1.
Lunar phase
–
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
2.
Astronomy
–
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
3.
Computer-generated imagery
–
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
4.
Moon
–
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
5.
Star
–
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
6.
Antares
–
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
7.
Pleiades
–
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
8.
Binary star
–
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
9.
Quasar
–
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
10.
Solar eclipse
–
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
11.
Rhea (moon)
–
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
12.
Saturn
–
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
Definitions from Wiktionary
Media from Wikimedia Commons
News from Wikinews
Quotations from Wikiquote
Texts from Wikisource
Textbooks from Wikibooks
Learning resources from Wikiversity
