1.
The Occultation
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Some Shiis, such as the Nizari Ismaili, do not believe in the idea of the Occultation. The groups that do believe in it differ on the succession of the Imamate, the Hidden Imam is still considered to be the Imam of the Time, to hold authority over the community, and to guide and protect individuals and the Shii community. In Twelver Shia Islam, the largest branch of the Shia faith, twelfth imam, Muhammad al-Mahdi, the Occultation is split into the Minor Occultation and the Major Occultation. According to Shia, there are reasons for the Occultation, Imam being afraid of his being killed, not to be under the oath of tyrant rulers, the Minor Occultation refers to the period when the Twelver Shia believe the Imam still maintained contact with his followers via deputies. During this period, from 874-941, the deputies represented him, Shia believe that in 873, after the death of his father al-Askari, the eleventh Imam, the 12th Imam was hidden from the authorities of the Abbasid caliphate as a precaution. His whereabouts were disclosed only to a select few, four close associates of his father became mediators known as Saf’ir, or between the Imam and his followers, until the year 941. This period is considered by Twelvers to be the first, or Minor Occultation, when believers faced difficulty, they would write their concerns and send them to his deputy. The deputy would receive the decision of the Imam, endorse it with his seal and signature, the deputies also collected zakat and khums on his behalf. For the Shia, the idea of consulting a hidden Imam was not something new, according to Twelvers, under the critical situation caused by Abbasides, Jaafar al-Sadiq was the first to base the underground system of communication in the Shia community. By the time of al-Javad, the agents took the tactic of al-Taqiyya to take part in government, from the time of al-Reza, the Imams were under the direct control of the authorities and the direct contact between the Imam and the community was disconnected. The situation led to the increase in the role of deputies, the deputies undertook the tasks of Imams to release them from the pressure of the Abbasids. The fourth deputy died six days later, and twelvers continue to await the reappearance of the Mahdi, in the same year, many notable Shia scholars such as Ali ibn Babwayh Qummi and Muhammad ibn Yaqub Kulayni, the learned compiler of al-Kafi also died. The Major Occultation denotes the second, longer portion of the Occultation, Shia believe, based on the last Saf’irs deathbed message, that the Twelfth Imam had decided not to appoint another deputy. Thus, al-Samarris death marked the beginning of the second or Major Occultation, according to the last letter of Muhammad al-Mahdi to Ali ibn Muhammad al-Samarri, from the day of your death the period of my major occultation will begin. Henceforth, no one will see me, unless and until Allah makes me appear and my reappearance will take place after a very long time when people will have grown tired of waiting and those who are weak in their faith will say, What. Rest assured, no one has a relationship with God. Whoever denies me is not from my, the appearance of the Relief depends solely upon God. Therefore, those who propose a certain time for it are liars, as to the benefit of my existence in occultation, it is like the benefit of the sun behind the clouds where the eyes do not see it
2.
Aldebaran
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Aldebaran, designated Alpha Tauri, is an orange giant star located about 65 light years from the Sun in the zodiac constellation of Taurus. It is the brightest star in its constellation and usually the fourteenth-brightest star in the nighttime sky and it is likely that Aldebaran hosts a planet several times the size of Jupiter. The planetary exploration probe Pioneer 10 is currently heading in the direction of the star. Alpha Tauri is the stars Bayer designation, the name Aldebaran is Arabic and means the Follower, presumably because it rises near and soon after the Pleiades. 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 Aldebaran for this star. It is now so entered in the IAU Catalog of Star Names, in Persia it was known as Tascheter. In the Middle Ages it was sometimes called Cor Tauri, john Gower refers to it as Aldeboran. In Chinese it is known as 畢宿五, in Hindu astronomy it is identified as the lunar mansion Rohini and as one of the twenty-seven daughters of Daksha and the wife of the god Chandra. This easily seen and striking star in its suggestive asterism is a subject for ancient. Mexican culture, For the Seris of northwestern Mexico, this star provides light for the seven women giving birth and it has three names, Hant Caalajc Ipápjö, Queeto, and Azoj Yeen oo Caap. The lunar month corresponding to October is called Queeto yaao Aldebarans path, aboriginal culture, in the Clarence River of northeastern New South Wales, this star is the Ancestor Karambal, who stole another mans wife. The womans husband tracked him down and burned the tree in which he was hiding and it is believed that he rose to the sky as smoke and became the star Aldebaran. On March 11, of 509 AD, an occultation of Aldebaran was observed in Athens. English astronomer Edmund Halley studied the timing of this event, and in 1718 concluded that Aldebaran must have changed position since that time and this, as well as observations of the changing positions of stars Sirius and Arcturus, led to the discovery of proper motion. Based on present day observations, the position of Aldebaran has shifted 7′ in the last 2000 years, note that 5,000 years ago the vernal equinox was close to Aldebaran. English astronomer William Herschel discovered a faint companion to Aldebaran in 1782 and this star was shown to be itself a close double star by S. W. Burnham in 1888, and he discovered an additional 14th magnitude companion at an angular separation of 31″. Follow on measurements of proper motion showed that Herschels companion was diverging from Aldebaran, however, the companion discovered by Burnham had almost exactly the same proper motion as Aldebaran, suggesting that the two formed a wide binary star system. Pickering at the Harvard College Observatory used a plate to capture fifty absorption lines in the spectrum of Aldebaran
3.
Lunar phase
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The lunar phase or phase of the moon is the shape of the illuminated portion of the Moon as seen by an observer on Earth. The lunar phases change cyclically as the Moon orbits the Earth, according to the positions of the Moon. The Moons rotation is locked by the Earths gravity, therefore the same lunar surface always faces Earth. This face is variously sunlit depending on the position of the Moon in its orbit, therefore, the portion of this hemisphere that is visible to an observer on Earth can vary from about 100% to 0%. The lunar terminator is the boundary between the illuminated and darkened hemispheres, each of the four intermediate lunar phases is roughly seven days but this varies slightly due to the elliptical shape of the Moons orbit. Aside from some craters near the lunar poles such as Shoemaker, all parts of the Moon see around 14.77 days of sunlight, in Western culture, the four principal lunar phases are new moon, first quarter, full moon, and third quarter. These are the instants when the Moons apparent geocentric celestial longitude minus the Suns apparent geocentric longitude is 0°, 90°, 180° and 270°. Each of these phases is instantaneous, lasting theoretically zero time, during the intervals between principal phases, the Moon appears either crescent-shaped or gibbous. These shapes, and the periods of time when the Moon shows them, are called the intermediate phases. They last, on average, one-quarter of a month, roughly 7.38 days, but their durations vary slightly because the Moons orbit is slightly elliptical. The descriptor waxing is used for a phase when the Moons apparent size is increasing, from new moon toward full moon. As the moon waxes, the lunar phases progress through new moon, crescent moon, first-quarter moon, gibbous moon, the moon is then said to wane as it passes through the gibbous moon, third-quarter moon, crescent moon and back to new moon. The terms old moon and new moon are not interchangeable, the old moon is a waning sliver until the moment it aligns with the sun and begins to wax, at which point it becomes new again. Half moon is used to mean the first- and third-quarter moons, while the term quarter refers to the extent of the moons cycle around the Earth. When a crescent Moon occurs, the phenomenon of earthshine may be apparent, in the Northern Hemisphere, if the left side of the Moon is dark then the light part is growing, and the Moon is referred to as waxing. If the right side of the Moon is dark then the part is shrinking. Assuming that the viewer is in the hemisphere, the right portion of the Moon is the part that is always growing. Nearer the Equator the Moon with its terminator will appear apparently horizontal during the morning and evening, the crescent Moon can open upward or downward, with the horns of the crescent pointing up or down, respectively
4.
Astronomy
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Astronomy is a natural science that studies celestial objects and phenomena. It applies mathematics, physics, and chemistry, in an effort to explain the origin of those objects and phenomena and their evolution. Objects of interest include planets, moons, stars, galaxies, and comets, while the phenomena include supernovae explosions, gamma ray bursts, more generally, all astronomical phenomena that originate outside Earths atmosphere are within the purview of astronomy. A related but distinct subject, physical cosmology, is concerned with the study of the Universe as a whole, Astronomy is the oldest of the natural sciences. The early civilizations in recorded history, such as the Babylonians, Greeks, Indians, Egyptians, Nubians, Iranians, Chinese, during the 20th century, the field of professional astronomy split into observational and theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects, theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. The two fields complement each other, with theoretical astronomy seeking to explain the results and observations being used to confirm theoretical results. Astronomy is one of the few sciences where amateurs can play an active role, especially in the discovery. Amateur astronomers have made and contributed to many important astronomical discoveries, Astronomy means law of the stars. Astronomy should not be confused with astrology, the system which claims that human affairs are correlated with the positions of celestial objects. Although the two share a common origin, they are now entirely distinct. Generally, either the term astronomy or astrophysics may be used to refer to this subject, however, since most modern astronomical research deals with subjects related to physics, modern astronomy could actually be called astrophysics. Few fields, such as astrometry, are purely astronomy rather than also astrophysics, some titles of the leading scientific journals in this field includeThe Astronomical Journal, The Astrophysical Journal and Astronomy and Astrophysics. In early times, astronomy only comprised the observation and predictions of the motions of objects visible to the naked eye, in some locations, early cultures assembled massive artifacts that possibly had some astronomical purpose. Before tools such as the telescope were invented, early study of the stars was conducted using the naked eye, most of early astronomy actually consisted of mapping the positions of the stars and planets, a science now referred to as astrometry. From these observations, early ideas about the motions of the planets were formed, and the nature of the Sun, Moon, the Earth was believed to be the center of the Universe with the Sun, the Moon and the stars rotating around it. This is known as the model of the Universe, or the Ptolemaic system. The Babylonians discovered that lunar eclipses recurred in a cycle known as a saros
5.
