1.
Jean-Louis Pons
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Jean-Louis Pons was a French astronomer. Pons was born at Peyre, Hautes-Alpes, to a poor family, in 1789, he began working for the Marseille observatory as a caretaker, and gradually gained some experience in assisting the astronomers with observations. He learned to make himself, showing a remarkable ability to remember star fields. In his early career, the unassuming and trusting Pons was often the target of jokes perpetrated by more experienced astronomers. Franz Xaver von Zach once advised him to look for comets when sunspots were visible, Pons made his first comet discovery, jointly attributed to Charles Messier, on 11 July 1801. He appears to have used telescopes and lenses of his own design, his Grand Chercheur seems to have been an instrument with large aperture and short focal length, however, he was not an especially diligent recorder of his observations, and his notes were often extremely vague. In 1819, Pons became the director of the new observatory at Marlia near Lucca, around that time he accepted the opportunity to become Director of the Florence Observatory at the request of the Grand Duke of Tuscany. He discovered five comets, three of which, 7P/Pons–Winnecke, 12P/Pons–Brooks and 273P/Pons–Gambart, bear his name. One observed on 26 November 1818 was named Comet Encke after Johann Franz Encke, Pons also co-discovered the comet formerly known as Pons–Coggia–Winnecke–Forbes and today known as 27P/Crommelin after Andrew Crommelin, who calculated its orbit. Pons received the French Academy of Sciencess Lalande Prize in 1818 for his discovery of three comets in that year and he won it again in 1820 for further comet discoveries at Marlia and for an unmatched third time in 1827 for discovering another seven comets at the Florence observatory. By 1827, Ponss eyesight had begun to fail, and he retired from observing altogether shortly before his death, in his honour, a moon crater was named after him. This article incorporates text from a now in the public domain, Chisholm, Hugh, ed. Pons. Biographical info Archive of Museo Galileo
2.
William Robert Brooks
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William Robert Brooks was a British-born American astronomer, mainly noted as being one of the most prolific discoverers of new comets of all time, second only to Jean-Louis Pons. He was born in Maidstone, England, the son of a Baptist minister who emigrated to Marion, son of Rev. William and Caroline Brooks. Brooks developed his interest in astronomy during a voyage to Australia. Brooks had a knowledge of lens construction, and was able to design and make his own telescopes, taking a year to grind. After marrying Mary E. Smith in 1870, Brooks moved to Phelps where he discovered his first comet in 1881, in 1886 he discovered 3 new comets. Brooks success at comet discovery was noticed by businessman William Smith, who, wishing to attract Brooks to Geneva, New York, built a new observatory and a home for Brooks family. Brooks went on to become Director of the Smith Observatory at Hobart College, Geneva, New York and his observations at the Smith Observatory produced 16 new comets. He specialized in the discovery of comets, including periodic comets 12P/Pons-Brooks and 16P/Brooks and he also discovered the bright naked-eye comet C/1911 O1, and was a pioneer of astrophotography. Brooks was also appointed a Professor and Honorary Doctor of Science by Hobart College, Smith Observatory. org Website featuring the history and current status of the Smith Observatory in Geneva, NY
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Apsis
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An apsis is an extreme point in an objects orbit. The word comes via Latin from Greek and is cognate with apse, for elliptic orbits about a larger body, there are two apsides, named with the prefixes peri- and ap-, or apo- added to a reference to the thing being orbited. For a body orbiting the Sun, the point of least distance is the perihelion, the terms become periastron and apastron when discussing orbits around other stars. For any satellite of Earth including the Moon the point of least distance is the perigee, for objects in Lunar orbit, the point of least distance is the pericynthion and the greatest distance the apocynthion. For any orbits around a center of mass, there are the terms pericenter and apocenter, periapsis and apoapsis are equivalent alternatives. A straight line connecting the pericenter and apocenter is the line of apsides and this is the major axis of the ellipse, its greatest diameter. For a two-body system the center of mass of the lies on this line at one of the two foci of the ellipse. When one body is larger than the other it may be taken to be at this focus. Historically, in systems, apsides were measured from the center of the Earth. In orbital mechanics, the apsis technically refers to the distance measured between the centers of mass of the central and orbiting body. However, in the case of spacecraft, the family of terms are used to refer to the orbital altitude of the spacecraft from the surface of the central body. The arithmetic mean of the two limiting distances is the length of the axis a. The geometric mean of the two distances is the length of the semi-minor axis b, the geometric mean of the two limiting speeds is −2 ε = μ a which is the speed of a body in a circular orbit whose radius is a. The words pericenter and apocenter are often seen, although periapsis/apoapsis are preferred in technical usage, various related terms are used for other celestial objects. The -gee, -helion and -astron and -galacticon forms are used in the astronomical literature when referring to the Earth, Sun, stars. The suffix -jove is occasionally used for Jupiter, while -saturnium has very rarely used in the last 50 years for Saturn. The -gee form is used as a generic closest approach to planet term instead of specifically applying to the Earth. During the Apollo program, the terms pericynthion and apocynthion were used when referring to the Moon, regarding black holes, the term peri/apomelasma was used by physicist Geoffrey A. Landis in 1998 before peri/aponigricon appeared in the scientific literature in 2002
4.
Astronomical unit
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The astronomical unit is a unit of length, roughly the distance from Earth to the Sun. However, that varies as Earth orbits the Sun, from a maximum to a minimum. Originally conceived as the average of Earths aphelion and perihelion, it is now defined as exactly 149597870700 metres, the astronomical unit is used primarily as a convenient yardstick for measuring distances within the Solar System or around other stars. However, it is also a component in the definition of another unit of astronomical length. A variety of symbols and abbreviations have been in use for the astronomical unit. In a 1976 resolution, the International Astronomical Union used the symbol A for the astronomical unit, in 2006, the International Bureau of Weights and Measures recommended ua as the symbol for the unit. In 2012, the IAU, noting that various symbols are presently in use for the astronomical unit, in the 2014 revision of the SI Brochure, the BIPM used the unit symbol au. In ISO 80000-3, the symbol of the unit is ua. Earths orbit around the Sun is an ellipse, the semi-major axis of this ellipse is defined to be half of the straight line segment that joins the aphelion and perihelion. The centre of the sun lies on this line segment. In addition, it mapped out exactly the largest straight-line distance that Earth traverses over the course of a year, knowing Earths shift and a stars shift enabled the stars distance to be calculated. But all measurements are subject to some degree of error or uncertainty, improvements in precision have always been a key to improving astronomical understanding. Improving measurements were continually checked and cross-checked by means of our understanding of the laws of celestial mechanics, the expected positions and distances of objects at an established time are calculated from these laws, and assembled into a collection of data called an ephemeris. NASAs Jet Propulsion Laboratory provides one of several ephemeris computation services, in 1976, in order to establish a yet more precise measure for the astronomical unit, the IAU formally adopted a new definition. Equivalently, by definition, one AU is the radius of an unperturbed circular Newtonian orbit about the sun of a particle having infinitesimal mass. As with all measurements, these rely on measuring the time taken for photons to be reflected from an object. However, for precision the calculations require adjustment for such as the motions of the probe. In addition, the measurement of the time itself must be translated to a scale that accounts for relativistic time dilation
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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.
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
9.
