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UNIVERSEThe universe is commonly defined as the totality of everything that exists, including allmatter and energy, the planets, stars, galaxies, and the contents of intergalactic space.Definitions and usage vary and similar terms include the cosmos, the world and nature.Scientific observation of earlier stages in the development of the universe, which can beseen at great distances, suggests that the universe has been governed by the samephysical laws and constants throughout most of its extent and history. There are variousmultiverse theories, in which physicists have suggested that our universe might be oneamong many universes that likewise exist.The word universe derives from the Old French word Univers, which in turn derives fromthe Latin word universum.The Latin word was used by Cicero and later Latin authors inmany of the same senses as the modern English word is used.The Latin word derives fromthe poetic contraction Unvorsum — first used by Lucretius in Book IV (line 262) of his Dererum natura (On the Nature of Things) — which connects un, uni (the combining form ofunus, or "one") with vorsum, versum (a noun made from the perfect passive participle ofvertere, meaning "something rotated, rolled, changed").
The night sky In day time only sun is visible in the sky. As soon as the sun sets sky appear full of twinklingstars. The twinkling takes place due to atmosphere of the Earth on clear night. There arebillions of stars in the universe it. which are not uniformly distributed. These occur in the formof huge bunches or clusters. Such a group of stars is a single galaxy.The Sun ,the Earth and other planets and all the stars that we see in the sky belong to a galaxycalled Milky way. It is also called akash ganga. It assumed that there are some 1011 galaxies inthe universe and each galaxy contains 1011 stars in it.The fact that the sky is not completely dark at night can be easily observed. Were the sky (inthe absence of moon and city lights) absolutely dark, one would not be able to see thesilhouette of an object against the sky. MILKY WAY
stars A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth.. Other stars are visible from Earth during the night, when they are not obscured byatmospheric phenomena, appearing as a multitude of fixed luminous points because of theirimmense distance. Historically, the most prominent stars on the celestial sphere weregrouped together into constellations and asterisms, and the brightest stars gained propernames. Extensive catalogues of stars have been assembled by astronomers, which providestandardized star designations. For at least a portion of its life, a star shines due tothermonuclear fusion of hydrogen in its core releasing energy that traverses the stars interiorand then radiates into outer space.
Almost all naturally occurring elements heavier than helium were created by stars, eithervia stellar nucleosynthesis during their lifetimes or by supernovaNucleosynthesis when stars explode. Astronomers can determine the mass, age, chemicalcomposition and many other properties of a star by observing its spectrum, luminosity andmotion through space. The total mass of a star is the principal determinant in its evolutionand eventual fate. Other characteristics of a star are determined by its evolutionaryhistory, including diameter, rotation, movement and temperature. A plot of thetemperature of many stars against their luminosities, known as a Hertz sprung-Russelldiagram (H–R diagram), allows the age and evolutionary state of a star to be determined.The colour of star depends upon its temperature. Most of stars are so far away from Earththat light from them takes millions of years to reach us. The distance of stars is thereforeexpressed in terms of light years. One light year is the distance travelled byLight in one year(the speed of light isAbout 3,00,000 kilometer per secondTherefore , 1 light Year= Distancetravelled by light in One year.
constellationsIn modern astronomy, a constellation is an internationally defined area of the celestialsphere. These areas are grouped around asterisms, patterns formed by prominent starswithin apparent proximity to one another on Earths night sky.There are 88 standard constellations recognized by the International Astronomical Union(IAU) since 1922. The majority of these go back to the 48 constellations defined by Ptolemyin his Almagest (2nd century). The remaining ones were defined in the 17th and 18thcentury; the most recent ones are found on the southern sky, defined in Coelum australestelliferum by Nicolas Louis de Lacaille (1763).There are also numerous historical constellations not recognized by the IAU, orconstellations recognized in regional traditions of astronomy or astrology, such as Chinese,Hindu or AustralianAboriginal. We can easily identify someconstellation with Naked eyes. SomeImportant constellations are-
URSA MAJOR Ursa Major (Latin: "Larger Bear"), also known as the Great Bear, is a constellation visiblethroughout the year in most of the northern hemisphere. It can best be seen in April. It isdominated by the widely recognized asterism known as the Big Dipper or Plough, which is auseful pointer toward north, and which has mythological significance in numerous worldcultures. URSA MINORUrsa Minor (Latin: "Smaller Bear", contrasting with Ursa Major), also known as the LittleBear, is a constellation in the northern sky. Like the Great Bear, the tail of the Little Bearmay also be seen as the handle of a ladle, hence the name Little Dipper. It was one of the48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88modern constellations
ORIONOrion, sometimes subtitled The Hunter, is a prominent constellation located on thecelestial equator and visible throughout the world. It is one of the most conspicuous, andmost recognizable constellations in the night sky. Its name refers to Orion, a hunter in Greekmythology. SCORPIOScorpio, sometimes known as Scorpio, is one of the constellations of the zodiac. Its name isLatin for scorpion, and its symbol is (Unicode ♏). It lies between Libra to the west andSagittarius to the east. It is a large constellation located in the southern hemisphere near thecenter of the Milky Way.