Computer-generated imagery
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The term CGI animation refers to dynamic CGI rendered as a movie. The term virtual world refers to agent-based, interactive environments, Computer graphics software is used to make computer-generated imagery for films, etc. Availability of CGI software and increased computer speeds have allowed artists and small companies to produce professional-grade films, games. This has brought about an Internet subculture with its own set of global celebrities, clichés, the evolution of CGI led to the emergence of virtual cinematography in the 1990s where runs of the simulated camera are not constrained by the laws of physics. Not only do animated images form part of computer-generated imagery, natural looking landscapes are generated via computer algorithms. A simple way to generate fractal surfaces is to use an extension of the triangular mesh method, relying on the construction of special case of a de Rham curve. The creation of a Brownian surface may be achieved not only by adding noise as new nodes are created, thus a topographical map with varying levels of height can be created using relatively straightforward fractal algorithms. Some typical, easy-to-program fractals used in CGI are the plasma fractal, modern architects use services from computer graphic firms to create 3-dimensional models for both customers and builders. These computer generated models can be accurate than traditional drawings. Architectural animation can also be used to see the relationship a building will have in relation to the environment. The rendering of architectural spaces without the use of paper and pencil tools is now an accepted practice with a number of computer-assisted architectural design systems. Architectural modeling tools allow an architect to visualize a space and perform walk-throughs in an interactive manner, Architectural modeling tools have now become increasingly internet-based. However, the quality of internet-based systems still lags behind those of sophisticated in-house modeling systems, in some applications, computer-generated images are used to reverse engineer historical buildings. Computer generated models used in animation are not always anatomically correct. However, organizations such as the Scientific Computing and Imaging Institute have developed anatomically correct computer-based models, Computer generated anatomical models can be used both for instructional and operational purposes. To date, a body of artist produced medical images continue to be used by medical students, such as images by Frank H. Netter. However, a number of anatomical models are becoming available. A single patient X-ray is not a computer generated image, even if digitized, however, in applications which involve CT scans a three-dimensional model is automatically produced from a large number of single slice x-rays, producing computer generated image
6.
Moon
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The Moon is an astronomical body that orbits planet Earth, being Earths only permanent natural satellite. It is the fifth-largest natural satellite in the Solar System, following Jupiters satellite Io, the Moon is second-densest satellite among those whose densities are known. The average distance of the Moon from the Earth is 384,400 km, the Moon is thought to have formed about 4.51 billion years ago, not long after Earth. It is the second-brightest regularly visible celestial object in Earths sky, after the Sun and its surface is actually dark, although compared to the night sky it appears very bright, with a reflectance just slightly higher than that of worn asphalt. Its prominence in the sky and its cycle of phases have made the Moon an important cultural influence since ancient times on language, calendars, art. The Moons gravitational influence produces the ocean tides, body tides, and this matching of apparent visual size will not continue in the far future. The Moons linear distance from Earth is currently increasing at a rate of 3.82 ±0.07 centimetres per year, since the Apollo 17 mission in 1972, the Moon has been visited only by uncrewed spacecraft. The usual English proper name for Earths natural satellite is the Moon, the noun moon is derived from moone, which developed from mone, which is derived from Old English mōna, which ultimately stems from Proto-Germanic *mǣnōn, like all Germanic language cognates. Occasionally, the name Luna is used, in literature, especially science fiction, Luna is used to distinguish it from other moons, while in poetry, the name has been used to denote personification of our moon. The principal modern English adjective pertaining to the Moon is lunar, a less common adjective is selenic, derived from the Ancient Greek Selene, from which is derived the prefix seleno-. Both the Greek Selene and the Roman goddess Diana were alternatively called Cynthia, the names Luna, Cynthia, and Selene are reflected in terminology for lunar orbits in words such as apolune, pericynthion, and selenocentric. The name Diana is connected to dies meaning day, several mechanisms have been proposed for the Moons formation 4.51 billion years ago, and some 60 million years after the origin of the Solar System. These hypotheses also cannot account for the angular momentum of the Earth–Moon system. This hypothesis, although not perfect, perhaps best explains the evidence, eighteen months prior to an October 1984 conference on lunar origins, Bill Hartmann, Roger Phillips, and Jeff Taylor challenged fellow lunar scientists, You have eighteen months. Go back to your Apollo data, go back to computer, do whatever you have to. Dont come to our conference unless you have something to say about the Moons birth, at the 1984 conference at Kona, Hawaii, the giant impact hypothesis emerged as the most popular. Afterward there were only two groups, the giant impact camp and the agnostics. Giant impacts are thought to have been common in the early Solar System, computer simulations of a giant impact have produced results that are consistent with the mass of the lunar core and the present angular momentum of the Earth–Moon system
7.
Star
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A star is a luminous sphere of plasma held together by its own gravity. The nearest star to Earth is the Sun, many other stars are visible to the naked eye from Earth during the night, appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth. Historically, the most prominent stars were grouped into constellations and asterisms, astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. However, most of the stars in the Universe, including all stars outside our galaxy, indeed, most are invisible from Earth even through the most powerful telescopes. Almost all naturally occurring elements heavier than helium are created by stellar nucleosynthesis during the stars lifetime, near the end of its life, a star can also contain degenerate matter. Astronomers can determine the mass, age, metallicity, and many properties of a star by observing its motion through space, its luminosity. The total mass of a star is the factor that determines its evolution. Other characteristics of a star, including diameter and temperature, change over its life, while the environment affects its rotation. A plot of the temperature of stars against their luminosities produces a plot known as a Hertzsprung–Russell diagram. Plotting a particular star on that allows the age and evolutionary state of that star to be determined. A stars life begins with the collapse of a gaseous nebula of material composed primarily of hydrogen, along with helium. When the stellar core is sufficiently dense, hydrogen becomes steadily converted into helium through nuclear fusion, the remainder of the stars interior carries energy away from the core through a combination of radiative and convective heat transfer processes. The stars internal pressure prevents it from collapsing further under its own gravity, a star with mass greater than 0.4 times the Suns will expand to become a red giant when the hydrogen fuel in its core is exhausted. In some cases, it will fuse heavier elements at the core or in shells around the core, as the star expands it throws a part of its mass, enriched with those heavier elements, into the interstellar environment, to be recycled later as new stars. Meanwhile, the core becomes a remnant, a white dwarf. Binary and multi-star systems consist of two or more stars that are bound and generally move around each other in stable orbits. When two such stars have a close orbit, their gravitational interaction can have a significant impact on their evolution. Stars can form part of a much larger gravitationally bound structure, historically, stars have been important to civilizations throughout the world
8.
Angular velocity
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This speed can be measured in the SI unit of angular velocity, radians per second, or in terms of degrees per second, degrees per hour, etc. Angular velocity is usually represented by the symbol omega, the direction of the angular velocity vector is perpendicular to the plane of rotation, in a direction that is usually specified by the right-hand rule. The angular velocity of a particle is measured around or relative to a point, called the origin. As shown in the diagram, if a line is drawn from the origin to the particle, then the velocity of the particle has a component along the radius, if there is no radial component, then the particle moves in a circle. On the other hand, if there is no cross-radial component, a radial motion produces no change in the direction of the particle relative to the origin, so, for the purpose of finding the angular velocity, the radial component can be ignored. Therefore, the rotation is completely produced by the perpendicular motion around the origin, the angular velocity in two dimensions is a pseudoscalar, a quantity that changes its sign under a parity inversion. The positive direction of rotation is taken, by convention, to be in the direction towards the y axis from the x axis, if the parity is inverted, but the orientation of a rotation is not, then the sign of the angular velocity changes. There are three types of angular velocity involved in the movement on an ellipse corresponding to the three anomalies, in three dimensions, the angular velocity becomes a bit more complicated. The angular velocity in case is generally thought of as a vector, or more precisely. It now has not only a magnitude, but a direction as well, the magnitude is the angular speed, and the direction describes the axis of rotation that Eulers rotation theorem guarantees must exist. The right-hand rule indicates the direction of the angular velocity pseudovector. Let u be a vector along the instantaneous rotation axis. This is the definition of a vector space, the only property that presents difficulties to prove is the commutativity of the addition. This can be proven from the fact that the velocity tensor W is skew-symmetric, therefore, R = e W t is a rotation matrix and in a time dt is an infinitesimal rotation matrix. Therefore, it can be expanded as R = I + W ⋅ d t +122 +, in such a frame, each vector is a particular case of the previous case, in which the module of the vector is constant. Though it just a case of a moving particle, this is a very important one for its relationship with the rigid body study. There are two ways to describe the angular velocity of a rotating frame, the angular velocity vector. Both entities are related and they can be calculated from each other, in a consistent way with the general definition, the angular velocity of a frame is defined as the angular velocity of each of the three vectors of the frame
9.