Ayurbarwada Buyantu Khan
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Buyantu Khan, born Ayurbarwada, also known by the temple name Renzong (Emperor Renzong of Yuan, was the fourth emperor of the Yuan dynasty. Apart from Emperor of China, he is regarded as the eighth Great Khan of the Mongol Empire or Mongols and his name means blessed/good Khan in the Mongolian language. His name Ayurbarwada was from a Sanskrit compound Āyur-parvata, which means the mountain of longevity, Ayurbarwada was the first Yuan emperor who actively supported the adoption of confucian principles into the Mongolian administration system. The emperor, who was mentored by the Confucian academic Li Meng, succeeded peacefully to the throne, more importantly, Ayurbarwada reinstituted the civil service examination system for the Yuan dynasty. Ayurbarwada was the son of Darmabala and Dagi of the Khunggirat. He had been tutored by the Confucian scholar Li Meng, who affected his future political attitudes since his early teens. In 1305 Bulugan Khatun removed Ayurbarwada from the court and sent him to Honan as the prince of Huai-ning, however, his uncle Temür Khan died without an heir on February 2,1307, because his son Tachu had died a year earlier before him. The Darkhan Harghasun, the chancellor of the government who became aware of Bulugans plan, recalled Ayurbarwada. They successfully developed a strategy to imprison both Ananda and Bulugan, afterwards, Ayurbarwada welcomed his older brother Khayishan, who was still far away from Dadu, to succeed to the throne. After the latters coronation, Ayurbarwada was appointed the Crown Prince in June 1307, the brothers promised each other that their descendants would rule in succession. Ayurbarwada was made head of the top central administrative organs known as the Zhongshu Sheng under his brother and he was able to read and write Chinese and appreciate Chinese paintings and calligraphy in addition to his deep knowledge of Confucianism and Chinese history. Strongly influenced by Confucian political ethics, he was opposed to his brothers exploitative policies. Khayishans partisans had accused Li Meng of having advised Ayurbarwada to keep the throne for himself, Ayurbarwada spoke out in Li Mengs defence but accomplished nothing much in the end. His disagreement with his brothers high officials remained concealed until his own enthronement and he was saluted under the title of Buyantu in his accession kuriltai. These reversals of policies can be traced to Ayurbarwadas cultural and ideological orientation, strongly influenced by Confucian political ethics as he was, he was naturally opposed to the exploitative policies carried out by the Department of State Affairs under Khaishan. Ayurbarwada was highlighted for his reform based on Confucianism principle for the Yuan government. As soon as he ascended to the throne, he disbanded of the Department of State Affairs set up during Khayishans reign and he also abolished the Zhida paper notes and coins issued by the court of Khayishan, and restored the Zhongtong and Zhiyuan notes as the only official currency. The bureaucracy was trimmed to the 1293 level and new offices were reduced to the original status they had had in Kublais reign
10.
Epsilon Geminorum
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Epsilon Geminorum, also named Mebsuta, is a star in the constellation of Gemini and is located on the outstretched right leg of the twin Castor. The apparent visual magnitude of +3.06 makes it one of the stars in this constellation. The distance to this star can be determined using parallax measurements, yielding a value of 840 light-years. Because Epsilon Geminorum is located near the ecliptic it can be occulted by the Moon or a planet, just such an occultation took place on April 8,1976 by Mars, which allowed the oblateness of the planets outer atmosphere to be measured. Prior to that, the star was occulted by Mercury on June 10,1940, on September 3,2015, Epsilon Geminorum is expected to be occulted by the asteroid Iphigenia. ε Geminorum is the stars Bayer designation and it bore the traditional names Mebsuta, Melboula or Melucta. Mebsuta has its roots in ancient Arabic where it and the star Mekbuda were the paws of a lion, Mebsuta comes from a phrase referring to the outstretched paw. In 2016, the International Astronomical Union organized a Working Group on Star Names to catalog, the WGSNs first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN, which included Mebsuta for this star. In Chinese, 井宿, meaning Well, refers to an asterism consisting of ε Geminorum, μ Geminorum, ν Geminorum, γ Geminorum, ξ Geminorum,36 Geminorum, ζ Geminorum and λ Geminorum. Alternatively, it may be a star that has passed through the giant branch stage. The estimated mass of this star is over 19 times the mass of the Sun, since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified. Epsilon Geminorum is radiating around 8,500 times the luminosity of the Sun from its atmosphere at an effective temperature of 4,662 K. It is this temperature that gives it the yellow-hued glow of a G-type star, a surface magnetic field with a strength of –0.14 ±0.19 G has been detected on this star. This topologically complex field is most likely generated by a formed from the deep convection zone in the stars outer envelope. USS Melucta was a United States Navy Crater class cargo ship named after the star
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Gamma Geminorum
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Gamma Geminorum, also named Alhena, is the third-brightest star in the constellation of Gemini. It has an apparent visual magnitude of 1.9, making it visible to the naked eye even in urban regions. Based upon parallax measurements with the Hipparcos satellite, it is located at a distance of roughly 109 light-years from the Sun, Alhena is an evolving star that is exhausting the supply of hydrogen at its core and has entered the subgiant stage. The spectrum matches a stellar classification of A0 IV, compared to the Sun it has 2.8 times the mass and 3.3 times the radius. It is radiating around 123 times the luminosity of the Sun from its outer envelope at a temperature of 9,260 K. This gives it a white hue typical of an A-class star and this is a spectroscopic binary system with a period of 12.6 years in a highly eccentric Keplerian orbit. γ Geminorum is the stars Bayer designation, the traditional name Alhena is derived from the Arabic الهنعة Al Hanah, the brand, whilst the alternate name Almeisan is from the Arabic المیسان Al Maisan, the shining one. Al Hanʽah was the name of star association consisting of this star, along with Mu Geminorum, Nu Geminorum, Eta Geminorum and they also were associated in Al Nuḥātai, the dual form of Al Nuḥāt, a Camels Hump. In 2016, the International Astronomical Union organized a Working Group on Star Names to catalog, the WGSNs first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN, which included Alhena for this star. In Chinese, 井宿, meaning Well, refers to an asterism consisting of γ Geminorum, μ Geminorum, ν Geminorum, ξ Geminorum, ε Geminorum,36 Geminorum, ζ Geminorum and λ Geminorum. Consequently, γ Geminorum itself is known as 井宿三 Alhena was the name of a Dutch ship that many people from an Italian cruise liner. In addition, the American attack cargo ship USS Alhena was named after the star
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Gemini (constellation)
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Gemini is one of the constellations of the zodiac. It was one of the 48 constellations described by the 2nd century AD astronomer Ptolemy and its name is Latin for twins, and it is associated with the twins Castor and Pollux in Greek mythology. Gemini lies between Taurus to the west and Cancer to the east, with Auriga and Lynx to the north and Monoceros, the Sun resides in the astrological sign of Gemini from June 20 to July 20 each year. By mid August, Gemini will appear along the horizon in the morning sky prior to sunrise. The best time to observe Gemini at night is overhead during the months of January and February, by April and May, the constellation will be visible soon after sunset in the west. The easiest way to locate the constellation is to find its two brightest stars Castor and Pollux eastward from the familiar “V” shaped asterism of Taurus and the three stars of Orion’s belt. Another way is to draw a line from the Pleiades star cluster located in Taurus. In doing so, you are drawing a line that is relatively close to the ecliptic. The constellation contains 85 stars visible to observation on Earth without a telescope, the brightest star in Gemini is Pollux, and the second brightest is Castor. Castors Bayer designation as Alpha is attributable to a mistake by Johann Bayer, α Gem is a sextuple star system 52 light-years from Earth, which appears as a magnitude 1.6 blue-white star to the unaided eye. Two spectroscopic binaries are visible at magnitudes 1.9 and 3.0 with a period of 470 years. A wide-set red dwarf star is also a part of the system, β Gem is an orange-hued giant star of magnitude 1.2,34 light-years from Earth. Pollux has an extrasolar planet revolving around it, as do two other stars in Gemini, HD50554, and HD59686, γ Gem is a blue-white hued star of magnitude 1.9,105 light-years from earth. δ Gem is a binary star 59 light-years from Earth. The primary is a star of magnitude 3.5. The period is over 1000 years, it is divisible in amateur telescopes. ε Gem, a star, includes a primary yellow supergiant of magnitude 3.1,900 light-years from Earth. The optical companion, of magnitude 9.2, is visible in binoculars and small telescopes
13.
