3. About Planets
Planets are the large celestial bodies which revolve
around the sun in closed elliptical paths called
orbits. The planets shine because they reflect the
light of the sun which falls on them.The easiest
way to distinguish planets from the stars in the
night sky is that the stars twinkle at night but the
planets do not twinkle at night.The planets move
around the sun from west to east, so the relative
positions of the planets in the night sky keep
changing day by day. The planets are very small as
compared to the sun or other stars.
4. There are eight planets in the solar system -
1. Mercury
2. Venus
3. Earth
4. Mars
5. Jupiter
6. Saturn
7. Uranus
8. Neptune
5.
6. Inner Planets
Mercury,Venus,Earth and Mars are
inner planets. They are made of rocks
and have metallic cores. They are
comparatively small and dense bodies
having solid surfaces like our Earth.
Earth is the biggest of the four inner
planets
7. Outer planets
Jupiter, Saturn, Uranus and Neptune are called
outer planets.The first four outer planets are very
giant. They are made of hydrogen and helium gases
and not of rock and metal.
All the planets revolve around the sun and also
rotate on their axis. Some important facts and
figures about eight planets of the solar system are
given on the next slide.
8. Some important facts about planets
Name of Diameter Distance Time taken to turn no.of
Planet of planet from sun once on its axis moons
Mercury 4880km 58*106 58 days None
Venus 12100 km 108*106 225 days None
Earth 12760km 150*106 356 1/4 days 1
Mars 6780km 228*106 687 days 2
Jupiter 142800km 778*106 11 ¾ years 28
Saturn 120000km 1427*106 29 ½ years 30
Uranus 50800km 2870*106 84 years 21
Neptune 48600km 4504*106 165 years 8
9. Mercury
Mercury is the first planet from the earth.During
day time the surface of the mercury heats up to
430° but during night the temperature falls up to -
180° c due to lack of atmosphere. Mercury has a
rocky surface which is covered with
craters.Mercury is sometimes visible from earth,just
after sunrise or sunset. When mercury is visible just
before sunrise in the morning ,it is called “Morning
star” and when it is visible just after sunset, then it
is called “Evening star”.It can be seen as morning
star in the eastern sky in the month September and
October or as evening star in the western sky in the
month March and April .
10. Planet mercury show phases like moon. This is due to the
fact that the mercury lies in the orbit of the earth. So, as
mercury revolves around the sun, its sunlit surface is visible
in varying amounts from the earth this produces phases of
mercury. Many features of the mercury and Earth’s moon
are as follows:
1] Mercury and moon both are nearly of the same size and
mass.
2] Mercury and moon both have no atmosphere.
3] Mercury and moon both have rocky surface covered with
craters.
Mercury and moon both show phases when viewed from
the earth.
12. Venus
Venus is the second planet from the earth Venus is slightly
smaller than the earth.Venus is a rocky planet. The planet
Venus has a dense atmosphere which consists almost
entirely of carbon dioxide gas.The cloudy atmosphere of
Venus is an excellent reflector of sun light. The planet
Venus is the brightest object in the night sky(except the
moon).Being quite near to the sun , the planet Venus is
very hot .The planet Venus also gets heated excessively by
the trapping of the sun’s heat rays by carbon dioxide gas
present in its atmosphere which is also called green house
effect The maximum temperature on the planet is 480°c.
13. The planet Venus can be seen as a morning star
in the eastern sky or as a evening star in the
western sky The venues shows phases like
moon. This is due to the fact that the Venus lies
inside the earth’s orbit. So, as Venus revolves
around the sun,its sun-lit surface is presented to
the Earth in varying amounts. This produces the
phases of the Venus.Life cannot exist on the
planet Venus because it is extremely hot,it has
no water and there is no sufficient oxygen in its
atmosphere. Mercury and Venus are only two
planets which have no satellites or moons
revolving around the sun.
16. Earth
Earth is the third planet from the earth.When
viewed from the outer space,the earth appears
to be a blue and green ball due to the reflection
of sunlight from water and land on its surface
.The earth has an atmosphere contains gases like
nitrogen,oxygen,carbon dioxide, noble gases
,water vapor and some ozone .