Minute and second of arc
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A minute of arc, arcminute, arc minute, or minute arc is a unit of angular measurement equal to 1/60 of one degree. Since one degree is 1/360 of a turn, one minute of arc is 1/21600 of a turn, a second of arc, arcsecond, or arc second is 1/60 of an arcminute, 1/3600 of a degree, 1/1296000 of a turn, and π/648000 of a radian. To express even smaller angles, standard SI prefixes can be employed, the number of square arcminutes in a complete sphere is 4 π2 =466560000 π ≈148510660 square arcminutes. The standard symbol for marking the arcminute is the prime, though a single quote is used where only ASCII characters are permitted. One arcminute is thus written 1′ and it is also abbreviated as arcmin or amin or, less commonly, the prime with a circumflex over it. The standard symbol for the arcsecond is the prime, though a double quote is commonly used where only ASCII characters are permitted. One arcsecond is thus written 1″ and it is also abbreviated as arcsec or asec. In celestial navigation, seconds of arc are used in calculations. This notation has been carried over into marine GPS receivers, which normally display latitude and longitude in the format by default. An arcsecond is approximately the angle subtended by a U. S. dime coin at a distance of 4 kilometres, a milliarcsecond is about the size of a dime atop the Eiffel Tower as seen from New York City. A microarcsecond is about the size of a period at the end of a sentence in the Apollo mission manuals left on the Moon as seen from Earth, since antiquity the arcminute and arcsecond have been used in astronomy. The principal exception is Right ascension in equatorial coordinates, which is measured in units of hours, minutes. These small angles may also be written in milliarcseconds, or thousandths of an arcsecond, the unit of distance, the parsec, named from the parallax of one arcsecond, was developed for such parallax measurements. It is the distance at which the radius of the Earths orbit would subtend an angle of one arcsecond. The ESA astrometric space probe Gaia is hoped to measure star positions to 20 microarcseconds when it begins producing catalog positions sometime after 2016, there are about 1.3 trillion µas in a turn. Currently the best catalog positions of stars actually measured are in terms of milliarcseconds, apart from the Sun, the star with the largest angular diameter from Earth is R Doradus, a red supergiant with a diameter of 0.05 arcsecond. The dwarf planet Pluto has proven difficult to resolve because its angular diameter is about 0.1 arcsecond, space telescopes are not affected by the Earths atmosphere but are diffraction limited. For example, the Hubble space telescope can reach a size of stars down to about 0. 1″
10.
Angular diameter
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The angular diameter or apparent size is an angular measurement describing how large a sphere or circle appears from a given point of view. In the vision sciences it is called the angle and in optics it is the angular aperture. The angular diameter can alternatively be thought of as the angle through which an eye or camera must rotate to look from one side of an apparent circle to the opposite side, Angular radius equals half the angular diameter. When D ≫ d, we have δ ≈ d / D, for practical use, the distinction is only significant for spherical objects that are relatively close, since the small-angle approximation holds for x ≪1, arcsin x ≈ arctan x ≈ x. Estimates of angular diameter may be obtained by holding the hand at right angles to an extended arm. In astronomy the sizes of objects in the sky are given in terms of their angular diameter as seen from Earth. Since these angular diameters are typically small, it is common to present them in arcseconds, an arcsecond is 1/3600th of one degree, and a radian is 180/ π degrees, so one radian equals 3600*180/ π arcseconds, which is about 206265 arcseconds. Therefore, the diameter of an object with physical diameter d at a distance D, expressed in arcseconds, is given by. These objects have a diameter of one arcsecond, an object of diameter 725. The angular diameter of the Sun, from a distance of one light-year, is 0. 03″, the angular diameter 0. 03″ of the Sun given above is approximately the same as that of a person at a distance of the diameter of the Earth. Thus the angular diameter of the Sun is about 250,000 times that of Sirius, the angular diameter of the Sun is also about 250,000 times that of Alpha Centauri A. The angular diameter of the Sun is about the same as that of the Moon, even though Pluto is physically larger than Ceres, when viewed from Earth Ceres has a much larger apparent size. While angular sizes measured in degrees are useful for larger patches of sky, we need much finer units when talking about the size of galaxies. The Moons motion across the sky can be measured in size, approximately 15 degrees every hour. A one-mile-long line painted on the face of the Moon would appear to us to be about one arc-second in length, in astronomy, it is typically difficult to directly measure the distance to an object. But the object may have a physical size and a measurable angular diameter. In that case, the angular diameter formula can be inverted to yield the Angular diameter distance to distant objects as d ≡2 D tan . In non-Euclidean space, such as our universe, the angular diameter distance is only one of several definitions of distance
11.
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
12.
Orbit of the Moon
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Not to be confused with Lunar orbit. The Moon orbits Earth in the direction and completes one revolution relative to the stars in approximately 27.323 days. Earth and the Moon orbit about their barycentre, which lies about 4,600 km from Earths center, on average, the Moon is at a distance of about 385,000 km from Earths centre, which corresponds to about 60 Earth radii. With a mean velocity of 1.022 km/s, the Moon appears to move relative to the stars each hour by an amount roughly equal to its angular diameter. The Moon differs from most satellites of planets in that its orbit is close to the plane of the ecliptic. The plane of the orbit is inclined to the ecliptic by about 5°. The properties of the orbit described in this section are approximations, the Moons orbit around Earth has many irregularities, whose study has a long history. The orbit of the Moon is distinctly elliptical, with an eccentricity of 0.0549. The non-circular form of the lunar orbit causes variations in the Moons angular speed and apparent size as it moves towards, the mean angular movement relative to an imaginary observer at the barycentre is 13. 176° per day to the east. The Moons elongation is its angular distance east of the Sun at any time, at new moon, it is zero and the Moon is said to be in conjunction. At full moon, the elongation is 180° and it is said to be in opposition, in both cases, the Moon is in syzygy, that is, the Sun, Moon and Earth are nearly aligned. When elongation is either 90° or 270°, the Moon is said to be in quadrature, the orientation of the orbit is not fixed in space, but rotates over time. This orbital precession is also called apsidal precession and is the rotation of the Moons orbit within the orbital plane, the Moons apsidal precession is distinct from, and should not be confused with its axial precession. The mean inclination of the orbit to the ecliptic plane is 5. 145°. The rotational axis of the Moon is also not perpendicular to its plane, so the lunar equator is not in the plane of its orbit. Therefore, the angle between the ecliptic and the equator is always 1. 543°, even though the rotational axis of the Moon is not fixed with respect to the stars. The period from moonrise to moonrise at the poles is quite close to the sidereal period, when the sun is the furthest below the horizon, the moon will be full when it is at its highest point. The nodes are points at which the Moons orbit crosses the ecliptic, the Moon crosses the same node every 27.2122 days, an interval called the draconic or draconitic month
13.
Regulus
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Regulus, also designated Alpha Leonis, is the brightest star in the constellation of Leo and one of the brightest stars in the night sky, lying approximately 79 light years from the Sun. Regulus is a star system composed of four stars that are organized into two pairs. The spectroscopic binary Regulus A consists of a blue-white main-sequence star and its companion, which has not yet been directly observed, located farther away are Regulus B, C, and D, which are dim main-sequence stars. α Leonis is the stars Bayer designation, the traditional name Rēgulus is Latin for prince or little king. 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 Regulus for this star. It is now so entered in the IAU Catalog of Star Names, Regulus is 0.46 degree from the ecliptic, the closest of the bright stars, and is regularly occulted by the Moon. Occultations by the planets Mercury and Venus are possible but rare, the last occultation of Regulus by a planet was on July 7,1959, by Venus. The next will occur on October 1,2044, also by Venus, other planets will not occult Regulus over the next few millennia because of their node positions. An occultation of Regulus by the asteroid 166 Rhodope was observed by 12 researchers from Portugal, Spain, Italy, differential bending of light was measured to be consistent with general relativity. Regulus was occulted by the asteroid 163 Erigone in the morning of March 20,2014. The center of the shadow passed through New York and eastern Ontario. The International Occultation Timing Association recorded no observations at all, Regulus passes through SOHOs LASCO C3 every August. For most Earth observers, the rising of Regulus occurs in the first week of September. Every 8 years, Venus passes Regulus around the time of the heliacal rising. Regulus is a star system consisting of at least four stars. Regulus A is the dominant star, with a binary companion 177 distant that is thought to be physically related, Regulus D is a 12th magnitude companion at 212, which shares a common motion with the other stars. Regulus A is a star consisting of a blue-white main sequence star of spectral type B7V, which is orbited by a star of at least 0.3 solar masses. The two stars take approximately 40 days to complete an orbit around their common centre of mass, in other words, Keplers third law, which holds exactly only for two point-like masses, would be no longer valid because of the highly distorted shape of the primary
14.
Spica
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Spica, also designated Alpha Virginis, is the brightest star in the constellation of Virgo and the 16th brightest star in the night sky. Analysis of its shows that it is located 250 ±10 light years from the Sun. The primary is a giant and a variable star of the Beta Cephei type. Spica, along with Denebola or Regulus depending on the source and Arcturus, is part of the Spring Triangle asterism, as one of the nearest massive binary star systems to the Sun, Spica has been the subject of many observational studies. Spica is believed to be the star that gave Hipparchus the data led him to discover the precession of the equinoxes. A temple to Menat at Thebes was oriented with reference to Spica when it was built in 3200 BC, nicolaus Copernicus made many observations of Spica with his home-made triquetrum for his researches on precession. Spica is 2.05 degrees from the ecliptic and can be occulted by the Moon, the last planetary occultation of Spica occurred when Venus passed in front of the star on November 10,1783. The next occultation will occur on September 2,2197, when Venus again passes in front of Spica, the Sun passes a little more than 2° north of Spica around October 16 every year, and the stars heliacal rising occurs about two weeks later. Every 8 years, Venus passes Spica around the time of the heliacal rising. A method of finding Spica is to follow the arc of the handle of the Big Dipper to Arcturus and this can be recalled by the mnemonic phrase, arc to Arcturus and spike to Spica. Spica is a binary star whose components orbit about each other every four days. They stay close together that they cannot be resolved as two stars through a telescope. The changes in the motion of this pair results in a Doppler shift in the absorption lines of their respective spectra. Initially, the parameters for this system were inferred using spectroscopic measurements. The primary star has a classification of B1 III–IV. The luminosity class matches the spectrum of a star that is midway between a subgiant and a giant star, and it is no longer a B-type main-sequence star and this is a massive star with more than 10 times the mass of the Sun and seven times the Suns radius. The total luminosity of this star is about 12,100 times that of the Sun, the primary is one of the nearest stars to the Sun that has enough mass to end its life in a Type II supernova explosion. The primary is classified as a Beta Cephei-type variable star that varies in brightness over a 0. 1738-day period, the spectrum shows a radial velocity variation with the same period, indicating that the surface of the star is regularly pulsating outward and then contracting
15.