Right ascension
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Right ascension is the angular distance measured eastward along the celestial equator from the vernal equinox to the hour circle of the point in question. When combined with declination, these astronomical coordinates specify the direction of a point on the sphere in the equatorial coordinate system. Right ascension is the equivalent of terrestrial longitude. Both right ascension and longitude measure an angle from a direction on an equator. Right ascension is measured continuously in a circle from that equinox towards the east. Any units of measure could have been chosen for right ascension, but it is customarily measured in hours, minutes. Astronomers have chosen this unit to measure right ascension because they measure a stars location by timing its passage through the highest point in the sky as the Earth rotates. The highest point in the sky, called meridian, is the projection of a line onto the celestial sphere. A full circle, measured in units, contains 24 × 60 × 60 = 86 400s, or 24 × 60 = 1 440m. Because right ascensions are measured in hours, they can be used to time the positions of objects in the sky. For example, if a star with RA = 01h 30m 00s is on the meridian, sidereal hour angle, used in celestial navigation, is similar to right ascension, but increases westward rather than eastward. Usually measured in degrees, it is the complement of right ascension with respect to 24h and it is important not to confuse sidereal hour angle with the astronomical concept of hour angle, which measures angular distance of an object westward from the local meridian. The Earths axis rotates slowly westward about the poles of the ecliptic and this effect, known as precession, causes the coordinates of stationary celestial objects to change continuously, if rather slowly. Therefore, equatorial coordinates are inherently relative to the year of their observation, coordinates from different epochs must be mathematically rotated to match each other, or to match a standard epoch. The right ascension of Polaris is increasing quickly, the North Ecliptic Pole in Draco and the South Ecliptic Pole in Dorado are always at right ascension 18h and 6h respectively. The currently used standard epoch is J2000.0, which is January 1,2000 at 12,00 TT, the prefix J indicates that it is a Julian epoch. Prior to J2000.0, astronomers used the successive Besselian Epochs B1875.0, B1900.0, the concept of right ascension has been known at least as far back as Hipparchus who measured stars in equatorial coordinates in the 2nd century BC. But Hipparchus and his successors made their star catalogs in ecliptic coordinates, the easiest way to do that is to use an equatorial mount, which allows the telescope to be aligned with one of its two pivots parallel to the Earths axis
14.
Declination
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In astronomy, declination is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declinations angle is measured north or south of the celestial equator, the root of the word declination means a bending away or a bending down. It comes from the root as the words incline and recline. Declination in astronomy is comparable to geographic latitude, projected onto the celestial sphere, points north of the celestial equator have positive declinations, while those south have negative declinations. Any units of measure can be used for declination, but it is customarily measured in the degrees, minutes. Declinations with magnitudes greater than 90° do not occur, because the poles are the northernmost and southernmost points of the celestial sphere, the Earths axis rotates slowly westward about the poles of the ecliptic, completing one circuit in about 26,000 years. This effect, known as precession, causes the coordinates of stationary celestial objects to change continuously, therefore, equatorial coordinates are inherently relative to the year of their observation, and astronomers specify them with reference to a particular year, known as an epoch. Coordinates from different epochs must be rotated to match each other. The currently used standard epoch is J2000.0, which is January 1,2000 at 12,00 TT, the prefix J indicates that it is a Julian epoch. Prior to J2000.0, astronomers used the successive Besselian Epochs B1875.0, B1900.0, the declinations of Solar System objects change very rapidly compared to those of stars, due to orbital motion and close proximity. This similarly occurs in the Southern Hemisphere for objects with less than −90° − φ. An extreme example is the star which has a declination near to +90°. Circumpolar stars never dip below the horizon, conversely, there are other stars that never rise above the horizon, as seen from any given point on the Earths surface. Generally, if a star whose declination is δ is circumpolar for some observer, then a star whose declination is −δ never rises above the horizon, as seen by the same observer. Likewise, if a star is circumpolar for an observer at latitude φ, neglecting atmospheric refraction, declination is always 0° at east and west points of the horizon. At the north point, it is 90° − |φ|, and at the south point, from the poles, declination is uniform around the entire horizon, approximately 0°. Non-circumpolar stars are visible only during certain days or seasons of the year, the Suns declination varies with the seasons. As seen from arctic or antarctic latitudes, the Sun is circumpolar near the summer solstice, leading to the phenomenon of it being above the horizon at midnight
15.
Pisces (constellation)
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Pisces is a constellation of the zodiac. Its name is the Latin plural for fish and it lies between Aquarius to the west and Aries to the east. The ecliptic and the equator intersect within this constellation and in Virgo. The vernal equinox is currently located in Pisces, due south of ω Psc, van Maanens Star, at 12.36 magnitude, is located in this constellation, along with others, such as HD222410, at 7.45 magnitude. It has many clusters of stars and the associated nebulae. It was discovered by Pierre Méchain, a French astronomer, in 1780, NGC488 is an isolated face-on prototypical spiral galaxy. NGC520 is a pair of colliding galaxies located 90 million lightyears away, CL 0024+1654 is a massive galaxy cluster that lenses the galaxy behind it, creating arc-shaped images of the background galaxy. 3C31 is a galaxy and radio source in Perseus located at a distance of 237 million light-years from Earth. Its jets, caused by the black hole at its center. Pisces originates from some composition of the Babylonian constellations Šinunutu4 the great swallow in current western Pisces, in the first-millennium BC texts known as the Astronomical Diaries, part of the constellation was also called DU. NU. NU. Pisces is associated with Aphrodite and Eros, who escaped from the monster Typhon by leaping into the sea, in order not to lose each other, they tied themselves together with rope. The Romans adopted the Greek legend, with Venus and Cupid acting as the counterparts for Aphrodite, the knot of the rope is marked by Alpha Piscium, also called Al-Rischa. Linum Boreum, χ – ρ,94 – VX – η – π – ο – α Psc, linum Austrinum, α – ξ – ν – μ – ζ – ε – δ –41 –35 – ω Psc. Piscis Austrinus, ω – ι – θ –7 – β –5 – κ,9 – λ – TX Psc. However the proposal was largely neglected by other astronomers with the exception of Admiral Smyth, who mentioned it in his book The Bedford Catalogue, and it is now obsolete. The Fishes are also associated with the German legend of Antenteh, who owned just a tub and they offered him a wish, which he refused. However, his wife begged him to return to the fish and this wish was granted, but her desires were not satisfied. She then asked to be a queen and have a palace, but when she asked to become a goddess, the tub in the story is sometimes recognized as the Great Square of Pegasus
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Cetus
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Its name refers to Cetus, a sea monster in Greek mythology, although it is often called the whale today. Cetus is located in the region of the sky that contains other water-related constellations such as Aquarius, Pisces and this is all the more true of asteroids, since their orbits usually have a greater inclination to the ecliptic than the moon and planets. For example, the asteroid 4 Vesta was discovered in this constellation in 1807, as seen from Mars, the ecliptic passes into Cetus, with the sun appearing in Cetus for around six days shortly after the northern summer solstice. Marss orbit is tilted by 1. 85° with respect to Earths, Mira, designated Omicron Ceti, was the first variable star to be discovered and the prototype of its class. Over a period of 332 days it reaches an apparent magnitude of 3 - visible to the naked eye - and dips to a minimum magnitude of 10. Its seeming appearance and disappearance gave it its name, which means the amazing one. Mira pulsates with a size of 400 solar diameters and a maximum size of 500 solar diameters. 420 light-years from Earth, it was discovered by David Fabricius in 1596, α Ceti, traditionally called Menkar, is a red-hued giant star of magnitude 2.5,220 light-years from Earth. It is a double star, the secondary is 93 Ceti. β Ceti, also called Deneb Kaitos and Diphda, is the brightest star in Cetus and it is an orange-hued giant star of magnitude 2.0,96 light-years from Earth. The traditional name Deneb Kaitos means the whales tail, γ Ceti, Kaffaljidhma is a very close double star. The primary is a star of magnitude 3.5,82 light-years from Earth. Tau Ceti is noted for being the nearest Sun-like star at a distance of 11.9 light-years and it is a yellow-hued main-sequence star of magnitude 3.5. AA Ceti is a star system, the brightest member has a magnitude of 6.2. The primary and secondary are separated by 8.4 arcseconds at an angle of 304 degrees, the tertiary is not visible in telescopes. AA Ceti is a variable star, the tertiary star passes in front of the primary. UV Ceti is a binary variable star. 8.7 light-years from Earth, the system consists of two red dwarfs, one of the stars is a flare star, which are prone to sudden, random outbursts that last several minutes, these increase the pairs apparent brightness significantly - as high as magnitude 7
