Page 111 - SST Class 06

and other bodies in the solar system. The Sun is The Planets
also the source of all energy in the solar system. A planet is described as a heavenly body whose
Our earth gets a very small fraction of its heat place among the stars is not fixed. The word
and light, yet it is the source of all energy and life ‘planet’ is derived from the Greek word ‘planetai’
on the earth. meaning ‘wanderer’. They actually wander in

SOLAR SYSTEM REDEFINED space following a regular path while going round
The Solar system has now only 8 planets. The the Sun. There are eight planets in the solar
International Astronomical Union (IAU) has system and the earth is one of them. These
drawn new rules for classification of celestial planets in order of their distance from the Sun
bodies. These celestial bodies will be grouped are Mercury, Venus, Earth, Mars, Jupiter, Saturn,
under three categories : Uranus and Neptune.
(a) Planets, Mercury : This is the closest planet to the Sun. It
is the smallest planet and is made of rock. It is so
(b) Dwarf Planets
close to the Sun that it only takes 88 days for it to
(c) Small Solar System Bodies.
complete its orbit and is much hotter than the
The new rules state that a planet must be “a
Earth.
celestial body that is in orbit around the Sun, has
Venus : Venus is the next planet from the Sun
sufficient mass for its self-gravity to overcome
after Mercury. It is also made of rock. Like the
rigid body forces so that it assumes a nearly
Earth, Venus has an atmosphere (air) around it,
round shape and has cleared the nighbourhood
but it is a lot thicker than the Earth and Venus is
around its orbit.” Pluto does not qualify to be a
permanently covered in clouds. Venus is the
planet under these new rules. Its oblong orbit
hottest planet and has an average temperature of
overlaps with neptune. In the first category of
460°C. It is about the same size as the Earth. It
Planets are Mercury, Venus, Earth, Mars, Jupiter,
takes 225 days to travel around the Sun.
Saturn, Uranus and Neptune. In the second
cateory of Dwarf Planets are Pluto and many Earth : This is where we live! The Earth is made
other planetoids. In the third category of Smaller of rock and is the only planet where water is
Solar System Bodies are included numerous liquid. The other planets are either too hot or too
asteroids, comets and other natural satelliters. cold. The Earth takes 365 days to travel around
the Sun.
DO YOU KNOW?
Mars : Mars is a little smaller than the Earth, but
The word ‘Sun’ is derived from the Latin word ‘sol’
a lot further out. It used to have an atmosphere
which itself has come from a Latin hymn ‘Sob’. In fact,
like Earth and Venus, but it doesn’t have very
sol is a variant of ‘sob’. The Vedic people in India also
much anymore. Mars is reddish in colour and is
used to worship the Sun as a deity and there are
sometimes called ‘The Red Planet’. Mars takes
references of its association with the spring season.
687 days to complete its orbit of the Sun and the
Similarly, there are other words in English which have
average temperature is (–63°C).
originated from other languages especially Latin and
Greek. For example, the word ‘geography’ (‘Geo’ Jupiter : Jupiter is the largest planet in the Solar
meaning ‘earth’ and ‘graphia’ meaning ‘description’) System. You could fit 1,321 Earths inside Jupiter.
means ‘earth description’. Geographers, therefore, It is made of gas and is one of the four ‘gas
study the physical features and othe details including giants’. Jupiter has 66 moons; one of them,
human action concerning the earth. Ganymede, is bigger than Mercury. Jupiter is five

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