Antares
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Distinctly reddish when viewed with the unaided eye, Antares is a red supergiant of spectral type M1. 5Iab and is one of the largest known stars. It is an irregular variable star with a quoted magnitude range of +0.6 to +1.6. Antares is the brightest, most massive, and most evolved stellar member of the nearest OB association, Antares is a member of the Upper Scorpius subgroup of the Scorpius–Centaurus Association, which contains thousands of stars with mean age 11 million years at a distance of approximately 145 parsecs. Antares is a supergiant star with a classification of M1. 5Iab. Based upon parallax measurements, Antares is approximately 550 light-years from the Sun, the mass of the star has been calculated to be in the range of 15 to 18 solar masses. The size of Antares may be calculated using its parallax and angular diameter, the parallax angle is given in the adjacent box, and the angular diameter is known from lunar occultation measurements. This implies a radius of 890 ±150 solar radii at this distance, by analysing its radial velocity from its spectrum, Pugh and colleagues calculated a period of 5.93 ±0.01 years and considered whether this change was orbital or pulsational. If the latter, then the radius of the changes by 165 ±22 solar radii. However, if this were the case, Antares brightness would vary by a greater amount, Antares is a type LC slow irregular variable star, whose apparent magnitude slowly varies from +0.6 to +1.6. Antares is visible in the sky all night around May 31 of each year, at this time, Antares rises at dusk and sets at dawn as seen at the equator. Antares is one of the four first magnitude stars that lies within 5° of the ecliptic and therefore can be occulted by the Moon and, though rarely, by Venus. The last occultation of Antares by Venus took place on September 17,525 BC, on 31 July 2009, Antares was occulted by the Moon. The event was visible in much of southern Asia and the Middle East, every year around December 2 the Sun passes 5° north of Antares. Antares has a magnitude 5.5 companion star, Antares B and it was first observed by Scottish astronomer James William Grant FRSE while in India on 23 July 1844. The last is equal to a separation of about 529 astronomical units at the estimated distance of Antares. Spectroscopic examination of the states in the outflow of matter from the companion star suggests that it is about 224 au beyond the primary. Antares B is a blue-white main-sequence star of spectral type B2. 5V, the companion star is normally difficult to see in small telescopes due to glare from Antares A, but can sometimes be seen in apertures over 150 millimetres. Antares B can sometimes be observed with a telescope for a few seconds during lunar occultations while Antares A is hidden by the Moon
16.
Pollux (star)
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Pollux, also designated Beta Geminorum, is an orange-hued evolved giant star approximately 34 light-years from the Sun in the northern constellation of Gemini. It is the closest giant star to the Sun, since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified. In 2006, a planet was confirmed to be orbiting it. β Geminorum is the stars Bayer designation, the traditional name Pollux refers specifically to the twins Castor and Pollux in Greek and Roman mythology. 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 Pollux for this star. Castor and Pollux are the two heavenly twin stars giving the constellation Gemini its name, the stars, however, are quite different in detail. Castor is a sextuple system of hot, bluish-white A-type stars and dim red dwarfs, while Pollux is a single. In Percy Shelleys 1818 poem Homers Hymn To Castor And Pollux, following its discovery the planet was designated Pollux b. In July 2014 the International Astronomical Union launched a process for giving proper names to certain exoplanets, the process involved public nomination and voting for the new names. In December 2015, the IAU announced the name was Thestias for this planet. The winning name was based on that submitted by theSkyNet of Australia, namely Leda. At the request of the IAU, Thestias was substituted and this was because Leda was already attributed to an asteroid and to one of Jupiters satellites. In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Muekher al Dzira, in Chinese, 北河, meaning North River, refers to an asterism consisting of Pollux, ρ Geminorum and Castor. Consequently, Pollux itself is known as 北河三 Parallax measurements made with the Hipparcos astrometry satellite place Pollux at a distance of about 33.78 light-years from the Sun. At an apparent visual magnitude of 1.1, Pollux is the brightest star in the constellation, the star is larger than the Sun, with about two times its mass and almost nine times its radius. Once an A-type main sequence star, Pollux has exhausted the hydrogen at its core, the effective temperature of this stars outer envelope is about 4666 K, which lies in the range that produces the characteristic orange hue of K-type stars. Pollux has a rotational velocity of 2.8 km·s−1. The abundance of other than hydrogen and helium, what astronomers term the stars metallicity, is somewhat uncertain
17.
Deep-sky object
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Deep-sky objects are astronomical objects other than individual stars and Solar System objects. The classification is used for the most part by amateur astronomers to denote visually observed faint naked eye and telescopic objects such as clusters, nebulae. Classifying non-stellar astronomical objects began soon after the invention of the telescope, as telescopes improved these faint nebulae would be broken into more descriptive scientific classifications such as interstellar clouds, star clusters, and galaxies. Deep-sky object, as a classification for these objects, has its origins in the modern field of amateur astronomy. There are many amateur astronomical techniques and activities associated with deep-sky objects, some of these objects are bright enough to find and see in binoculars and small telescopes. But the faintest objects need the power of telescopes with large objectives. Observing faint objects needs dark skies, so these relatively portable types of telescopes also lend themselves to the majority of amateurs who need to travel outside light polluted urban locations. To cut down light pollution and enhance contrast observers employ nebular filters designed to admit certain wavelength, there are organized activities associated with DSOs such as the Messier marathon which occurs at a specific time each year and involve observers trying to spot all 110 Messier objects in one night. Since the Messier catalog objects were discovered with relatively small 18th century telescopes it is a popular list with observers, a much more demanding test known as the Herschel 400 is designed to tax larger telescopes and experienced amateur astronomers. There are many astronomical object types that come under the description of deep-sky objects, Jess K. Gilmour, The practical astronomers deep-sky companion. W. H. Finlay, Concise Catalog of Deep-sky Objects, Astrophysical Information for 500 Galaxies, Clusters, includes the Messier objects, Herschel 400 & more. Roger Nelson Clark, Visual astronomy of the deep sky, burnhams Celestial Handbook by Robert Burnham, Jr. Deep Sky Observers Guide by Neil Bone, Wil Tirion, the practical astronomers deep-sky companion by Jess K. Gilmour. Concise Catalog of Deep-sky Objects, Astrophysical Information for 500 Galaxies, Clusters, includes the Messier objects, Herschel 400 & more Visual astronomy of the deep sky by Roger Nelson Clark
18.
Pleiades
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In astronomy, the Pleiades, or Seven Sisters, is an open star cluster containing middle-aged, hot B-type stars located in the constellation of Taurus. It is among the nearest star clusters to Earth and is the cluster most obvious to the eye in the night sky. The celestial entity has several meanings in different cultures and traditions, the cluster is dominated by hot blue and extremely luminous stars that have formed within the last 100 million years. Computer simulations have shown that the Pleiades was probably formed from a configuration that resembled the Orion Nebula. Astronomers estimate that the cluster will survive for about another 250 million years, the name of the Pleiades comes from Ancient Greek. It probably derives from plein because of the importance in delimiting the sailing season in the Mediterranean Sea. However, the name was later mythologised as the name of seven sisters, whose name was imagined to derive from that of their mother Pleione. In reality, the name of the star cluster almost certainly came first, in Hinduism, the Pleiades are known as Krittika and are associated with the war-god Kartikeya, who derives his name from them. The god is raised by the six Krittika sisters, also known as the Matrikas and he is said to have developed a face for each of them. The Ancient Egyptians may have used the names Followers and Ennead in the texts of the Calendar of Lucky and Unlucky Days of papyrus Cairo 86637. The earliest known depiction of the Pleiades is likely a bronze age known as the Nebra sky disk. Some Greek astronomers considered them to be a constellation, and they are mentioned by Hesiods Works and Days. They are also mentioned three times in the Bible, some scholars of Islam suggested that the Pleiades are the stars mentioned in the sura Najm of the Quran. In Japan, the constellation is mentioned under the name Mutsuraboshi in the 8th century Kojiki, the constellation is now known in Japan as Subaru. It was chosen as the name of Subaru automobiles to reflect the origins of the firm as the joining of five companies. The rising of the Pleiades is mentioned in the Ancient Greek text Geoponica, the Greeks oriented the Hecatompedon temple of 550 BC and the Parthenon of 438 BC to their rising. The rising of the Pleiades before dawn has long regarded as the start of the new year in Māori culture. The rising of Matariki is celebrated as a festival in New Zealand
19.