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Eridanus (constellation)
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Eridanus is a constellation in the southern hemisphere. It is represented as a river and it was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations. It is the sixth largest of the modern constellations, the same name was later taken as a Latin name for the real Po River and also for the name of a minor river in Athens. At its southern end is the magnitude 0.5 star Achernar,144 light-years from Earth, it is a blue-white hued main sequence star whose traditional name means the rivers end. Achernar is a very peculiar star because it is one of the flattest stars known, observations indicate that its radius is about 50% larger at the equator than at the poles. This distortion occurs because the star is spinning extremely rapidly, there are several other noteworthy stars in Eridanus, including some double stars. Beta Eridani, traditionally called Cursa, is a star of magnitude 2.8,89 light-years from Earth. Its place to the south of Orions foot gives it its name, theta Eridani, called Acamar, is a binary star with blue-white components, distinguishable in small amateur telescopes and 161 light-years from Earth. The primary is of magnitude 3.2 and the secondary is of magnitude 4.3,32 Eridani is a binary star 290 light-years from Earth. The primary is a star of magnitude 4.8. 32 Eridani is divisible in amateur telescopes. 39 Eridani is a binary star divisible in small amateur telescopes,206 light-years from Earth. The primary is a giant star of magnitude 4.9. 40 Eridani is a star system consisting of an orange main-sequence star, a white dwarf. The orange main-sequence star is the primary of magnitude 4.4, the red dwarf, of magnitude 11, orbits the white dwarf every 250 years. The 40 Eridani system is 16 light-years from Earth, P Eridani is a binary star with two orange components,27 light-years from Earth. The magnitude 5.8 primary and 5.9 secondary have a period of 500 years. Epsilon Eridani is a star with one extrasolar planet similar to Jupiter and it is an orange-hued main-sequence star of magnitude 3.7,10.5 light-years from Earth
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Alexis Bouvard
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Alexis Bouvard was a French astronomer. He is particularly noted for his observations of the irregularities in the motion of Uranus. Born in Contamines, Duchy of Savoy, Bouvards achievements included the discovery of eight comets, while the former two tables were eminently successful, the latter showed substantial discrepancies with subsequent observations. This led Bouvard to hypothesise the existence of an eighth planet responsible for the irregularities in Uranus orbit, the position of Neptune was subsequently calculated from Bouvards observations, independently, by John Couch Adams and Urbain Le Verrier after his death. Bouvard was eventually director of the Paris Observatory after starting there as a student astronomer in 1793, Bouvard is also a semi-rural residential suburb, while Port Bouvard is a major residential development in the same region. All three locations are located within the city of Mandurah on the southwest coast of Western Australia, Bouvard, Alexis, Encyclopaedia Britannica, Deluxe CDROM edition
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Johann Franz Encke
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Johann Franz Encke was a German astronomer. Among his activities, he worked on the calculation of the periods of comets and asteroids, measured the distance from the earth to the sun, Encke was born in Hamburg, where his father was the Pastor at the St. James Church, Hamburg. He was the youngest of eight children, and at the time his father died when he was four, thanks to the financial assistance of a teacher, he was able to be educated at the Gelehrtenschule des Johanneums. In 1814 he resumed his studies at the University but after Napoleons escape from Elba he returned to the military, having returned to Göttingen in 1816, he was at once appointed by Bernhardt von Lindenau as his assistant in the observatory of Seeberg near Gotha. That comet is now called 12P/Pons-Brooks, at this time, all the known comets had an orbital period of seventy years and more, with an aphelion far beyond the orbit of Uranus. The most famous comet of this family was Comet Halley with its period of seventy-six years. So the orbit of the discovered by Pons was a sensation, because his orbit was found to have a period of 3.3 years. Encke predicted its return for 1822, but this return was only from the southern hemisphere and was seen by Carl Ludwig Christian Rümker in Australia. The comet was identified with the one seen by Pierre Méchain in 1786. Encke sent his calculations as a note to Gauss, Olbers and his former mathematics professor published this note and Encke became famous as the discoverer of the short periodic comets. The first object of this family, the Encke comet, was named after him and so it is one of the few comets not named after the discoverer, later this comet was identified as the origin of the Taurids meteor showers. The importance of the return based on the calculation by Encke was rewarded by the Royal Astronomical Society in London by presenting their Gold Medal to him in 1824. In this year Encke married Amalie Becker, daughter of author, bookseller and publisher Rudolph Zacharias Becker and they had three sons and two daughters. In 1825 he was elected a Fellow of the Royal Society, eight masterly treatises on the comets movements were published by him in the Berliner Abhandlungen. From a fresh discussion of the transits of Venus in 1761 and 1769 he deduced a solar parallax of 8.57 arcsecond and this and the corresponding distance to the sun were long accepted as authoritative. His results were published in two tracts, entitled Die Entfernung der Sonne. Mostly on the recommendation of Bessel, Encke became director of the new observatory and secretary of the Academy of Sciences, within the following time Encke was involved in the discovery and orbital parameter determination of other short periodic comets and asteroids. In 1837, Encke described a variation in the brightness of the A Ring of Saturn
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Beta Ceti
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Beta Ceti, also named Diphda, is the brightest star in the constellation of Cetus. Although designated beta, it is brighter than the alpha star in the constellation. This orange giant is easy to identify due to its location in a dark section of the celestial sphere. Based on parallax measurements, it lies at a distance of 96.3 light-years from the Sun. Diphda has an apparent visual magnitude of 2.02, making it the brightest star in Cetus. The stellar classification of this star is K0 III, although some sources list a classification of G9.5 III indicating that it lies along the line separating G-type from K-type stars. The luminosity class of III means that it is a giant star that has consumed the hydrogen at its core, after passing through the red giant stage, it underwent the helium flash event and is generating energy through the thermonuclear fusion of helium at its core. Beta Ceti will remain in this mode for over 100 million years, the effective temperature of the stars outer envelope is about 4,797 K, giving it the characteristic orange hue of a K-type star.8 times the Suns mass. This star displays flaring activity that results in random outbursts that increase the luminosity of the star over intervals lasting several days and this is a much longer duration than for comparable solar flare activity on the Sun, which typically last for periods measured in hours. In 2005, a high rate of X-ray emission was detected with the XMM-Newton space observatory. It is emitting about 2,000 times the X-ray luminosity of the Sun, β Ceti is the stars Bayer designation. It bore the traditional names Diphda and Deneb Kaitos, Diphda is Arabic for frog, from the phrase ضفدع الثاني aḍ-ḍifdaʿ aṯ-ṯānī the second frog, Deneb Kaitos is from ألذنب ألقيتوس ألجنوب Al Dhanab al Ḳaiṭos al Janūbīyy southern tail of Cetus. In 2016, the International Astronomical Union organized a Working Group on Star Names to catalogue, USS Diphda was a U. S. Navy ship. Lists of stars in the constellation Cetus Beta Ceti, Giant Stars Corona Brightens with Age
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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
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Jet Propulsion Laboratory
