseids are primarily visible in the Northern Hemisphere. While many meteors arrive between dawn and noon, they are not visible due to daylight. Some can also be seen before midnight, often grazing the Earth’s atmosphere to produce long bright trails, most Perseids burn up in the atmosphere while at heights above 80 kilometres. Some Catholics refer to the Perseids as the tears of Saint Lawrence, suspended in the sky but returning to once a year on August 10. In 1835, Adolphe Quetelet identified the shower as emanating from the constellation Perseus, in 1866, after the perihelion passage of Swift-Tuttle in 1862, the Italian astronomer Giovanni Virginio Schiaparelli discovered the link between meteor showers and comets. The finding is contained in an exchange of letters with Angelo Secchi
25.
Leonids
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The Leonids are a prolific meteor shower associated with the comet Tempel–Tuttle. The Leonids get their name from the location of their radiant in the constellation Leo and their proper Greek name should be Leontids, but the word was initially constructed as a Greek/Latin hybrid and it has been used since. They peak in the month of November, Earth moves through the meteoroid stream of particles left from the passages of a comet. The stream comprises solid particles, known as meteoroids, ejected by the comet as its frozen gases evaporate under the heat of the Sun when it is close enough – typically closer than Jupiters orbit. The Leonids are a fast moving stream which encounter the path of Earth, larger Leonids which are about 10 mm across have a mass of half a gram and are known for generating bright meteors. An annual Leonid shower may deposit 12 or 13 tons of particles across the entire planet, the meteoroids left by the comet are organized in trails in orbits similar to though different from that of the comet. They are differentially disturbed by the planets, in particular Jupiter and to an extent by radiation pressure from the sun, the Poynting–Robertson effect. These trails of meteoroids cause meteor showers when Earth encounters them, old trails are spatially not dense and compose the meteor shower with a few meteors per minute. In the case of the Leonids, that tends to peak around November 18, but some are spread through several days on either side, conversely, young trails are spatially very dense and the cause of meteor outbursts when the Earth enters one. Meteor storms exceed 1000 meteors per hour, to be compared to the sporadic background, the Leonids are famous because their meteor showers, or storms, can be among the most spectacular. It was marked by several nations of Native Americans, the Cheyenne established a peace treaty, abolitionists like Harriet Tubman and Frederick Douglass as well as slave-owners took note and others. The journalism of the event tended to rise above the partisan debates of the time, abraham Lincoln commented on it years later. Near Independence, Missouri, in Clay County, a refugee Mormon community watched the meteor shower on the banks of the Missouri River after having driven from their homes by local settlers. Though it was noted in the midwest and eastern areas it was noted in the far west. Denison Olmsted explained the event most accurately, after spending the last weeks of 1833 collecting information, he presented his findings in January 1834 to the American Journal of Science and Arts, published in January–April 1834, and January 1836. Accounts of the 1866 repeat of the Leonids counted hundreds per minute/a few thousand per hr in Europe, the Leonids were again seen in 1867, when moonlight reduced the rates to 1000 per hour. Another strong appearance of the Leonids in 1868 reached an intensity of 1000 per hour in dark skies and it was in 1866–67 that information on Comet Tempel-Tuttle was gathered pointing it out as the source of the meteor shower. When the storms failed to return in 1899, it was thought that the dust had moved on
26.
Solar conjunction
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Solar conjunction occurs when a planet or other solar system object is on the opposite side of the sun from the Earth. From an Earth reference, the sun will pass between the Earth and the object, communication with any spacecraft in solar conjunction will be severely limited due to the suns interference on radio transmissions from the spacecraft. When in reference to Satellite Communications, solar conjunction occurs when the sun is directly in line with an orbiting Satellite and the terrestrial receiving station. There is also a risk that an antenna equipped with auto-tracking will begin following the suns movements instead of the satellite once they are no longer inline with each other. This is because the Sun acts as a large electromagnetic noise generator which creates a much stronger than the satellites tracking signal. In autonomous mode Curiosity suspends all movements and active science operations, the term can also refer to the passage of the line of sight to an interior planet being very close to the solar disk. If the planet passes directly in front of the sun, a solar transit occurs
27.