Binary star
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A binary star is a star system consisting of two stars orbiting around their common barycenter. Systems of two or more stars are called multiple star systems and these systems, especially when more distant, often appear to the unaided eye as a single point of light, and are then revealed as multiple by other means. Research over the last two centuries suggests that half or more of visible stars are part of star systems. The term double star is used synonymously with binary star, however. Optical doubles are so called because the two stars close together in the sky as seen from the Earth, they are almost on the same line of sight. Nevertheless, their doubleness depends only on this effect, the stars themselves are distant from one another. A double star can be revealed as optical by means of differences in their measurements, proper motions. Most known double stars have not been studied closely to determine whether they are optical doubles or they are doubles physically bound through gravitation into a multiple star system. This also determines an empirical mass-luminosity relationship from which the masses of stars can be estimated. Binary stars are often detected optically, in case they are called visual binaries. Many visual binaries have long periods of several centuries or millennia. They may also be detected by indirect techniques, such as spectroscopy or astrometry, if components in binary star systems are close enough they can gravitationally distort their mutual outer stellar atmospheres. In some cases, these close binary systems can exchange mass, examples of binaries are Sirius, and Cygnus X-1. Binary stars are common as the nuclei of many planetary nebulae. This should be called a double star, and any two stars that are thus mutually connected, form the binary sidereal system which we are now to consider. By the modern definition, the binary star is generally restricted to pairs of stars which revolve around a common center of mass. Binary stars which can be resolved with a telescope or interferometric methods are known as visual binaries, for most of the known visual binary stars one whole revolution has not been observed yet, they are observed to have travelled along a curved path or a partial arc. The more general term double star is used for pairs of stars which are seen to be together in the sky
20.
Effective temperature
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The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is used as an estimate of a bodys surface temperature when the bodys emissivity curve is not known. When the stars or planets net emissivity in the relevant wavelength band is less than unity, the net emissivity may be low due to surface or atmospheric properties, including greenhouse effect. Notice that the luminosity of a star is then L =4 π R2 σ T e f f 4. The definition of the radius is obviously not straightforward. More rigorously the effective temperature corresponds to the temperature at the radius that is defined by a value of the Rosseland optical depth within the stellar atmosphere. The effective temperature and the bolometric luminosity are the two fundamental physical parameters needed to place a star on the Hertzsprung–Russell diagram, both effective temperature and bolometric luminosity depend on the chemical composition of a star. The effective temperature of our Sun is around 5780 kelvin, stars have a decreasing temperature gradient, going from their central core up to the atmosphere. The core temperature of the temperature at the centre of the sun where nuclear reactions take place—is estimated to be 15,000,000 K. The effective temperature of a star indicates the amount of heat that the star radiates per unit of surface area, from the warmest surfaces to the coolest is the sequence of star types known as O, B, A, F, G, K, and M. The effective temperature of a planet can be calculated by equating the power received by the planet with the emitted by a blackbody of temperature T. Take the case of a planet at a distance D from the star and we also allow the planet to reflect some of the incoming radiation by incorporating a parameter called the albedo. An albedo of 1 means that all the radiation is reflected, the effective temperature for Jupiter from this calculation is 112 K and 51 Pegasi b is 1258 K. A better estimate of effective temperature for some planets, such as Jupiter, the actual temperature depends on albedo and atmosphere effects. The actual temperature from spectroscopic analysis for HD209458 b is 1130 K, the internal heating within Jupiter raises the effective temperature to about 152 K. The surface temperature of a planet can be estimated by modifying the effective-temperature calculation to account for emissivity and this area intercepts some of the power which is spread over the surface of a sphere of radius D. We also allow the planet to some of the incoming radiation by incorporating a parameter a called the albedo. An albedo of 1 means that all the radiation is reflected, there is also a factor ε, which is the emissivity and represents atmospheric effects
21.
3C 273
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3C273 is a quasar located in the constellation Virgo. It was the first quasar ever to be identified and it is the optically brightest quasar in the sky, and one of the closest with a redshift, z, of 0.158. A luminosity distance of DL =749 megaparsecs may be calculated from z. It is also one of the most luminous quasars known, with a magnitude of −26.7. Since the suns absolute magnitude is 4.83, it means that the quasar is over 4 trillion times more luminous than the Sun at visible wavelengths. The mass of its black hole has been measured to be 886 ±187 million solar masses through broad emission-line reverberation mapping. The quasar has a large-scale visible jet, which measures ~200 kly long, having an apparent size of 23″, in 1995 optical imaging of the jet using the Hubble Space Telescope revealed a structured morphology evidenced by repeated bright knots interlaced by areas of weak emission. The name signifies that it was the 273rd object of the Third Cambridge Catalog of Radio Sources, published in 1959. In 1963, Maarten Schmidt and Bev Oke published a pair of papers in Nature reporting that 3C273 has a redshift of 0.158. Prior to the discovery of 3C273, several other sources had been associated with optical counterparts. Also, many active galaxies had been misidentified as variable stars, including the famous BL Lac, W Com, however, it wasnt understood what these objects were, since their spectra were unlike those of any known stars. Its spectrum did not resemble that of any stars with typical stellar elements. 3C273 was the first object to be identified as what we now know quasars to be — extremely luminous objects at cosmological distances, 3C273 is a radio-loud quasar, and was also one of the first extragalactic X-ray sources discovered in 1970. However, even to this day, the process gives rise to the X-ray emissions is controversial. The luminosity is variable at nearly every wavelength from radio waves to Gamma rays on timescales of a few days to decades, such jets are believed to be created by the interaction of the central black hole and the accretion disk. VLBI radio observations of 3C273 have revealed proper motion of some of the radio emitting regions, 3C273 lies at the center of a giant elliptical galaxy with an apparent magnitude of 16 and an apparent size of 30 arc seconds. 3C273 is visible in May in both the northern and southern hemispheres, situated in the Virgo constellation, It is bright enough to be observed with larger amateur telescopes. Given its distance from Earth and visual magnitude, 3C273 is the most distant celestial object average amateur astronomers are likely to see through their telescopes
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Maarten Schmidt
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Maarten Schmidt is a Dutch astronomer who measured the distances of quasars. Born in Groningen, The Netherlands, Schmidt studied with Jan Hendrik Oort and he earned his Ph. D. degree from Leiden Observatory in 1956. He was a co-recipient, with Donald Lynden-Bell, of the inaugural Kavli Prize for Astrophysics in 2008, in 1959, he emigrated to the United States and went to work at the California Institute of Technology. In the beginning, he worked on theories about the mass distribution, of particular note from this period was his formulation of what has become known as the Schmidt law, which relates the density of interstellar gas to the rate of star formation occurring in that gas. He later began a study of the spectra of radio sources. Schmidt termed 3C273 a quasi-stellar object or quasar, thousands have since been identified, named after him Asteroid 10430 Martschmidt
23.
Quasar
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A quasar is an active galactic nucleus of very high luminosity. A quasar consists of a black hole surrounded by an orbiting accretion disk of gas. As gas in the accretion disk falls toward the black hole, quasars emit energy across the electromagnetic spectrum and can be observed at radio, infrared, visible, ultraviolet, and X-ray wavelengths. The most powerful quasars have luminosities exceeding 1041 W, thousands of greater than the luminosity of a large galaxy such as the Milky Way. Quasars are found over a broad range of distances. The peak epoch of quasar activity in the Universe corresponds to redshifts around 2, as of 2011, the most distant known quasar is at redshift z=7.085, light observed from this quasar was emitted when the Universe was only 770 million years old. Because quasars are distant objects, any light which reaches the Earth is redshifted due to the expansion of space. In early optical images, quasars appeared as point sources, indistinguishable from stars, with infrared telescopes and the Hubble Space Telescope, the host galaxies surrounding the quasars have been detected in some cases. These galaxies are normally too dim to be seen against the glare of the quasar, most quasars, with the exception of 3C273 whose average apparent magnitude is 12.9, cannot be seen with small telescopes. The luminosity of some quasars changes rapidly in the optical range, because these changes occur very rapidly they define an upper limit on the volume of a quasar, quasars are not much larger than the Solar System. This implies a high power density. The mechanism of brightness changes probably involves relativistic beaming of astrophysical jets pointed nearly directly toward Earth, the highest redshift quasar known is ULAS J1120+0641, with a redshift of 7.085, which corresponds to a comoving distance of approximately 29 billion light-years from Earth. Since light cannot escape the black holes, the energy is actually generated outside the event horizon by gravitational stresses. Central masses of 105 to 109 solar masses have been measured in quasars by using reverberation mapping. The matter accreting onto the hole is unlikely to fall directly in. Quasars may also be ignited or re-ignited when normal galaxies merge, in fact, it has been suggested that a quasar could form as the Andromeda Galaxy collides with our own Milky Way galaxy in approximately 3–5 billion years. More than 200,000 quasars are known, most from the Sloan Digital Sky Survey, all observed quasar spectra have redshifts between 0.056 and 7.085. Applying Hubbles law to these redshifts, it can be shown that they are between 600 million and 28.85 billion light-years away
24.