SOLAR SYSTEM We are here
The planets mercuryMercury is the innermost of the eight planets in the Solar System. It is also the smallest, andits orbit has the highest eccentricity of the eight. It orbits the Sun once in about 88 Earthdays, completing three rotations about its axis for every two orbits. Mercury has thesmallest axial tilt of the Solar System planets. The perihelion of Mercurys orbit precessesaround the Sun at an excess of 43 arc seconds per century beyond what is predicted byNewtonian mechanics, a phenomenon that was explained in the 20th century by AlbertEinsteins General Theory of Relativity.Mercury, being an inferior planet, appears asa morning star and an evening star, but is much more difficult to see than the other inferior planet, Venus. At its brightest, Mercury is technically a very bright object when viewedfrom Earth, but it is not easily seen in practice because of its proximity in the sky to the Sun.
VenusVenus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet isnamed after Venus, the Roman goddess of love and beauty. After the Moon, it is thebrightest natural object in the night sky, reaching an apparent magnitude of −4.6, brightenough to cast shadows. Because Venus is an inferior planet from Earth, it never appearsto venture far from the Sun: its elongation reaches a maximum of 47.8°. Venus reaches itsmaximum brightness shortly before sunrise or shortly after sunset, for which reason it hasbeen known as the Morning Star or Evening Star.Venus is classified as a terrestrial planet and it is sometimes called Earths "sister planet"owing to their similar size, gravity, and bulk composition. Venus is covered with an opaquelayer of highly reflective clouds of sulfuric acid, preventing its surface from being seenfrom space in visible light. Venus has the densest atmosphere of all the terrestrial planetsin the Solar System, consisting of mostly carbon dioxide. The atmospheric pressure at the planets surface is 92 times that of the Earth. Venus has no carbon cycle to lock carbon back into rocks and surface features, nor does it seem to have anyorganic life to absorb it in biomass. Venus is believed to have previously possessed oceans, but theseevaporated as the temperature rose owing to therunaway greenhouse effect..
earthEarth (or the Earth) is the third planet from the Sun, and the densest and fifth-largest of theeight planets in the Solar System. It is also the largest of the Solar Systems four terrestrialplanets. It is sometimes referred to as the world, the Blue Planet, or by its Latin name, Terra.Earth formed approximately 4.54 billion years ago by accretion from the solar nebula, andlife appeared on its surface within one billion years. The planet is home to millions ofspecies, including humans. Earths biosphere has significantly altered the atmosphere andother abiotic conditions on the planet, enabling the proliferation of aerobic organisms aswell as the formation of the ozone layer which, together with Earths magnetic field, blocksharmful solar radiation, permitting life on land. The physical properties of the Earth, as wellas its geological history and orbit, have allowed life to persist. The planet is expected tocontinue supporting life for another 500 million to 2.3 billion years.Earths crust is divided into several rigid segments, or tectonic plates, that migrate acrossthe surface over periods of many millions of years. About 71% of the surface is covered bysalt water oceans, with the remainder consisting of continents and islands which togetherhave many lakes and other sources of water that contribute to the hydrosphere. Earthspoles are mostly covered with solid ice (Antarctic ice sheet) or sea ice (Arctic ice cap). The planets interior remains active, with a thick layer of relatively solid mantle, a liquid outer core that generates a magnetic field, and a solid iron inner core.
marsMars is the fourth planet from the Sun in the Solar System. Named after the Roman god ofwar, Mars, it is often described as the "Red Planet" as the iron oxide prevalent on its surfacegives it a reddish appearance. Mars is a terrestrial planet with a thin atmosphere, havingsurface features reminiscent both of the impact craters of the Moon and the volcanoes,valleys, deserts, and polar ice caps of Earth. The rotational period and seasonal cycles ofMars are likewise similar to those of Earth, as is the tilt that produces the seasons. Mars isthe site of Olympus Mons, the highest known mountain within the Solar System, and ofValles Marineris, the largest canyon. The smooth Borealis basin in the northern hemispherecovers 40% of the planet and may be a giant impact feature.Until the first successful flyby of Mars occurred in 1965, by Mariner 4, many speculatedabout the presence of liquid water on the planets surface. This was based on observedperiodic variations in light and dark patches, particularly in the polar latitudes, whichappeared to be seas and continents; long, dark striations were interpreted by some asirrigation channels for liquid water. These straight line features were later explained asoptical illusions, though geological evidence gathered by unmanned missions suggest that Mars once had large-scale water coverage on its surface. In 2005, radar data revealed the presence of large quantities of water ice at the poles, and at mid-latitudes. The Mars rover Spirit sampledchemical compounds containing water molecules in March 2007. The Phoenix lander directly sampled water ice in shallow Martian soil on July 31, 2008.
JupiterJupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is agas giant with mass one-thousandth that of the Sun but is two and a half times the mass ofall the other planets in our Solar System combined. Jupiter is classified as a gas giant alongwith Saturn, Uranus and Neptune. Together, these four planets are sometimes referred to asthe Jovian or outer planets.The planet was known by astronomers of ancient times, and was associated with themythology and religious beliefs of many cultures. The Romans named the planet after theRoman god Jupiter. When viewed from Earth, Jupiter can reach an apparent magnitude of−2.94, making it on average the third-brightest object in the night sky after the Moon andVenus. (Mars can briefly match Jupiters brightness at certain points in its orbit.)Jupiter is primarily composed of hydrogen with a quarter of its mass being helium; it mayalso have a rocky core of heavier elements. Because of its rapid rotation, Jupiters shape isthat of an oblate spheroid (it possesses a slight but noticeable bulge around the equator).The outer atmosphere is visibly segregated into several bands at different latitudes,resulting in turbulence and storms along their interacting boundaries.A prominent result is the Great Red Spot, a giant storm that is knownto have existed since at least the 17th century when it was first seen by telescope. Surrounding the planet is a faint planetary ring systemand a powerful magnetosphere.
SaturnSaturn is the sixth planet from the Sun and the second largest planet in the Solar System,after Jupiter. Named after the Roman god Saturn, its astronomical symbol (♄) representsthe gods sickle. Saturn is a gas giant with an average radius about nine times that of Earth.While only 1/8 the average density of Earth, with its larger volume Saturn is just over 95times more massive than Earth.Saturns interior is probably composed of a core of iron, nickel and rock (silicon and oxygencompounds), surrounded by a deep layer of metallic hydrogen, an intermediate layer ofliquid hydrogen and liquid helium and an outer gaseous layer. Electrical current within themetallic hydrogen layer is thought to give rise to Saturns planetary magnetic field, which isslightly weaker than Earths and around one-twentieth the strength of Jupiters. The outeratmosphere is generally bland and lacking in contrast, although long-lived features canappear. Wind speeds on Saturn can reach 1,800 km/h.Saturn has a ring system that consists of nine continuous main rings and threediscontinuous arcs, composed mostly of ice particles with a smaller amount of rocky debris and dust. Sixty-two known moons orbit the planet; fifty-three are officially named. This does notinclude the hundreds of “moonlets" within the rings. Titan, Saturns largest and the Solar Systems second largest moon, is larger than the planet Mercury and is the only moon in the Solar System to retain a substantial atmosphere.
UranusUranus is the seventh planet from the Sun. It has the third-largest planetary radius andfourth-largest planetary mass in the Solar System. It is named after the ancient Greek deityof the sky Uranus (Ancient Greek: Οὐρανός), the father of Cronus (Saturn) and grandfatherof Zeus (Jupiter). Though it is visible to the naked eye like the five classical planets, it wasnever recognized as a planet by ancient observers because of its dimness and slow orbit. SirWilliam Herschel announced its discovery on March 13, 1781, expanding the knownboundaries of the Solar System for the first time in modern history. Uranus was also the firstplanet discovered with a telescope.Uranus is similar in composition to Neptune, and both are of different chemical compositionthan the larger gas giants, Jupiter and Saturn. Astronomers sometimes place them in aseparate category called "ice giants". Uranuss atmosphere, while similar to Jupiter andSaturns in its primary composition of hydrogen and helium, contains more "ices" such aswater, ammonia and methane, along with traces of hydrocarbons. It is the coldest planetaryatmosphere in the Solar System, with a minimum temperature of 49 K (−224 °C). It has a complex, layered cloud structure, with water thought to make up the lowest clouds, and methanethought to make up the uppermost layer of clouds. Incontrast, the interior of Uranus is mainly composed ofices and rock.
NeptuneNeptune is the eighth and farthest planet from the Sun in the Solar System. Named for theRoman god of the sea, it is the fourth-largest planet by diameter and the third largest bymass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twinUranus, which is 15 times the mass of Earth but not as dense. On average, Neptune orbitsthe Sun at a distance of 30.1 AU, approximately 30 times the Earth–Sun distance. Itsastronomical symbol is ♆, a stylized version of the god Neptunes trident.Neptune was the first planet found by mathematical prediction rather than by empiricalobservation. Unexpected changes in the orbit of Uranus led Alexis Bouvard to deduce thatits orbit was subject to gravitational perturbation by an unknown planet. Neptune wassubsequently observed on September 23, 1846 by Johann Galle within a degree of theposition predicted by Urbain Le Verrier, and its largest moon, Triton, was discovered shortlythereafter, though none of the planets remaining 12 moons were located telescopicallyuntil the 20th century. Neptune has been visited by only one spacecraft, Voyager 2, whichflew by the planet on August 25, 1989.Neptune is similar in composition to Uranus, and both have compositions which differ fromthose of the larger gas giants, Jupiter and Saturn. Neptunes atmosphere, while similar toJupiters and Saturns in that it is composed primarily of hydrogen and helium, along withtraces of hydrocarbons and possibly nitrogen, contains a higher proportion of "ices" such aswater, ammonia and methane. Astronomers sometimes categorize Uranus and Neptune as"ice giants" in order to emphasize these distinctions.