2.  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.

4. Mercury is the second smallest of the planets and is also the closest to
the sun. It completes its orbit in a much shorter span of time than the
other planets. As a result it takes only 88 earth days to go around the
sun.
However, it rotates very slowly, in about59 earth days. Surface
temperatures vary between -180oC to +430oC.

5. Venus is identical to the earth in size, so it is often called the ‘earth’s
twin’, but it is too hot to support any life. It has a suffocating atmosphere
of sulphuric clouds and acid rain. This makes it the hottest planet. Like
Mercury, it also has no moon. Venus takes 243 days to rotate and about
225 earth days to move around the sun. A day on Venus is, therefore
longer than a year ! Moreover, its rotation is ‘retrograde’, that is, in the
opposite direction to that of the earth’s. That is why the sun rises in the
west and sets in the east when we see it from Venus.

6. The Earth is the only known planet with suitable temperature, oxygen
and water which together make life possible. It takes 365 days and 6
hours to complete one round of the sun and moves on its axis once in 24
hours. It has one moon. The earth is the fifth largest planet in the solar
system. Unlike other planets which are rich in carbon dioxide, the
Earth’s atmosphere is rich in nitrogen and oxygen.The earth is
approximately150 million km away from the sun.

7. Mars is the ‘Red Planet’. It is so called because there is a rust like coating
on its surface soil that is often blown into great storms. Astronomers
thought that life was possible here, but the ‘Viking’ space probes that
visited it in 1976 proved it otherwise. It has two moons. The planet rotates
around in a little over 24 1/2 hours. Mars takes nearly twice as long as the
Earth to complete one revolution around the sun (687 days), in July 1997
NASA’s Pathfinder landed on Mars and began sending very clear picture
of the ‘Martian’ environment. As a result Americans plant on land human
beings on Mars before the year 2020 A.D. They now know that the Red
Planet has a thin carbon dioxide atmosphere with frozen icecap. The
southern cap consists of carbon dioxide, but the ice cap in the north is
made up of frozen water.

8. Jupiter is the largest planet – one and half times the size of all the planets
put together. It revolves around the sun once in nearly 12 years. It spins
faster than any planet, once in 9 hours and 55 minutes. It is made up of hot
liquid hydrogen, helium, methane and is enveloped by frosting clouds.
Jupiter can be distinguished from the other planets by its circular light and
dark bands and the satellites that circle around it. It has a spectacular
Great Red Spot, which is actually a big storm that has existed on its surface
for centuries.

9. Saturn takes over 29 and a half years to revolve around the sun. It turns
around on its axis just a little slower than Jupiter. It is the second largest
planet and is a ‘gas giant’. It has more than 18 moons. Thousands of rings
of dust and sparkling ice encircle the planet and make a pretty sight.
Jupiter,Saturn,Uranus and Neptune also have rings.

10. Uranus is the seventh planet from the Sun. It has the third-largest
planetary radius and fourth-largest planetary mass in the Solar
System. It is named after the ancient Greek deity of the
sky Uranus (Ancient Greek: Οὐρανός), the father of Cronus (Saturn)
and grandfather of Zeus (Jupiter). Though it is visible to the naked
eye like the five classical planets, it was never recognized as a planet
by ancient observers because of its dimness and slow
orbit. Sir William Herschel announced its discovery on March 13,
1781, expanding the known boundaries of the Solar System for the
first time in modern history. Uranus was also the first planet
discovered with a telescope.

11. Neptune Is The Eighth And Farthest Planet From The Sun In The Solar
System. It Is The Fourth-largest Planet By Diameter And The Third Largest
By Mass. Neptune Is 17 Times The Mass Of Earth And Is Somewhat More
Massive Than Its Near-twin Uranus, Which Is 15 Times The Mass Of Earth
But Not As Dense. On Average, Neptune Orbits The Sun At A Distance Of
30.1 Au, Approximately 30 Times The Earth–sun Distance. Named For
The Roman God Of The Sea, Its Astronomical Symbol Is ♆, A Stylized
Version Of The God Neptune's trident.

12.  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 Earth's Moon And A Third Its Volume.Charon,Eris and
ceres are newly grouped dwarf planets.

14.  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.

16.  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.

18.  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.