Solar eclipse
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As seen from the Earth, a solar eclipse is a type of eclipse that occurs when the Moon passes between the Sun and Earth, and the Moon fully or partially blocks the Sun. This can happen only at new moon when the Sun and the Moon are in conjunction as seen from Earth in an alignment referred to as syzygy, in a total eclipse, the disk of the Sun is fully obscured by the Moon. In partial and annular eclipses, only part of the Sun is obscured, if the Moon were in a perfectly circular orbit, a little closer to the Earth, and in the same orbital plane, there would be total solar eclipses every month. However, the Moons orbit is inclined at more than 5 degrees to the Earths orbit around the Sun, Earths orbit is called the ecliptic plane as the Moons orbit must cross this plane in order for an eclipse to occur. In addition, the Moons actual orbit is elliptical, often taking it far away from Earth that its apparent size is not large enough to block the Sun totally. The orbital planes cross each other at a line of nodes resulting in at least two, and up to five, solar eclipses occurring each year, no more than two of which can be total eclipses. However, total solar eclipses are rare at any particular location because totality exists only along a path on the Earths surface traced by the Moons shadow or umbra. An eclipse is a natural phenomenon, nevertheless, in some ancient and modern cultures, solar eclipses have been attributed to supernatural causes or regarded as bad omens. A total solar eclipse can be frightening to people who are unaware of its explanation, as the Sun seems to disappear during the day. People referred to as eclipse chasers or umbraphiles will travel to locations to observe or witness predicted central solar eclipses. For the date of the next eclipse see the section Recent, during any one eclipse, totality occurs at best only in a narrow track on the surface of Earth. An annular eclipse occurs when the Sun and Moon are exactly in line with the Earth, hence the Sun appears as a very bright ring, or annulus, surrounding the dark disk of the Moon. A hybrid eclipse shifts between a total and annular eclipse, at certain points on the surface of Earth, it appears as a total eclipse, whereas at other points it appears as annular. A partial eclipse occurs when the Sun and Moon are not exactly in line with the Earth and this phenomenon can usually be seen from a large part of the Earth outside of the track of an annular or total eclipse. However, some eclipses can only be seen as an eclipse, because the umbra passes above the Earths polar regions. Partial eclipses are virtually unnoticeable in terms of the suns brightness, even at 99%, it would be no darker than civil twilight. Of course, partial eclipses can be observed if one is viewing the sun through a darkening filter, the Suns distance from Earth is about 400 times the Moons distance, and the Suns diameter is about 400 times the Moons diameter. Because these ratios are approximately the same, the Sun and the Moon as seen from Earth appear to be approximately the same size, about 0.5 degree of arc in angular measure
25.
Rhea (moon)
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Rhea is the second-largest moon of Saturn and the ninth-largest moon in the Solar System. It is the second smallest body in the Solar System, after the asteroid and dwarf planet Ceres and it was discovered in 1672 by Giovanni Domenico Cassini. Rhea was discovered by Giovanni Domenico Cassini on 23 December 1672 and it was the third moon discovered around Saturn and the second by him. Rhea is named after the Titan Rhea of Greek mythology, the mother of the gods and it is also designated Saturn V. Cassini named the four moons he discovered Sidera Lodoicea to honor King Louis XIV. Astronomers fell into the habit of referring to them and Titan as Saturn I through Saturn V, once Mimas and Enceladus were discovered, in 1789, the numbering scheme was extended to Saturn VII. Rhea is an icy body with a density of about 1.236 g/cm3 and this low density indicates that it is made of ~25% rock and ~75% water ice. Although Rhea is the ninth-largest moon, it is only the tenth-most-massive moon, earlier it was assumed that Rhea had a rocky core in the center. However measurements taken during a flyby by the Cassini orbiter in 2005 cast this into doubt. In a paper published in 2007 it was claimed that the axial dimensionless moment of inertia coefficient was 0.4, such a value indicated that Rhea had an almost homogeneous interior while the existence of a rocky core would imply a moment of inertia of about 0.34. In the same year another paper claimed the moment of inertia was about 0.37 implying that Rhea was partially differentiated. A year later yet another paper claimed that the moon may not be in equilibrium meaning that the moment of inertia can not be determined from the gravity data alone. In 2008 an author of the first paper tried to reconcile these three disparate results.4, again implying a homogeneous interior, the triaxial shape of Rhea is consistent with a homogeneous body in hydrostatic equilibrium rotating at Rheas angular velocity. Rheas features resemble those of Dione, with leading and trailing hemispheres, suggesting similar composition. The temperature on Rhea is 99 K in direct sunlight and between 73 K and 53 K in the shade, Rhea has two very large impact basins on its anti-Cronian hemisphere, which are about 400 and 500 km across. The more northerly and less degraded of the two, called Tirawa, is comparable to the basin Odysseus on Tethys. There is a 48 km-diameter impact crater at 112°W that is prominent because of a system of bright rays. This crater, called Inktomi, is nicknamed The Splat, no evidence of any endogenic activity has been discovered. This suggests that a major resurfacing event occurred some time during its formation, the leading hemisphere is heavily cratered and uniformly bright
26.
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
27.
Dione (moon)
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Dione is a moon of Saturn. It was discovered by Italian astronomer Giovanni Domenico Cassini in 1684 and it is named after the Titaness Dione of Greek mythology. It is also designated Saturn IV, Giovanni Domenico Cassini named the four moons he discovered Sidera Lodoicea to honor king Louis XIV. Cassini found Dione in 1684 using a large aerial telescope he set up on the grounds of the Paris Observatory, Dione orbits Saturn with a semimajor axis about 2% less than that of the Moon. However, reflecting Saturns greater mass, Diones orbital period is one tenth that of the Moon, Dione is currently in a 1,2 mean-motion orbital resonance with moon Enceladus, completing one orbit of Saturn for every two orbits completed by Enceladus. The resonance also maintains a smaller eccentricity in Diones orbit, tidally heating it as well, Dione has two co-orbital, or trojan, moons, Helene and Polydeuces. They are located within Diones Lagrangian points L4 and L5,60 degrees ahead of, at 1122 km in diameter, Dione is the 15th largest moon in the Solar System, and is more massive than all known moons smaller than itself combined. About two thirds of Diones mass is water ice, and the remaining is a dense core, data gathered by Cassini indicates that Dione has an internal liquid water ocean. Downward bending of the associated with the 1.5 km high ridge Janiculum Dorsa can most easily be explained by the presence of such an ocean. Gravity and shape data points to a 99 ±23 km thick ice shell crust on top of a 65 ±30 internal liquid water global ocean, neither moon has a shape close to hydrostatic equilibrium, the deviations are maintained by isostasy. Diones ice shell is thought to vary in thickness by less than 5%, with the thinnest areas at the poles, though somewhat smaller and denser, Dione is otherwise very similar to Rhea. They both have similar features and varied terrain, and both have dissimilar leading and trailing hemispheres. Diones leading hemisphere is heavily cratered and is uniformly bright and its trailing hemisphere, however, contains an unusual and distinctive surface feature, a network of bright ice cliffs. The origin of these features was mysterious, because all that was known was that the material has an albedo and is thin enough that it does not obscure the surface features underneath. Later, after the activity and resurfacing ceased, cratering continued primarily on the leading hemisphere. This hypothesis was proven wrong by the Cassini probe flyby of December 13,2004 and these revealed that the wisps were, in fact, not ice deposits at all, but rather bright ice cliffs created by tectonic fractures. Dione has been revealed as a world riven by enormous fractures on its trailing hemisphere. The Cassini orbiter performed a flyby of Dione at 500 km on October 11,2005
28.
Venus
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Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. It has the longest rotation period of any planet in the Solar System and it is named after the Roman goddess of love and beauty. It is the second-brightest natural object in the sky after the Moon, reaching an apparent magnitude of −4.6. Because Venus orbits within Earths orbit it is a planet and never appears to venture far from the Sun. Venus is a planet and is sometimes called Earths sister planet because of their similar size, mass, proximity to the Sun. It is radically different from Earth in other respects and it has the densest atmosphere of the four terrestrial planets, consisting of more than 96% carbon dioxide. The atmospheric pressure at the surface is 92 times that of Earth. Venus is by far the hottest planet in the Solar System, with a surface temperature of 735 K. Venus is shrouded by an layer of highly reflective clouds of sulfuric acid. It may have had water oceans in the past, but these would have vaporized as the temperature rose due to a greenhouse effect. The water has probably photodissociated, and the hydrogen has been swept into interplanetary space by the solar wind because of the lack of a planetary magnetic field. Venuss surface is a dry desertscape interspersed with rocks and is periodically resurfaced by volcanism. As one of the brightest objects in the sky, Venus has been a fixture in human culture for as long as records have existed. It has been sacred to gods of many cultures, and has been a prime inspiration for writers and poets as the morning star. Venus was the first planet to have its motions plotted across the sky, as the closest planet to Earth, Venus has been a prime target for early interplanetary exploration. It was the first planet beyond Earth visited by a spacecraft, Venuss thick clouds render observation of its surface impossible in visible light, and the first detailed maps did not emerge until the arrival of the Magellan orbiter in 1991. Plans have been proposed for rovers or more missions. Venus is one of the four planets in the Solar System
29.