18. The earth rotates on its axis.It rotates on
an imaginary axis which phases which
through its north and south pole. The
average temperature of the surface of the
earth is 15°c The earth has one natural
satellite called moon. The two major
factors which factors which are responsible
for the existence of life on the planet earth
are :size of the earth and distance of the
earth from the sun.
19. The motions of the earth
Rotation
The earth rotates or spin on an imaginary axis
which phases through its north and south
poles.The earth completes one rotation on its
axis in 24 hours which we call one day. This
causes day and night.The earth rotates on its
axis from east to west.The axis of rotation of
earth is slightly tilted with respect to the
plane of its orbit around the sun.
20. The rotation of the earth
causes Day and Night.
An important consequence of the rotation of the earth on
its axis is that it causes day and night on the earth. As the
earth rotates on its axis, first one half of the Earth is
turned around towards the sun. This part of earth receives
sunlight and has day on it. The part of earth which is
turned away from the sun does not receive any sunlight, it
remains dark and has night.Almost every 12 hours, a day
changes into night, and a night changes into day.The
change in the length of a day and night is, however,
caused by the tilt of Earth’s axis.
23. The Motion of the Earth Around
the Sun Causes Seasons
An important consequence of the revolution of the
Earth around the sun is that it causes seasons on
the earth such as summer, winter, spring and
autumn. Two factors are responsible for causing
different seasons on the Earth.These are:
1. Motions of the earth around the sun once every
year.
2. Tilt of the Earth’s axis to the plane of its orbit
around the sun.
24.
25. In The Northern hemisphere:
1)It is winter when the earth is closer to the sun.
2)It is summer when the earth is farther from the sun.
In the Southern hemisphere:
1)It is summer when the earth is closer to the sun.
2)It is winter when the earth is farther from the sun.
Earth has its own satellite (moon)The different views
of the moon as seen from the earth are called phases
of the moon.
26. Mars
Mars is the fourth planet from the sun.Mars is also
called the Red planet because its surface appears
red.The red color of Mars is caused by the presence
of hydrated iron oxide compound on its soil.
Of all of the planets, Mars is most like the
Earth.Mars is a rocky planet. Mars has a thin
atmosphere as compared to the Earth. The thin
atmosphere of mars contains mainly carbon dioxide
with small amounts of nitrogen, oxygen, noble
gases and water vapour.
27. Since the planet Mars is very far off from the Sun,
so it is quite cold planet. The surface temperature
on Mars varies from a minimum of, -87°c to a
maximum of 17°c. It has no water. The
atmosphere of mars is so thin that it allows the
deadly ultra violet rays of the sun to reach its
surface.Though no evidence of the existence of
any form of life on mars has been found so far but
investigations are still going on.Mars has two
natural satellites called ‘phobos’ and ‘Deimos’.
29. Jupiter
Jupiter is the fifth planet from the earth.Jupiter is the
biggest planet of the solar system.The diameter of
Jupiter is 11 times the diameter of the Earth and mass
is about 318 times that of the Earth.Because of its very
big size, Jupiter can be seen easily in the night
sky.Jupiter is made mainly of hydrogen and helium
gases. Jupiter has a very deep atmosphere . The
atmosphere of the Jupiter consists of helium, hydrogen,
methane and ammonia.The surface of the Jupiter is
mainly made of liquid hydrogen.
30. Jupiter is the first of the gas type planets.
Below the surface, increasing pressure changes
this liquid this liquid hydrogen to solid
state.Jupiter appears to be the brightest object
in the night sky. Jupiter’s bright appearance is
due to the fact that is it has a thick, cloudy
atmosphere which reflects most of the sunlight
falling on it.Jupiter is a very cold planet, its
surface temperature being,-180°c. Jupiter has
28 satellites .It has also some faint rings around
it.
