The universe consists of planets,stars etc. Mercury, venus, earth, mars, jupiter, saturn, uranus, neptune, and pluto are the main planets that we have learnt. The sun is the only celestial body that emits light. With the help of a telescope we can observe other celestial bodies like uranus,neptune,comets,meteoroids,asteroids, galaxies,dwarf planets billions of stars and other gaseous objects.Mercury,Venus,Earth and Mars are called solid planets while jupiter,saturn,uranus and neptune are called gaseous planets.
Mercury is the second smallest of the planets and is also the closest tothe sun. It completes its orbit in a much shorter span of time than theother planets. As a result it takes only 88 earth days to go around thesun.However, it rotates very slowly, in about59 earth days. Surfacetemperatures vary between -180oC to +430oC.
Venus is identical to the earth in size, so it is often called the ‘earth’stwin’, but it is too hot to support any life. It has a suffocating atmosphereof sulphuric clouds and acid rain. This makes it the hottest planet. LikeMercury, it also has no moon. Venus takes 243 days to rotate and about225 earth days to move around the sun. A day on Venus is, thereforelonger than a year ! Moreover, its rotation is ‘retrograde’, that is, in theopposite direction to that of the earth’s. That is why the sun rises in thewest and sets in the east when we see it from Venus.
The Earth is the only known planet with suitable temperature, oxygenand water which together make life possible. It takes 365 days and 6hours to complete one round of the sun and moves on its axis once in 24hours. It has one moon. The earth is the fifth largest planet in the solarsystem. Unlike other planets which are rich in carbon dioxide, theEarth’s atmosphere is rich in nitrogen and oxygen.The earth isapproximately150 million km away from the sun.
Mars is the ‘Red Planet’. It is so called because there is a rust like coatingon its surface soil that is often blown into great storms. Astronomersthought that life was possible here, but the ‘Viking’ space probes thatvisited it in 1976 proved it otherwise. It has two moons. The planet rotatesaround in a little over 24 1/2 hours. Mars takes nearly twice as long as theEarth to complete one revolution around the sun (687 days), in July 1997NASA’s Pathfinder landed on Mars and began sending very clear pictureof the ‘Martian’ environment. As a result Americans plant on land humanbeings on Mars before the year 2020 A.D. They now know that the RedPlanet has a thin carbon dioxide atmosphere with frozen icecap. Thesouthern cap consists of carbon dioxide, but the ice cap in the north ismade up of frozen water.
Jupiter is the largest planet – one and half times the size of all the planetsput together. It revolves around the sun once in nearly 12 years. It spinsfaster than any planet, once in 9 hours and 55 minutes. It is made up of hotliquid hydrogen, helium, methane and is enveloped by frosting clouds.Jupiter can be distinguished from the other planets by its circular light anddark bands and the satellites that circle around it. It has a spectacularGreat Red Spot, which is actually a big storm that has existed on its surfacefor centuries.
Saturn takes over 29 and a half years to revolve around the sun. It turnsaround on its axis just a little slower than Jupiter. It is the second largestplanet and is a ‘gas giant’. It has more than 18 moons. Thousands of ringsof dust and sparkling ice encircle the planet and make a pretty sight.Jupiter,Saturn,Uranus and Neptune also have rings.
Uranus is the seventh planet from the Sun. It has the third-largestplanetary radius and fourth-largest planetary mass in the SolarSystem. It is named after the ancient Greek deity of thesky Uranus (Ancient Greek: Οὐρανός), the father of Cronus (Saturn)and grandfather of Zeus (Jupiter). Though it is visible to the nakedeye like the five classical planets, it was never recognized as a planetby ancient observers because of its dimness and sloworbit. Sir William Herschel announced its discovery on March 13,1781, expanding the known boundaries of the Solar System for thefirst time in modern history. Uranus was also the first planetdiscovered with a telescope.
Neptune Is The Eighth And Farthest Planet From The Sun In The SolarSystem. It Is The Fourth-largest Planet By Diameter And The Third LargestBy Mass. Neptune Is 17 Times The Mass Of Earth And Is Somewhat MoreMassive Than Its Near-twin Uranus, Which Is 15 Times The Mass Of EarthBut Not As Dense. On Average, Neptune Orbits The Sun At A Distance Of30.1 Au, Approximately 30 Times The Earth–sun Distance. Named ForThe Roman God Of The Sea, Its Astronomical Symbol Is ♆, A StylizedVersion Of The God Neptunes trident.
Pluto, Formal Designation 134340 Pluto, Is The Second-most-massive Known Dwarf Planet In The Solar System (After Eris) And The Tenth- most-massive Body Observed Directly Orbiting The Sun. Originally Classified As The Ninth Planet From The Sun, Pluto Was Recategorized As A dwarf Planet And Plutoid Due To The Discovery That It Is Only One Of Several Large Bodies Within The Kuiper Belt. Like Other Members Of The Kuiper Belt, Pluto Is Composed Primarily Of Rock And Ice And Is Relatively Small: Approximately A Sixth The Mass Of The Earths Moon And A Third Its Volume.Charon,Eris and ceres are newly grouped dwarf planets.
The Moon is the only natural satellite of the Earth, and the fifth largest satellite in the Solar System. It is the largest natural satellite of a planet in the Solar System relative to the size of its primary, having a quarter the diameter of Earth and 1⁄81its mass. The Moon is the second densest satellite after Io, a satellite of Jupiter.
The Milky Way is the galaxy in which Earth is contained. This name derives from its appearance as a dim "milky" glowing band arching across the night sky, in which the naked eye cannot distinguish individual stars.
A comet is an icy small Solar System body (SSSB) that, when close enough to the Sun, displays a visible coma(a thin, fuzzy, temporary atmosphere) and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. Comets have been observed since ancient times and have traditionally been considered bad omens.The tail of the comet is seen in the opposite direction of the sun.