15P/Finlay
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Comet Finlay is a periodic comet in the solar system discovered by William Henry Finlay on September 26,1886. It came to perihelion on December 27,2014, at apparent magnitude 10. When the first parabolic orbit calculations were made in 1886, there was a similarity between this orbit and that of Francesco de Vicos lost periodic comet of 1844. Lewis Boss noted large discrepancies between the orbits and after further observations concluded that de Vicos comet could not be the same as Finlays, the magnitude of the comet declined after 1926, and it was not until 1953 that it has been observed on every return. During the 2015 perihelion passage the comet outburst on 16 December 2014 from magnitude 11 to magnitude 9 becoming bright enough to be seen in common binoculars with a 50 mm objective lens. On December 23,2014, 15P and Mars were only 1/6 of a degree apart in the sky after sunset, but by December 23,2014, the comet had dimmed considerably since the outburst. On 16 January 2015, the comet outburst to magnitude 8, the comet currently has an Earth-MOID of 0.01 AU. On October 25,2060, the comet will pass roughly 0.04 AU from the Earth
28.
Comet Holmes
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Comet Holmes is a periodic comet in the Solar System, discovered by the British amateur astronomer Edwin Holmes on November 6,1892. It also briefly became the largest object in the Solar System, Comet Holmes was discovered by Edwin Holmes on November 6,1892, while he was conducting regular observations of the Andromeda Galaxy. The comets discovery was confirmed by Edward Walter Maunder, William Henry Maw, independent discoveries were made by Thomas David Anderson on November 8 and by Mike Brown and by John Ewen Davidson on November 9. The first calculations of the orbit of 17P/Holmes were done independently by Heinrich Kreutz. Additional orbits eventually established the date as June 13 and the orbital period as 6.9 years. These calculations proved that the comet was not a return of Bielas Comet, the 1899 and 1906 appearances were observed, but the comet was lost after 1906 until it was recovered on July 16,1964, by Elizabeth Roemer. Aided by the predictions of Brian G. Marsden, the comet has been observed on every subsequent return. During its 2007 return, Holmes unexpectedly brightened from a magnitude of about 17 to about 2.8 in a period of only 42 hours and this represents a change of brightness by a factor of about half a million and is the largest known outburst by a comet. The outburst took place from October 23 to 24,2007, the first person reportedly to notice a change was J. A. Henríquez Santana on Tenerife in the Canary Islands, minutes later, Ramón Naves in Barcelona noticed the comet at magnitude 7.3. It became easily visible to the eye as a bright yellow star in Perseus. Although large telescopes had already shown fine-scale cometary details, naked-eye observers saw Holmes as merely star-like until October 26, after that date, 17P/Holmes began to appear more comet-like to naked-eye observers. Based on orbital computations and luminosity before the 2007 outburst, the nucleus was estimated at 3.4 km. Comet Holmes not only became brighter, but it also swelled in size as its coma expanded, in late October 2007 the comas apparent diameter increased from 3.3 arcminutes to over 13 arcminutes, about half the diameter of the Moon in the sky. At a distance of around 2 AU, this means that the diameter of the coma had swelled to over 1 million km. By comparison, the Moon is 380,000 km from Earth, therefore, during the 2007 outburst of Comet Holmes the coma was a sphere wider than the diameter of the Moons orbit around Earth. On 2007 November, the coma had dispersed to a larger than the Sun. The cause of the outburst is not definitely known, the huge cloud of gas and dust may have resulted from a collision with a meteoroid, or, more probably, from a build-up of gas inside the comets nucleus that eventually broke through the surface. Energy from the Sun – insolation – was stored in the dust cover, the comet remained visible in February 2008 though it had become a challenging target at about magnitude +5 in the constellation Perseus
29.
25D/Neujmin
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Comet 25D/Neujmin, otherwise known as Comet Neujmin 2, is a periodic comet in the solar system discovered by Grigory N. Neujmin on February 24,1916. It was confirmed by George van Biesbroeck and Frank Watson Dyson on March 1, a prediction by Andrew Crommelin for 1921 was considered unfavourable and no observations were made. The next prediction for 2 January 1927 took into account an unnamed object observed in 1920, consequently, this comet has remained a lost comet since 1927. 25D at Kronks Cometography 25D at Kazuo Kinoshitas Comets 25D at Seiichi Yoshidas Comet Catalog