Uranus
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Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System, Uranus is similar in composition to Neptune, and both have different bulk chemical composition from that of the larger gas giants Jupiter and Saturn. For this reason, scientists often classify Uranus and Neptune as ice giants to distinguish them from the gas giants, the interior of Uranus is mainly composed of ices and rock. Uranus is the planet whose name is derived from a figure from Greek mythology. Like the other giant planets, Uranus has a system, a magnetosphere. The Uranian system has a unique configuration among those of the planets because its axis of rotation is tilted sideways and its north and south poles, therefore, lie where most other planets have their equators. In 1986, images from Voyager 2 showed Uranus as an almost featureless planet in visible light, observations from Earth have shown seasonal change and increased weather activity as Uranus approached its equinox in 2007. Wind speeds can reach 250 metres per second, like the classical planets, Uranus is visible to the naked eye, but it was never recognised as a planet by ancient observers because of its dimness and slow orbit. Uranus had been observed on many occasions before its recognition as a planet, possibly the earliest known observation was by Hipparchos, who in 128 BCE might have recorded it as a star for his star catalogue that was later incorporated into Ptolemys Almagest. The earliest definite sighting was in 1690 when John Flamsteed observed it at least six times, the French astronomer Pierre Lemonnier observed Uranus at least twelve times between 1750 and 1769, including on four consecutive nights. Sir William Herschel observed Uranus on March 13,1781 from the garden of his house at 19 New King Street in Bath, Somerset, England, Herschel engaged in a series of observations on the parallax of the fixed stars, using a telescope of his own design. Herschel recorded in his journal, In the quartile near ζ Tauri, either Nebulous star or perhaps a comet. On March 17 he noted, I looked for the Comet or Nebulous Star and found that it is a Comet, the sequel has shown that my surmises were well-founded, this proving to be the Comet we have lately observed. Herschel notified the Astronomer Royal, Nevil Maskelyne, of his discovery and received this flummoxed reply from him on April 23,1781, I dont know what to call it. It is as likely to be a planet moving in an orbit nearly circular to the sun as a Comet moving in a very eccentric ellipsis. I have not yet seen any coma or tail to it, although Herschel continued to describe his new object as a comet, other astronomers had already begun to suspect otherwise. Finnish-Swedish astronomer Anders Johan Lexell, working in Russia, was the first to compute the orbit of the new object and its nearly circular orbit led him to a conclusion that it was a planet rather than a comet. Berlin astronomer Johann Elert Bode described Herschels discovery as a star that can be deemed a hitherto unknown planet-like object circulating beyond the orbit of Saturn
30.
Sagittarius (constellation)
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Sagittarius is one of the constellations of the zodiac. It is one of the 48 constellations listed by the 2nd-century astronomer Ptolemy and its name is Latin for the archer, and its symbol is, a stylized arrow. Sagittarius is commonly represented as a centaur pulling-back a bow and it lies between Scorpius and Ophiuchus to the west and Capricornus to the east. The center of the Milky Way lies in the westernmost part of Sagittarius, as seen from the northern hemisphere, the constellations brighter stars form an easily recognizable asterism known as the Teapot. The stars δ Sgr, ε Sgr, ζ Sgr, and φ Sgr form the body of the pot, λ Sgr is the point of the lid, γ2 Sgr is the tip of the spout and these same stars originally formed the bow and arrow of Sagittarius. Marking the bottom of the teapots handle (or the shoulder area of the archer, are the bright star Zeta Sagittarii, named Ascella, and the fainter Tau Sagittarii. The constellation as a whole is often depicted as having the appearance of a stick-figure archer drawing its bow. Sagittarius famously points its arrow at the heart of Scorpius, represented by the reddish star Antares, following the direct line formed by Delta Sagittarii and Gamma2 Sagittarii leads nearly directly to Antares. Fittingly, Sagittarii is Alnasl, the Arabic word for arrowhead, and Delta Sagittarii is called Kaus Media, Kaus Media bisects Lambda Sagittarii and Epsilon Sagittarii, whose names Kaus Borealis and Kaus Australis refer to the northern and southern portions of the bow, respectively. α Sgr despite having the alpha appellation, is not the brightest star of the constellation, instead, the brightest star is Epsilon Sagittarii, at magnitude 1.85. Sigma Sagittarii is the constellations second-brightest star at magnitude 2.08, Nunki is a B2V star approximately 260 light years away. Nunki is a Babylonian name of origin, but thought to represent the sacred Babylonian city of Eridu on the Euphrates. Zeta Sagittarii, with apparent magnitude 2.61 of A2 spectra, is actually a star whose two components have magnitudes 3.3 and 3.5. Delta Sagittarii, is a K2 spectra star with magnitude 2.71 and only 85 light years from Earth. Eta Sagittarii is a star with component magnitudes of 3.18 and 10, while Pi Sagittarii is actually a triple system whose components have magnitudes 3.7,3.8. The Bayer designation Beta Sagittarii is shared by two systems, β¹ Sagittarii, with apparent magnitude 3.96, and β² Sagittarii. The two stars are separated by 0. 36° in the sky and are 378 light years from earth, Beta Sagittarii, located at a position associated with the forelegs of the centaur, has the traditional name Arkab, meaning achilles tendon. Nova Sagittarii 2015 No.2 was discovered on March 15,2015, by John Seach of Chatsworth Island, NSW and it lies near the center of the constellation
31.
Pluto
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Pluto is a dwarf planet in the Kuiper belt, a ring of bodies beyond Neptune. It was the first Kuiper belt object to be discovered, Pluto was discovered by Clyde Tombaugh in 1930 and was originally considered to be the ninth planet from the Sun. After 1992, its planethood was questioned following the discovery of objects of similar size in the Kuiper belt. In 2005, Eris, which is 27% more massive than Pluto, was discovered and this led the International Astronomical Union to define the term planet formally in 2006, during their 26th General Assembly. That definition excluded Pluto and reclassified it as a dwarf planet, Pluto is the largest and second-most-massive known dwarf planet in the Solar System and the ninth-largest and tenth-most-massive known object directly orbiting the Sun. It is the largest known trans-Neptunian object by volume but is less massive than Eris, like other Kuiper belt objects, Pluto is primarily made of ice and rock and is relatively small—about one-sixth the mass of the Moon and one-third its volume. It has an eccentric and inclined orbit during which it ranges from 30 to 49 astronomical units or AU from the Sun. This means that Pluto periodically comes closer to the Sun than Neptune, light from the Sun takes about 5.5 hours to reach Pluto at its average distance. Pluto has five moons, Charon, Styx, Nix, Kerberos. Pluto and Charon are sometimes considered a system because the barycenter of their orbits does not lie within either body. The IAU has not formalized a definition for binary dwarf planets, on July 14,2015, the New Horizons spacecraft became the first spacecraft to fly by Pluto. During its brief flyby, New Horizons made detailed measurements and observations of Pluto, on October 25,2016, at 05,48 pm ET, the last bit of data was received from New Horizons from its close encounter with Pluto on July 14,2015. In the 1840s, Urbain Le Verrier used Newtonian mechanics to predict the position of the then-undiscovered planet Neptune after analysing perturbations in the orbit of Uranus. Subsequent observations of Neptune in the late 19th century led astronomers to speculate that Uranuss orbit was being disturbed by another planet besides Neptune, by 1909, Lowell and William H. Pickering had suggested several possible celestial coordinates for such a planet. Lowell and his observatory conducted his search until his death in 1916, unknown to Lowell, his surveys had captured two faint images of Pluto on March 19 and April 7,1915, but they were not recognized for what they were. There are fourteen other known prediscovery observations, with the oldest made by the Yerkes Observatory on August 20,1909. Percivals widow, Constance Lowell, entered into a legal battle with the Lowell Observatory over her late husbands legacy. Tombaughs task was to image the night sky in pairs of photographs, then examine each pair
32.
Makemake
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Makemake is a dwarf planet and perhaps the largest Kuiper belt object in the classical population, with a diameter approximately two thirds that of Pluto. Makemake has one satellite, S/20151. Makemake’s extremely low temperature, about 30 K, means its surface is covered with methane, ethane. Makemake was discovered on March 31,2005, by a led by Michael E. Brown. Initially, it was known as 2005 FY9 and later given the minor-planet number 136472, Makemake was recognized as a dwarf planet by the International Astronomical Union in July 2008. Its name derives from Makemake in the mythology of the Rapa Nui people of Easter Island. Makemake was discovered on March 31,2005, by a team at the Palomar Observatory, led by Michael E. Brown, despite its relative brightness, Makemake was not discovered until well after many much fainter Kuiper belt objects. Most searches for minor planets are conducted relatively close to the ecliptic, besides Pluto, Makemake is the only other dwarf planet that was bright enough that Clyde Tombaugh could have detected it during his search for trans-Neptunian planets around 1930. At the time of Tombaughs survey, Makemake was only a few degrees from the ecliptic, near the border of Taurus and Auriga, at an apparent magnitude of 16.0. This position, however, was very near the Milky Way. Tombaugh continued searching for years after the discovery of Pluto. The provisional designation 2005 FY9 was given to Makemake when the discovery was made public, before that, the discovery team used the codename Easterbunny for the object, because of its discovery shortly after Easter. In July 2008, in accordance with IAU rules for classical Kuiper belt objects,2005 FY9 was given the name of a creator deity. The name of Makemake, the creator of humanity and god of fertility in the myths of the Rapa Nui, as of December 2015, Makemake is 52.4 AU from the Sun, almost as far from the Sun as it ever reaches on its orbit. Makemake follows a very similar to that of Haumea, highly inclined at 29°. Nevertheless, Makemakes orbit is farther from the Sun in terms of both the semi-major axis and perihelion. Its orbital period is nearly 310 years, more than Plutos 248 years, both Makemake and Haumea are currently far from the ecliptic—the angular distance is almost 29°. Makemake is approaching its 2033 aphelion, whereas Haumea passed its aphelion in early 1992, Makemake is a classical Kuiper belt object, which means its orbit lies far enough from Neptune to remain stable over the age of the Solar System
33.
