Geography 6. The Earth in the Solar System
Celestial bodies are any astronomical bodies outside the earth’s atmosphere such as earth, moon, and sun.
Stars are celestial bodies made up of gas; emitting their own heat and light. Sun is a star.
Constellations are the various patterns formed by various group of stars. Eg: Ursa Major or Big Bear, Small Bear or Saptrishi, it’s a group of seven stars that forms a part of the large Ursa Major Constellation.
The North Star indicates the north direction. It’s also called the Pole Star. It always remains in the same position in the sky.
Planets are the celestial bodies that don’t have
their own heat and light. They’re lit by the light of stars. Eg: Earth.
The word ‘planet’ comes from the Greek word “Planetai” which means ‘wanderers’.
The Solar System
The sun, eight planets, satellites and some other celestial bodies known as asteroids and meteoroids form the solar system.
The sun
is in the centre of the solar system. It’s huge and made up of extremely hot
gases. It provides the pulling force that binds the solar system. The sun is
the ultimate source of heat and light for the solar system. But that tremendous
heat isn’t felt so much by us because despite being our nearest star, it’s far
away from us. The sun is about 150 million km away from the earth.
Jupiter, Saturn and Uranus have rings around
them. These are belts of small debris.
These rings may be seen from the earth with
the help of powerful telescopes.
Orbits are the fixed path along which all the
planets move around the sun.
Venus is considered as ‘Earth’s-twin’ because its size and shape are very much
similar to that of the earth.
According to the International Astronomical
Union, which sets definitions for planetary science, a dwarf planet is a
celestial body that:
·
Orbits the sun.
·
Has enough mass to assume a nearly round
shape.
·
Hasn’t cleared the neighbourhood around its
orbit.
·
Isn’t a moon.
Pluto was considered to be a planet till August,
2003.
Ceres, 2003 UB313 are other examples.
The Earth is the 3rd nearest and 5th
largest planet in the solar system.
It’s slightly flattened at the poles. That’s
why; its shape is described as a Geoid. Geoid means an earth-like shape.
Earth is only planet favourable to life.
Earth’s called a Blue Planet because
from outer space it appears blue due to 2/3 of its surface covered with water.
Light travels at the speed of about 300,000 km/s. Yet, even with this speed, the light of the sun takes about 8 minutes to reach the earth.
A Satellite is a celestial body that moves around the
planets in the same way as the planets move around the sun.
A Human-made
Satellite is an artificial body. It’s designed by
scientists to gather information about the universe or for communication. It’s
carried by a rocket and placed in the orbit around the earth.
The Moon
Our earth has only one satellite, that is,
the moon. Its diameter is only 1/4th of the earth.
The moon moves around the earth in about 27.3
days. It takes exactly the same time to complete one spin. As a result, only
one side of the moon is visible to us on the earth.
The moon doesn’t have conditions favourable
for life. It has neither water nor air. It has mountains, plains and
depressions on its surface. These cast shadows on the moon’s surface.
Neil Armstrong was the first man to step on
the surface of the moon on 21 July 1969.
Asteroids are the tiny bodies that move around the sun
in addition to stars, planets and satellites. They’re found between the orbits
of Mars and Jupiter.
Scientists are of the view that asteroids are
parts of a planet which exploded many years back.
Meteoroids are the small pieces of rocks derived mostly
from asteroids which move around the sun. Sometimes these meteoroids come near
the earth and tend to drop upon it. During this process due to air friction
they get heated up and burn. It causes a flash of light. Sometimes, a meteor
without being completely burnt falls on the earth and creates a hollow.
Milky Way galaxy is a cluster of millions of stars
that appears like a white glowing path across the sky on a clear starry night.
In ancient India, it was imagined to be a river of light flowing in the sky. Thus, it was named Akash Ganga.
A galaxy is a huge system of billions of stars, and clouds of dust and gases. There are millions of such galaxies that make the Universe.
Moon Cycle
At a full moon, the earth, moon,
and sun are in approximate alignment, just as the new moon, but the moon is on
the opposite side of the earth, so the entire sunlit part of the moon is facing
us. The shadowed portion is entirely hidden from view.
The first quarter and third quarter moons (both often called a half moon), happen when the moon is at a 90 degree angle w.r.t. the earth and sun. So we’re seeing exactly half of the moon illuminated and half in shadow.
Crescent refers to the phases where the moon is less than half
illuminated. Gibbous refers to phases where the moon
is more than half illuminated.
Waxing essentially means growing or expanding in illumination.
Waning means shrinking or decreasing in illumination.
Full moon night / Poornima can be seen once in a month’s time and a fort night later it’s a New moon night / Amavasya.
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