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The Jet Propulsion Laboratory is a federally funded research and development center and NASA field center in La Cañada Flintridge, California and Pasadena, California, United States. The JPL is managed by the nearby California Institute of Technology for NASA, the laboratorys primary function is the construction and operation of planetary robotic spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASAs Deep Space Network and they are also responsible for managing the JPL Small-Body Database, and provides physical data and lists of publications for all known small Solar System bodies. The JPLs Space Flight Operations Facility and Twenty-Five-Foot Space Simulator are designated National Historic Landmarks, JPL traces its beginnings to 1936 in the Guggenheim Aeronautical Laboratory at the California Institute of Technology when the first set of rocket experiments were carried out in the Arroyo Seco. Malinas thesis advisor was engineer/aerodynamicist Theodore von Kármán, who arranged for U. S. Army financial support for this GALCIT Rocket Project in 1939. In 1941, Malina, Parsons, Forman, Martin Summerfield, in 1943, von Kármán, Malina, Parsons, and Forman established the Aerojet Corporation to manufacture JATO motors. The project took on the name Jet Propulsion Laboratory in November 1943, during JPLs Army years, the laboratory developed two deployed weapon systems, the MGM-5 Corporal and MGM-29 Sergeant intermediate range ballistic missiles. These missiles were the first US ballistic missiles developed at JPL and it also developed a number of other weapons system prototypes, such as the Loki anti-aircraft missile system, and the forerunner of the Aerobee sounding rocket. At various times, it carried out testing at the White Sands Proving Ground, Edwards Air Force Base. A lunar lander was developed in 1938-39 which influenced design of the Apollo Lunar Module in the 1960s. The team lost that proposal to Project Vanguard, and instead embarked on a project to demonstrate ablative re-entry technology using a Jupiter-C rocket. They carried out three successful flights in 1956 and 1957. Using a spare Juno I, the two organizations then launched the United States first satellite, Explorer 1, on February 1,1958, JPL was transferred to NASA in December 1958, becoming the agencys primary planetary spacecraft center. JPL engineers designed and operated Ranger and Surveyor missions to the Moon that prepared the way for Apollo, JPL also led the way in interplanetary exploration with the Mariner missions to Venus, Mars, and Mercury. In 1998, JPL opened the Near-Earth Object Program Office for NASA, as of 2013, it has found 95% of asteroids that are a kilometer or more in diameter that cross Earths orbit. JPL was early to employ women mathematicians, in the 1940s and 1950s, using mechanical calculators, women in an all-female computations group performed trajectory calculations. In 1961, JPL hired Dana Ulery as their first woman engineer to work alongside male engineers as part of the Ranger and Mariner mission tracking teams, when founded, JPLs site was a rocky flood-plain just outside the city limits of Pasadena. Almost all of the 177 acres of the U. S, the city of La Cañada Flintridge, California was incorporated in 1976, well after JPL attained international recognition with a Pasadena address
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Saturn
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Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with a radius about nine times that of Earth. Although it has only one-eighth the average density of Earth, with its larger volume Saturn is just over 95 times more massive, Saturn is named after the Roman god of agriculture, its astronomical symbol represents the gods sickle. Saturns interior is composed of a core of iron–nickel and rock. This core is surrounded by a layer of metallic hydrogen, an intermediate layer of liquid hydrogen and liquid helium. Saturn has a yellow hue due to ammonia crystals in its upper atmosphere. Saturns magnetic field strength is around one-twentieth of Jupiters, the outer atmosphere is generally bland and lacking in contrast, although long-lived features can appear. Wind speeds on Saturn can reach 1,800 km/h, higher than on Jupiter, sixty-two moons are known to orbit Saturn, of which fifty-three are officially named. This does not include the hundreds of moonlets comprising the rings, Saturn is a gas giant because it is predominantly composed of hydrogen and helium. It lacks a definite surface, though it may have a solid core, Saturns rotation causes it to have the shape of an oblate spheroid, that is, it is flattened at the poles and bulges at its equator. Its equatorial and polar radii differ by almost 10%,60,268 km versus 54,364 km, Jupiter, Uranus, and Neptune, the other giant planets in the Solar System, are also oblate but to a lesser extent. Saturn is the planet of the Solar System that is less dense than water—about 30% less. Although Saturns core is considerably denser than water, the specific density of the planet is 0.69 g/cm3 due to the atmosphere. Jupiter has 318 times the Earths mass, while Saturn is 95 times the mass of the Earth, together, Jupiter and Saturn hold 92% of the total planetary mass in the Solar System. On 8 January 2015, NASA reported determining the center of the planet Saturn, the temperature, pressure, and density inside Saturn all rise steadily toward the core, which causes hydrogen to transition into a metal in the deeper layers. Standard planetary models suggest that the interior of Saturn is similar to that of Jupiter, having a rocky core surrounded by hydrogen. This core is similar in composition to the Earth, but more dense, in 2004, they estimated that the core must be 9–22 times the mass of the Earth, which corresponds to a diameter of about 25,000 km. This is surrounded by a liquid metallic hydrogen layer, followed by a liquid layer of helium-saturated molecular hydrogen that gradually transitions to a gas with increasing altitude
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Gas giant
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A gas giant is a giant planet composed mainly of hydrogen and helium. Jupiter and Saturn are the gas giants of the Solar System, for this reason, Uranus and Neptune are now often classified in the separate category of ice giants. Jupiter and Saturn consist mostly of hydrogen and helium, with heavier elements making up between 3 and 13 percent of the mass and they are thought to consist of an outer layer of molecular hydrogen surrounding a layer of liquid metallic hydrogen, with probably a molten rocky core. The outermost portion of their hydrogen atmosphere is characterized by layers of visible clouds that are mostly composed of water. The layer of metallic hydrogen makes up the bulk of each planet, the gas giants cores are thought to consist of heavier elements at such high temperatures and pressures that their properties are poorly understood. The defining differences between a very low-mass brown dwarf and a gas giant are debated, one school of thought is based on formation, the other, on the physics of the interior. Part of the debate concerns whether brown dwarfs must, by definition, have experienced nuclear fusion at some point in their history, the term gas giant was coined in 1952 by the science fiction writer James Blish and was originally used to refer to all giant planets. Arguably it is something of a misnomer, because throughout most of the volume of all giant planets the pressure is so high that matter is not in gaseous form. Other than solids in the core and the layers of the atmosphere, all matter is above the critical point. In the outer Solar System, hydrogen and helium are referred to as gases, water, methane, and ammonia as ices, and silicates and metals as rock. Because Uranus and Neptune are primarily composed of, in this terminology, ices, not gas, they are referred to as ice giants. Jupiter and Saturn are both class I, hot Jupiters are class IV or V. A cold hydrogen-rich gas giant more massive than Jupiter but less than about 500 M⊕ will only be larger in volume than Jupiter. For masses above 500 M⊕, gravity will cause the planet to shrink, kelvin–Helmholtz heating can cause a gas giant to radiate more energy than it receives from its host star. Although the words gas and giant are often combined, hydrogen planets need not be as large as the gas giants from the Solar System. However, smaller gas planets and planets closer to their star will lose atmospheric mass more quickly via hydrodynamic escape than larger planets and planets farther out. The smallest known extrasolar planet that is likely a gas planet is Kepler-138d, a low-mass gas planet can still have a radius resembling that of a gas giant if it has the right temperature. List of gravitationally rounded objects of the Solar System List of planet types
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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
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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
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Neptune