Asteroid
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Asteroids are minor planets, especially those of the inner Solar System. The larger ones have also been called planetoids and these terms have historically been applied to any astronomical object orbiting the Sun that did not show the disc of a planet and was not observed to have the characteristics of an active comet. As minor planets in the outer Solar System were discovered and found to have volatile-based surfaces that resemble those of comets, in this article, the term asteroid refers to the minor planets of the inner Solar System including those co-orbital with Jupiter. There are millions of asteroids, many thought to be the remnants of planetesimals. The large majority of known asteroids orbit in the belt between the orbits of Mars and Jupiter, or are co-orbital with Jupiter. However, other orbital families exist with significant populations, including the near-Earth objects, individual asteroids are classified by their characteristic spectra, with the majority falling into three main groups, C-type, M-type, and S-type. These were named after and are identified with carbon-rich, metallic. The size of asteroids varies greatly, some reaching as much as 1000 km across, asteroids are differentiated from comets and meteoroids. In the case of comets, the difference is one of composition, while asteroids are composed of mineral and rock, comets are composed of dust. In addition, asteroids formed closer to the sun, preventing the development of the aforementioned cometary ice, the difference between asteroids and meteoroids is mainly one of size, meteoroids have a diameter of less than one meter, whereas asteroids have a diameter of greater than one meter. Finally, meteoroids can be composed of either cometary or asteroidal materials, only one asteroid,4 Vesta, which has a relatively reflective surface, is normally visible to the naked eye, and this only in very dark skies when it is favorably positioned. Rarely, small asteroids passing close to Earth may be visible to the eye for a short time. As of March 2016, the Minor Planet Center had data on more than 1.3 million objects in the inner and outer Solar System, the United Nations declared June 30 as International Asteroid Day to educate the public about asteroids. The date of International Asteroid Day commemorates the anniversary of the Tunguska asteroid impact over Siberia, the first asteroid to be discovered, Ceres, was found in 1801 by Giuseppe Piazzi, and was originally considered to be a new planet. In the early half of the nineteenth century, the terms asteroid. Asteroid discovery methods have improved over the past two centuries. This task required that hand-drawn sky charts be prepared for all stars in the band down to an agreed-upon limit of faintness. On subsequent nights, the sky would be charted again and any moving object would, hopefully, the expected motion of the missing planet was about 30 seconds of arc per hour, readily discernible by observers
34.
Minor planet
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A minor planet is an astronomical object in direct orbit around the Sun that is neither a planet nor exclusively classified as a comet. Minor planets can be dwarf planets, asteroids, trojans, centaurs, Kuiper belt objects, as of 2016, the orbits of 709,706 minor planets were archived at the Minor Planet Center,469,275 of which had received permanent numbers. The first minor planet to be discovered was Ceres in 1801, the term minor planet has been used since the 19th century to describe these objects. The term planetoid has also used, especially for larger objects such as those the International Astronomical Union has called dwarf planets since 2006. Historically, the asteroid, minor planet, and planetoid have been more or less synonymous. This terminology has become complicated by the discovery of numerous minor planets beyond the orbit of Jupiter. A Minor planet seen releasing gas may be classified as a comet. Before 2006, the IAU had officially used the term minor planet, during its 2006 meeting, the IAU reclassified minor planets and comets into dwarf planets and small Solar System bodies. Objects are called dwarf planets if their self-gravity is sufficient to achieve hydrostatic equilibrium, all other minor planets and comets are called small Solar System bodies. The IAU stated that the minor planet may still be used. However, for purposes of numbering and naming, the distinction between minor planet and comet is still used. Hundreds of thousands of planets have been discovered within the Solar System. The Minor Planet Center has documented over 167 million observations and 729,626 minor planets, of these,20,570 have official names. As of March 2017, the lowest-numbered unnamed minor planet is 1974 FV1, as of March 2017, the highest-numbered named minor planet is 458063 Gustavomuler. There are various broad minor-planet populations, Asteroids, traditionally, most have been bodies in the inner Solar System. Near-Earth asteroids, those whose orbits take them inside the orbit of Mars. Further subclassification of these, based on distance, is used, Apohele asteroids orbit inside of Earths perihelion distance. Aten asteroids, those that have semi-major axes of less than Earths, Apollo asteroids are those asteroids with a semimajor axis greater than Earths, while having a perihelion distance of 1.017 AU or less. Like Aten asteroids, Apollo asteroids are Earth-crossers, amor asteroids are those near-Earth asteroids that approach the orbit of Earth from beyond, but do not cross it
35.
Earth
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Earth, otherwise known as the World, or the Globe, is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets, according to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago. Earths gravity interacts with objects in space, especially the Sun. During one orbit around the Sun, Earth rotates about its axis over 365 times, thus, Earths axis of rotation is tilted, producing seasonal variations on the planets surface. The gravitational interaction between the Earth and Moon causes ocean tides, stabilizes the Earths orientation on its axis, Earths lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earths surface is covered with water, mostly by its oceans, the remaining 29% is land consisting of continents and islands that together have many lakes, rivers and other sources of water that contribute to the hydrosphere. The majority of Earths polar regions are covered in ice, including the Antarctic ice sheet, Earths interior remains active with a solid iron inner core, a liquid outer core that generates the Earths magnetic field, and a convecting mantle that drives plate tectonics. Within the first billion years of Earths history, life appeared in the oceans and began to affect the Earths atmosphere and surface, some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. Since then, the combination of Earths distance from the Sun, physical properties, in the history of the Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely, over 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humans have developed diverse societies and cultures, politically, the world has about 200 sovereign states, the modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most often spelled eorðe. It has cognates in every Germanic language, and their proto-Germanic root has been reconstructed as *erþō, originally, earth was written in lowercase, and from early Middle English, its definite sense as the globe was expressed as the earth. By early Modern English, many nouns were capitalized, and the became the Earth. More recently, the name is simply given as Earth. House styles now vary, Oxford spelling recognizes the lowercase form as the most common, another convention capitalizes Earth when appearing as a name but writes it in lowercase when preceded by the. It almost always appears in lowercase in colloquial expressions such as what on earth are you doing, the oldest material found in the Solar System is dated to 4. 5672±0.0006 billion years ago. By 4. 54±0.04 Gya the primordial Earth had formed, the formation and evolution of Solar System bodies occurred along with the Sun
36.
Telescope
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A telescope is an optical instrument that aids in the observation of remote objects by collecting electromagnetic radiation. The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s and they found use in both terrestrial applications and astronomy. Within a few decades, the telescope was invented, which used mirrors to collect. In the 20th century many new types of telescopes were invented, including radio telescopes in the 1930s, the word telescope now refers to a wide range of instruments capable of detecting different regions of the electromagnetic spectrum, and in some cases other types of detectors. The word telescope was coined in 1611 by the Greek mathematician Giovanni Demisiani for one of Galileo Galileis instruments presented at a banquet at the Accademia dei Lincei, in the Starry Messenger, Galileo had used the term perspicillum. The earliest recorded working telescopes were the telescopes that appeared in the Netherlands in 1608. Their development is credited to three individuals, Hans Lippershey and Zacharias Janssen, who were spectacle makers in Middelburg, Galileo heard about the Dutch telescope in June 1609, built his own within a month, and improved upon the design in the following year. Also in 1609, Thomas Harriot became the first person known to point a telescope skyward in order to make observations of a celestial object. The idea that the objective, or light-gathering element, could be a mirror instead of a lens was being investigated soon after the invention of the refracting telescope. The potential advantages of using parabolic mirrors—reduction of spherical aberration and no chromatic aberration—led to many proposed designs, in 1668, Isaac Newton built the first practical reflecting telescope, of a design which now bears his name, the Newtonian reflector. The invention of the lens in 1733 partially corrected color aberrations present in the simple lens and enabled the construction of shorter. The largest reflecting telescopes currently have objectives larger than 10 m, the 20th century also saw the development of telescopes that worked in a wide range of wavelengths from radio to gamma-rays. The first purpose built radio telescope went into operation in 1937, since then, a tremendous variety of complex astronomical instruments have been developed. The name telescope covers a range of instruments. Most detect electromagnetic radiation, but there are differences in how astronomers must go about collecting light in different frequency bands. The near-infrared can be collected much like light, however in the far-infrared and submillimetre range. For example, the James Clerk Maxwell Telescope observes from wavelengths from 3 μm to 2000 μm, on the other hand, the Spitzer Space Telescope, observing from about 3 μm to 180 μm uses a mirror. Also using reflecting optics, the Hubble Space Telescope with Wide Field Camera 3 can observe in the range from about 0.2 μm to 1.7 μm
37.
85 Io
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85 Io is a large, dark main-belt asteroid of the C spectral class. It is probably a primitive body composed of carbonates, like 70 Panopaea it orbits within the Eunomia asteroid family but it is not related to the shattered parent body. Io is a rotator, with its pole pointing towards one of ecliptic coordinates = or with a 10° uncertainty. This gives an axial tilt of about 125° or 115°, respectively and it was discovered by C. H. F. Peters on September 19,1865, and named after Io, a lover of Zeus in Greek mythology. An Ionian diameter of 178 kilometres was measured from an occultation of a star on December 10,1995, another asteroid occultation of Io occurred on March 12,2009, from the eastern USA, with the star 2UCAC35694429. Io is also the name of the satellite of Jupiter. With a two-digit number and a name,85 Io has the shortest designation of all minor planets
38.
201 Penelope
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201 Penelope is a large main belt asteroid that was discovered by Austrian astronomer Johann Palisa on August 7,1879 in Pola. The asteroid is named after Penelope, the wife of Odysseus in Homers The Odyssey, based upon the spectra of this object, it is classified as a M-type asteroid, indicating it may be metallic in composition. It may be the remnant of the core of a larger, near infrared absorption features indicate the presence of variable amounts of low-iron, low-calcium orthopyroxenes on the surface. Trace amounts of water is detected with a fraction of about 0. 13–0.15 wt%. It has a size of around 88 km. With a rotation period of 3.74 hours, it is the fastest rotating asteroid larger than 50 km in diameter
. Bibcode:1999astro.ph..4413C. doi:10.1086/308525.
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