The Planet Earth and The Solar System

The Planet Earth and The Solar System -

We can see countless glittering tiny objects in the sky at night. Most of these appear twinkling. They are stars. The other glittering objects which do not seem to be twinkling may be planets. During the day, we see the Sun, which is also a star

All objects in the sky, which appear similar to us, are the heavenly bodies. The sun, the stars, the moon, the planets and the other objects are the heavenly or celestial bodies. Even our earth, on which we live, is a celestial body.

The stars and the planets, which we see in the sky, are very small part of the vast "Space", which is limitless. There are billions of celestial bodies spread over the vast space. They are very, very far away from us. Hence, we cannot see all of them. The vast limitless space which includes all celestial bodies us called Universe. 

GALAXIES

Though there are billions of celestial bodies spread in the vast universe, they are not uniformly distributed in the space. The countless stars in the space form huge clusters. One cluster may contain billions of stars. All the stars in a cluster are held together by mutual gravitational force. Such a huge cluster if billions of stars, along with the giant collection of gas and dust, is called a Galaxy.

Our earth, along with the other planets, forms the Solar System. The Solar System is located in the outwards spiral (Orion Arm) of the Milky Way Galaxy (Akash Ganga). Most likely, there are billions of the solar systems in our galaxy and billions of galaxies in the universe.  As we know, there are different types of celestial bodies in the universe.

STARS

Stars are self-luminous heavenly bodies. The are made up of hot gases. They generate heat and light and radiate it in the space. The number of stars is countless. We cannot see all of them at a time. It has been said that, at one time, we can see not more than 6,000 stars. Though, stars are very huge bodies, they look very small as they are very away from earth. The distance between celestial bodies is usually measured in a unit know as light year. 

Some stars are so far away that the light radiated by them reaches us in millions of years. The nearest star to the earth, other than the sun, is the 'Proxima Centauri'. It is about 4.246 light year away from us. 

CONSTELLATIONS

If you observe the stars in clear night sky, they appear to form different shapes and patterns and move from west to east. The formations may resemble animals are called Constellations. 

Ursa Major, also called the Great Bears, is a constellation if several stars. It appears in the northern sky. In India, the seven stars called Saptarishi Mandal, is a part of Great Bear. There are several other formation of stars, which have been given names by astronomers. The two brightest stars at the head of the Saptarishi Mandal, called Pointers, points towards the stationary star called Pole Star or Dhruv Tara in the northern sky. Pole Star lies above the North Pole. It always indicates the North direction.

Indians and Greeks have been studying the shapes and patterns of stars since ancient times. In modern times, the space scientist and astronomers use powerful and large-sized telescopes to study the celestial bodies.

THE SOLAR SYSTEM 

The sun and its companion celestial bodies constitute the Solar System. The eight planets, their companion satellites, asteroids, meteors and comets are the members of the solar system. They all revolve around the sun on their fixed paths called Orbits.

The Evolution of the Solar System -

A question sometimes arises in our minds, how were the sun and its companions born? Some scientist believe that a giant cloud of gases and dust, called the Nebula, appeared moving in the space about 4.6 billions of years ago. It cooled and gained very fast rotation. The eight balls of gases of different sizes were separated from the Nebula. The remaining central mass of the Nebula changed into a star known as the Sun. The other eight balls changed into planets.

It is believed that the satellites were formed when small balls of gaseous disks with dust separated from the central mass and were attracted to their companion planets. Due to gravity, they began to revolve around their planets.

THE SUN  

The Sun is a star. A star does not have a solid surface, but is a ball of gases held together by its own gravity. It generates heat and light and radiates them into space. The Sun does not have any rings. It is the centre of the solar system. Life would not be possible on earth without the sun's intense energy.

The Sun is a very huge mass, much bigger than all its companions put together. It is about 1.3 million times bigger than our earth.

Due to the sun's huge size, all members of the solar system are held by its gravitational pull and they revolve round it in their respective orbits.

Though, the distance between the earth and the sun is about 150 million kilometers, it is the nearest star to the earth as compared to other stars. The rays of the sun reach the earth's surface in about eight minutes.

THE PLANETS

Planets are the heavenly bodies which receive light and heat from the Sun. They do not have their own light. The total number of planets in the solar system are eight. In the order of their distance from the sun, they are- Mercury, Venus, Earth, Mars, Jupiter, Saturn,Uranus and Neptune. 

The first four planets in order to their distance from the Sun are- Mercury, Venus, Earth and Mars. They are called the terrestrial planets because the have solid, rocky surface. Two of the outer planets, Jupiter and Saturn, are known as gas giants whereas the more distant, Uranus and Neptune, are called ice giants.

Mercury has a thin atmosphere. The days are very hot, but at night temperature drops hundreds of degree below freezing point. It is the smallest planet in our solar system. Venus is the hottest planet due to its volcanic activities and thick atmosphere. It spins backwards. Earth is the only planet which supports life due to its optimum amount of heat, light and oxygen. Mars, known as the Red Planet, is a cold desert. Its atmosphere is too thin for liquid water to exist for long on the surface. Jupiter, Saturn, Uranus and Neptune have rings. The rings around Jupiter are very faint and hence, cannot be seen by naked eyes. The atmosphere of Jupiter, Saturn and Uranus is mostly made up of hydrogen and helium. Other than these gases, Uranus has methane, which gives blue tint to it. Neptune is similar in composition to Uranus, composed primarily of hydrogen and helium along with traces of hydrocarbons and nitrogen. It also contains a higher proportion of ammonia and methane.

-Keva