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Neptune is the eighth and farthest known planet from the Sun in the Solar System. In the Solar System, it is the fourth-largest planet by diameter, the planet. Neptune is 17 times the mass of Earth and is more massive than its near-twin Uranus. Neptune orbits the Sun once every 164.8 years at a distance of 30.1 astronomical units. It is named after the Roman god of the sea and has the astronomical symbol ♆, Neptune is not visible to the unaided eye and is the only planet in the Solar System found by mathematical prediction rather than by empirical observation. Unexpected changes in the orbit of Uranus led Alexis Bouvard to deduce that its orbit was subject to perturbation by an unknown planet. Neptune was subsequently observed with a telescope on 23 September 1846 by Johann Galle within a degree of the predicted by Urbain Le Verrier. Its largest moon, Triton, was discovered shortly thereafter, though none of the remaining known 14 moons were located telescopically until the 20th century. The planets distance from Earth gives it a small apparent size. Neptune was visited by Voyager 2, when it flew by the planet on 25 August 1989, the advent of the Hubble Space Telescope and large ground-based telescopes with adaptive optics has recently allowed for additional detailed observations from afar. Neptunes composition can be compared and contrasted with the Solar Systems other giant planets, however, its interior, like that of Uranus, is primarily composed of ices and rock, which is why Uranus and Neptune are normally considered ice giants to emphasise this distinction. Traces of methane in the outermost regions in part account for the blue appearance. In contrast to the hazy, relatively featureless atmosphere of Uranus, Neptunes atmosphere has active, for example, at the time of the Voyager 2 flyby in 1989, the planets southern hemisphere had a Great Dark Spot comparable to the Great Red Spot on Jupiter. These weather patterns are driven by the strongest sustained winds of any planet in the Solar System, because of its great distance from the Sun, Neptunes outer atmosphere is one of the coldest places in the Solar System, with temperatures at its cloud tops approaching 55 K. Temperatures at the centre are approximately 5,400 K. Neptune has a faint and fragmented ring system. On both occasions, Galileo seems to have mistaken Neptune for a star when it appeared close—in conjunction—to Jupiter in the night sky, hence. At his first observation in December 1612, Neptune was almost stationary in the sky because it had just turned retrograde that day and this apparent backward motion is created when Earths orbit takes it past an outer planet. Because Neptune was only beginning its yearly cycle, the motion of the planet was far too slight to be detected with Galileos small telescope
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Zacatecas
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Zacatecas, officially the Free and Sovereign State of Zacatecas, is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided in 58 municipalities and its capital city is Zacatecas City, Zacatecas is located in North-Central Mexico. The state is best known for its deposits of silver and other minerals, its colonial architecture. Its main economic activities are mining, agriculture and tourism, Zacatecas is located in the center-north of Mexico, and covers an area of 75, 284km2, the tenth largest state in the country. It borders the states of Jalisco, Aguascalientes, San Luis Potosí, Coahuila and Durango and is divided into fifty eight municipalities and 4,882, towns, cities and other communities. The state has an altitude of 2230 meters above sea level. The state has three geographical regions, the Sierra Madre Occidental in the west, the Mexican Plateau. Most of it is in the Sierra Madre Occidental with highly rugged with peaks of over 2,500 meters above sea level, the mountains of the southeast and northeast are lower but there large valleys such as the Juchipila and Tlaltenango. Most of the territory has only small mesas and other areas of flat land, in the center of the state, there is a small mountain chain called the Sierra de Fresnillo, from which much of the state’s mineral wealth comes from. In the extreme northwest, there is another important mountain chain called the Sierra de Sombrerete, marked by a mountain called Sombreretillo, near this chain is another called the Sierra de Órganos. No major rivers run through the state and most of the run only during the rainy season. The state belongs to two basins, the south east of the state belongs to the Lerma River basin, which eventually empties in the Pacific Ocean. Rivers belonging to this include the San Pedro, Juchipila, Jerez. The other basin is smaller and endorheic, and does not empty into any ocean, the state has eighty dams with a total capacity of 595,337 million cubic meters. The largest of these are the Leobardo Reynoso in Fresnillo, Miguel Aleman in Tlaltenango, much of the state’s water is underground divided into twenty hydraulic zones. These are accesses with over 5,800 wells mostly for agricultural use, most of the territory has a cool, dry climate, although areas in the south have more moisture, with most rain falling between June and September. The driest and coldest areas are in the northeast, known as the Salado because of its saltwater lakes, 75% of the state is arid or semi arid. 14% is arable and 79% is apt for the grazing of livestock, the average annual temperature is 16C with most of the state being temperate
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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
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Tunguska event
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The Tunguska event was a large explosion that occurred near the Stony Tunguska River, in Yeniseysk Governorate, Russia, on the morning of 30 June 1908. The explosion over the sparsely populated Eastern Siberian Taiga flattened 2,000 km2 of forest yet caused no known human casualties, the explosion is generally attributed to the air burst of a meteoroid. The Tunguska event is the largest impact event on Earth in recorded history, studies have yielded different estimates of the meteoroids size, on the order of 60 to 190 metres, depending on whether the body was a comet or a denser asteroid. Since the 1908 event, there have been an estimated 1,000 scholarly papers published on the Tunguska explosion. In 2013, a team of researchers published results of micro-samples from a peat bog near the center of the affected area showing fragments that may be of meteoritic origin. An explosion of this magnitude would be capable of destroying a large metropolitan area and this event has helped to spark discussion of asteroid impact avoidance. About ten minutes later, there was a flash and a similar to artillery fire. Eyewitnesses closer to the explosion reported that the source of the sound moved from the east to the north of them, the sounds were accompanied by a shock wave that knocked people off their feet and broke windows hundreds of kilometres away. The majority of witnesses reported only the sounds and tremors, eyewitness accounts vary regarding the sequence and duration of the events. The explosion registered at seismic stations across Eurasia and it is estimated that, in some places, the resulting shock wave was equivalent to an earthquake measuring 5.0 on the Richter magnitude scale. It also produced fluctuations in atmospheric pressure strong enough to be detected in Great Britain, testimony of S. Semenov, as recorded by Leonid Kuliks expedition in 1930, At breakfast time I was sitting by the house at Vanavara Trading Post, facing north. I suddenly saw that directly to the north, over Onkouls Tunguska Road, the split in the sky grew larger, and the entire northern side was covered with fire. At that moment I became so hot that I couldnt bear it, as if my shirt was on fire, from the northern side, where the fire was, came strong heat. I wanted to tear off my shirt and throw it down, but then the sky shut closed, and a strong thump sounded, I lost my senses for a moment, but then my wife ran out and led me to the house. After that such noise came, as if rocks were falling or cannons were firing, the earth shook, and when I was on the ground, I pressed my head down, fearing rocks would smash it. When the sky opened up, hot wind raced between the houses, like from cannons, which left traces in the ground like pathways, later we saw that many windows were shattered, and in the barn a part of the iron lock snapped. Testimony of Chuchan of Shanyagir tribe, as recorded by I. M. Suslov in 1926, suddenly we both woke up at the same time. We heard whistling and felt strong wind, Chekaren said, Can you hear all those birds flying overhead
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Extinction event
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An extinction event is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a change in the diversity. It occurs when the rate of extinction increases with respect to the rate of speciation, Extinction occurs at an uneven rate. Based on the record, the background rate of extinctions on Earth is about two to five taxonomic families of marine animals every million years. Marine fossils are used to measure extinction rates because of their superior fossil record. The Great Oxygenation Event was probably the first major extinction event, since the Cambrian explosion five further major mass extinctions have significantly exceeded the background extinction rate. In addition to the five mass extinctions, there are numerous minor ones as well. Mass extinctions seem to be a mainly Phanerozoic phenomenon, with extinction rates low before large complex organisms arose, estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. These differences stem from the chosen for describing an extinction event as major. In a landmark paper published in 1982, Jack Sepkoski and David M. Raup identified five mass extinctions, the Big Five cannot be so clearly defined, but rather appear to represent the largest of a relatively smooth continuum of extinction events. Cretaceous–Paleogene extinction event,66 Ma at the Cretaceous -Paleogene transition interval, the event formerly called the Cretaceous-Tertiary or K–T extinction or K-T boundary is now officially named the Cretaceous–Paleogene extinction event. About 17% of all families, 50% of all genera and 75% of all species became extinct, in the seas all the ammonites, plesiosaurs and mosasaurs disappeared and the percentage of sessile animals was reduced to about 33%. All non-avian dinosaurs became extinct during that time, the boundary event was severe with a significant amount of variability in the rate of extinction between and among different clades. Mammals and birds, the latter descended from dinosaurs, emerged as dominant large land animals. Triassic–Jurassic extinction event,201.3 Ma at the Triassic-Jurassic transition, about 23% of all families, 48% of all genera and 70% to 75% of all species became extinct. Most non-dinosaurian archosaurs, most therapsids, and most of the amphibians were eliminated. Non-dinosaurian archosaurs continued to dominate aquatic environments, while non-archosaurian diapsids continued to dominate marine environments, the Temnospondyl lineage of large amphibians also survived until the Cretaceous in Australia. Permian–Triassic extinction event,252 Ma at the Permian-Triassic transition, Earths largest extinction killed 57% of all families, 83% of all genera and 90% to 96% of all species