32. Saturn
Saturn is the sixth planet from the sun.Saturn is somewhat
smaller in size and mass than Jupiter.Saturn is the second
biggest planet in the solar system.The distance of Saturn is
almost double that of Jupiter The chemical composition of
Saturn is very similar to that of Jupiter.Thus, Saturn is
made up mainly of hydrogen and helium gases.The
atmosphere of Saturn consists of hydrogen, helium,
methane and ammonia gases.Saturn has no solid
surface.The surface of Saturn is liquid hydrogen.Below the
surface is frozen hydrogen.The most distinguish feature of
Saturn is the system of colorful rings which surround it.
33. Three distinct sets of rings of Saturn are visible from
earth. Saturn is the only planet with a system of
well-developed rings encircling it.The rings of
Saturn are made up of tiny particles, all orbiting the
Saturn like miniature satellites The rings of Saturn
cannot be seen with naked eyes, they can be
observed only with the help of telescope.The
presence of a well-developed system of rings around
Saturn makes it unique in the solar system.Rings
have now been discovered around other planets –
Jupiter, Uranus and Neptune
35. Saturn is the most beautiful of all the planets.
Being far off from the sun, Saturn is an extremely
cold planet.The surface temperature on Saturn is,
-180° C. So, no life can exist on Saturn. Saturn
has the maximum number of satellites or moons of
all the planets in the solar system.Saturn has 30
satellites.
the biggest and brightest satellite of Saturn is
called Titan. Titan is bigger than the planet
mercury.
36. Uranus
Uranus is the seventh planet from the sun.Uranus was
the first planet to have been discovered with the help of
a telescope.Uranus was discovered with the William
Herschel in the year 1781.Though the diameter of
Uranus is almost four times that of the Earth, it
appears as a small disc through a telescope. This is
because Uranus is very, very far off from the Earth.The
distance of Uranus from the sun is almost double that
of the Saturn.After Jupiter and Saturn, Uranus is the
third biggest planet in the solar system.
37. After Jupiter and Saturn, Uranus is the third
biggest planet in the solar system.
Uranus is made up of mainly of hydrogen and
helium.It is surrounded by a thick atmosphere of
hydrogen, helium and methane. Uranus is an
extremely cold planet, its surface temperature
being,-190°C. It is also surrounded by an
atmosphere of poisonous gases.Due to these
reasons, no life can exist on the planet
Uranus.The planet Uranus has 21 satellites or
moons. It has also some rings around it.
40. Neptune
Neptune is the eighth planet from the sun.It lies beyond
the Uranus. Neptune is the second planet which is
discovered with the help of telescope.Neptune was the
first planet to be discovered as a result of predictions.
Neptune was discovered in 1846 as a result of the effect
of its gravitational pull on Uranus. The astronomers
noticed that the planet Uranus was not moving in its
orbit around the sun exactly as expected. The Uranus
had a slightly,irregular orbit as if ,something, was
pulling it out of its orbit due to its gravitational force.
42. In order to explain the deviation of Uranus from its normal
orbit , as an astronomer Le Verrier predicated the existence
of another planet beyond Uranus in June 1846. He thought
that this distant planet was disturbing the orbit of Uranus
due to its gravitational force. By making mathematical
calculations,Le Verrier even predicated the mass and size of
the unknown planet correctly.Le Verrier asked the
astronomers all over the world to search for the new planet
with their telescope .Johann Galle discovered this planet in
September1846.It was named Neptune.It was Newton's
Law of gravitation which formed the basis of Le Verrier’s
calculations which led to the discovery of planet Neptune.
43. The planet Neptune can be seen easily as a tiny
blue-green speck even by using the most powerful
telescope on the Earth.
Neptune is about the same size and mass as
Uranus.It is the last of the large planets. Neptune
is mainly made up of liquid and frozen hydrogen
and helium gases. The temperature of the surface
of Neptune is,-200C. No life can exist on the
planet Neptune. Neptune has 8 satellites.It has
also rings around it.
44. Signs of Zodiac
Although Earth moves around the sun, but it
appears from the earth that the sun moves around
the Earth against the background of stars.The 12
constellations through which the sun passes during
the course of a year are known as the signs of
Zodiac.The sun appears in different constellation
during different parts of the year.The names of 12
zodiacal signs are given below.The Indian name for
zodiacal sings are given in the next slide.