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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
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Bird migration
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Bird migration is the regular seasonal movement, often north and south along a flyway, between breeding and wintering grounds. Migration carries high costs in predation and mortality, including from hunting by humans and it occurs mainly in the northern hemisphere, where birds are funnelled on to specific routes by natural barriers such as the Mediterranean Sea or the Caribbean Sea. More recently, Johannes Leche began recording dates of arrivals of spring migrants in Finland in 1749, threats to migratory birds have grown with habitat destruction especially of stopover and wintering sites, as well as structures such as power lines and wind farms. The Arctic tern holds the long-distance migration record for birds, travelling between Arctic breeding grounds and the Antarctic each year, shorter migrations are common, including altitudinal migrations on mountains such as the Andes and Himalayas. The timing of migration seems to be controlled primarily by changes in day length, migrating birds navigate using celestial cues from the sun and stars, the earths magnetic field, and probably also mental maps. Records of bird migration were made as much as 3,000 years ago by the Ancient Greek writers Hesiod, Homer, Herodotus and Aristotle. The Bible also notes migrations, as in the Book of Job, the author of Jeremiah wrote, Even the stork in the heavens knows its seasons, and the turtle dove, the swift and the crane keep the time of their arrival. Aristotle noted that cranes traveled from the steppes of Scythia to marshes at the headwaters of the Nile, pliny the Elder, in his Historia Naturalis, repeats Aristotles observations. Aristotle however suggested that swallows and other birds hibernated and this belief persisted as late as 1878, when Elliott Coues listed the titles of no less than 182 papers dealing with the hibernation of swallows. It was not until the end of the century that migration as an explanation for the winter disappearance of birds from northern climes was accepted. Bewick then describes an experiment which succeeded in keeping alive in Britain for several years. He concludes, These experiments have since been confirmed by. Migration is the seasonal movement, often north and south. Bird movements include those made in response to changes in food availability, habitat, sometimes, journeys are not termed true migration because they are irregular or in only one direction. Migration is marked by its annual seasonality, non-migratory birds are said to be resident or sedentary. Approximately 1800 of the worlds 10,000 bird species are long-distance migrants, many bird populations migrate long distances along a flyway. The most common pattern involves flying north in the spring to breed in the temperate or Arctic summer, of course, in the southern hemisphere the directions are reversed, but there is less land area in the far south to support long-distance migration. The primary motivation for migration appears to be food, for example, also, the longer days of the northern summer provide extended time for breeding birds to feed their young
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ArXiv
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In many fields of mathematics and physics, almost all scientific papers are self-archived on the arXiv repository. Begun on August 14,1991, arXiv. org passed the half-million article milestone on October 3,2008, by 2014 the submission rate had grown to more than 8,000 per month. The arXiv was made possible by the low-bandwidth TeX file format, around 1990, Joanne Cohn began emailing physics preprints to colleagues as TeX files, but the number of papers being sent soon filled mailboxes to capacity. Additional modes of access were added, FTP in 1991, Gopher in 1992. The term e-print was quickly adopted to describe the articles and its original domain name was xxx. lanl. gov. Due to LANLs lack of interest in the rapidly expanding technology, in 1999 Ginsparg changed institutions to Cornell University and it is now hosted principally by Cornell, with 8 mirrors around the world. Its existence was one of the factors that led to the current movement in scientific publishing known as open access. Mathematicians and scientists regularly upload their papers to arXiv. org for worldwide access, Ginsparg was awarded a MacArthur Fellowship in 2002 for his establishment of arXiv. The annual budget for arXiv is approximately $826,000 for 2013 to 2017, funded jointly by Cornell University Library, annual donations were envisaged to vary in size between $2,300 to $4,000, based on each institution’s usage. As of 14 January 2014,174 institutions have pledged support for the period 2013–2017 on this basis, in September 2011, Cornell University Library took overall administrative and financial responsibility for arXivs operation and development. Ginsparg was quoted in the Chronicle of Higher Education as saying it was supposed to be a three-hour tour, however, Ginsparg remains on the arXiv Scientific Advisory Board and on the arXiv Physics Advisory Committee. The lists of moderators for many sections of the arXiv are publicly available, additionally, an endorsement system was introduced in 2004 as part of an effort to ensure content that is relevant and of interest to current research in the specified disciplines. Under the system, for categories that use it, an author must be endorsed by an established arXiv author before being allowed to submit papers to those categories. Endorsers are not asked to review the paper for errors, new authors from recognized academic institutions generally receive automatic endorsement, which in practice means that they do not need to deal with the endorsement system at all. However, the endorsement system has attracted criticism for allegedly restricting scientific inquiry, perelman appears content to forgo the traditional peer-reviewed journal process, stating, If anybody is interested in my way of solving the problem, its all there – let them go and read about it. The arXiv generally re-classifies these works, e. g. in General mathematics, papers can be submitted in any of several formats, including LaTeX, and PDF printed from a word processor other than TeX or LaTeX. The submission is rejected by the software if generating the final PDF file fails, if any image file is too large. ArXiv now allows one to store and modify an incomplete submission, the time stamp on the article is set when the submission is finalized
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Coma (cometary)
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The coma is the nebulous envelope around the nucleus of a comet, formed when the comet passes close to the Sun on its highly elliptical orbit, as the comet warms, parts of it sublimes. This gives a comet a fuzzy appearance when viewed in telescopes and distinguishes it from stars, the word coma comes from the Greek kome, which means hair and is the origin of the word comet itself. The coma is generally made of ice and comet dust, water dominates up to 90% of the volatiles that outflow from the nucleus when the comet is within 3-4 AU of the Sun. The parent molecule is destroyed primarily through photodissociation and to a smaller extent photoionization. The solar wind plays a role in the destruction of water compared to photochemistry. Larger dust particles are left along the orbital path while smaller particles are pushed away from the Sun into the comets tail by light pressure. Comas typically grow in size as comets approach the Sun, and they can be as large as the diameter of Jupiter, about a month after an outburst in October 2007, comet 17P/Holmes briefly had a tenuous dust atmosphere larger than the Sun. The Great Comet of 1811 also had a coma roughly the diameter of the Sun, even though the coma can become quite large, its size can actually decrease about the time it crosses the orbit of Mars around 1.5 AU from the Sun. At this distance the solar wind becomes strong enough to blow the gas and dust away from the coma, Comets were found to emit X-rays in late-March 1996. This surprised researchers, because X-ray emission is associated with very high-temperature bodies. This ripping off leads to the emission of X-rays and far ultraviolet photons, with basic Earth-surface based telescope and some technique, the size of the Coma can be calculated. Called the drift method, one locks the telescope in position and that time multiplied by the cosine of comets declination, times.25 should equal the comas diameter in arcminutes. If the distance to the comet is known, then the apparent size of the coma can be determined. In 2015, it was noted that the ALICE instrument on the ESA Rosetta spacecraft to comet 67/P, detected hydrogen, oxygen, carbon and nitrogen in the Coma, which they also called the Comets atmosphere. Alice is a spectrograph, and it found that electrons created by UV light were colliding and breaking up molecules of water. OAO-2 discovered large halos of hydrogen gas around comets, space probe Giotto detected hydrogen ions at distance of 7.8 million km away from Halley when it did close flyby of the comet in 1986. A hydrogen gas halo was detected to be 15 times the diameter of Sun and this triggered NASA to point the Pioneer Venus mission at the Comet, and it was determined that the Comet emitting 12 tons of water per second. The hydrogen gas emission has not been detected from Earths surface because those wavelengths are blocked by the atmosphere, the process by which water is broken down into hydrogen and oxygen was studied by the ALICE instrument aboard the Rosetta spacecraft
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Comet tail
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A comet tail—and coma—are features visible in comets when they are illuminated by the Sun and may become visible from Earth when a comet passes through the inner Solar System. As a comet approaches the inner Solar System, solar radiation causes the materials within the comet to vaporize and stream out of the nucleus. Separate tails are formed of dust and gases, becoming visible through different phenomena, the dust reflects sunlight directly, most comets are too faint to be visible without the aid of a telescope, but a few each decade become bright enough to be visible to the naked eye. In the outer Solar System, comets remain frozen and are difficult or impossible to detect from Earth due to their small size. As a comet approaches the inner Solar System, solar radiation causes the materials within the comet to vaporize and stream out of the nucleus. The streams of dust and gas each form their own distinct tail, the tail of dust is left behind in the comets orbit in such a manner that it often forms a curved tail called the antitail, only when it seems that it is directed towards the Sun. At the same time, the ion tail, made of gases, the ion tail follows the magnetic field lines rather than an orbital trajectory. Parallax viewing from the Earth may sometimes mean the tails appear to point in opposite directions. While the solid nucleus of comets is generally less than 50 km across, the coma may be larger than the Sun, the Ulysses spacecraft made an unexpected pass through the tail of the comet C/2006 P1, on February 3,2007. Evidence of the encounter was published in the October 1,2007 issue of the Astrophysical Journal, the observation of antitails contributed significantly to the discovery of solar wind. The ion tail is the result of ultraviolet radiation ejecting electrons off particles in the coma, once the particles have been ionised, they form a plasma which in turn induces a magnetosphere around the comet. The comet and its magnetic field form an obstacle to outward flowing solar wind particles. The comet is supersonic relative to the wind, so a bow shock is formed upstream of the comet. In this bow shock, large concentrations of cometary ions congregate, the field lines drape around the comet forming the ion tail. If the ion tail loading is sufficient, then the field lines are squeezed together to the point where, at some distance along the ion tail. This leads to a disconnection event. This has been observed on a number of occasions, notable among which was on the 20th, april 2007 when the ion tail of comet Encke was completely severed as the comet passed through a coronal mass ejection. This event was observed by the STEREO spacecraft, a disconnection event was also seen with C/2009 R1 on May 26,2010
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Antitail
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An antitail is a spike projecting from a comets coma which seems to go towards the Sun, and thus geometrically opposite to the other tails, the ion tail and the dust tail. However, this phenomenon is an illusion that is seen from the Earth. As Earth passes through the orbital plane, this disc is seen side on. The other side of the disc can sometimes be seen, though it tends to be lost in the dust tail, the antitail is therefore normally visible for a brief interval only when Earth passes through the comets orbital plane. Comet tail The coma and tail at the main Comet article, image of Comet Arend-Roland with prominent antitail Emily Lakdawalla. Spot a comet near Saturn tonight, online Encyclopedia of Science - Antitail
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Comet dust
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Comet dust refers to cosmic dust that originates from a comet. Comet dust can provide clues to comets origin, when the Earth passes through a comet dust trail, it can produce a meteor shower. Bulk properties of the comet dust such as density as well as the composition can distinguish between the models. For example, the ratios of comet and of interstellar dust are very similar. The 1) interstellar model says that ices formed on dust grains in the cloud that preceded the Sun. The mix of ice and dust then aggregated into a comet without appreciable chemical modification, J. Mayo Greenberg first proposed this idea in 1986. In the 2) Solar System model, the ices that formed in the interstellar cloud first vaporized as part of the disk of gas. The vaporized ices later resolidified and assembled into comets, so the comets in this model would have a different composition than those comets that were made directly from interstellar ice. The 3) primordial rubble pile model for comet formation says that comets agglomerate in the region where Jupiter was forming, the composition of the dust of comet Wild 2 is similar to the composition of dust found in the outer regions of the accretion disks around newly-forming stars. A comet and its dust allow investigation of the Solar System beyond the main planetary orbits, comets are distinguished by their orbits, long period comets have long elliptical orbits, randomly inclined to the plane of the Solar System, and with periods greater than 200 years. A comet will experience a range of conditions as it traverses its orbit. For long period comets, most of the time it will be so far from the Sun that it will be too cold for evaporation of ices to occur, near the Sun, the heating and evaporation rate will be so great, that no dust can be retained. Therefore, the thickness of dust layers covering the nuclei of a comet can indicate how closely, if a comet has an accumulation of thick dust layers, it may have frequent perihelion passages that dont approach the Sun too closely. The accumulation of dust layers over time would change the character of the short-period comet. A dust layer both inhibits the heating of the cometary ices by the Sun, and slows the loss of gases from the nucleus below
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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
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Lost comet
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The D/ designation is for a periodic comet that no longer exists or is deemed to have disappeared. Some astronomers have specialized in this area, such as Brian G. Marsden, there are a number of reasons why a comet might be missed by astronomers during subsequent apparitions. Firstly, cometary orbits may be perturbed by interaction with the giant planets and this, along with nongravitational forces, can result in changes to the date of perihelion. As some comets periodically undergo outbursts or flares in brightness, it may be possible for a faint comet to be discovered during an outburst. Comets can also run out of volatiles and this may have occurred in the case of 5D/Brorsen, which was considered by Marsden to have probably faded out of existence in the late 19th century. Comets are in some known to have disintegrated during their perihelion passage. The best-known example is Bielas Comet, which was observed to split into two components before disappearing after its 1852 apparition, in modern times 73P/Schwassmann–Wachmann has been observed in the process of breaking up. In the case of lost comets this is especially tricky, for example, the comet 177P/Barnard, discovered by Edward Emerson Barnard on June 24,1889, was rediscovered after 116 years in 2006. On July 19,2006, 177P came within 0.36 AU of the Earth, comets can be gone but not considered lost, even though they may not be expected back for hundreds or even thousands of years. With more powerful telescopes it has become possible to observe comets for longer periods of time after perihelion, for example, Comet Hale–Bopp was observable with the naked eye about 18 months after its approach in 1997. It is expected to remain observable with large telescopes until perhaps 2020, comets that have been lost or which have disappeared have names beginning with a D according to current IAU conventions. Comets are typically observed on a periodic return, when they do not they are sometimes found again, while other times they may break up into fragments. These fragments can sometimes be observed, but the comet is no longer expected to return. Other times a comet will not be considered lost until it does not appear at a predicted time, comets may also collide with another object, such as Comet Shoemaker–Levy 9, which collided with Jupiter in 1994
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