ASTEROIDS
An asteroid is a very small heavenly body that revolves round the sun. It is also called a planetoid (minor planet).
Most of the asteroids are found in the wide gap between the orbits of Mars and Jupiter. The largest asteroid is Ceres which is about 1000 kilometers across. It was discovered on January l, 1801 A.D. It must be remembered that asteroids have very irregular surfaces and shapes. Also, they have unusual orbits to circle round the sun.
There are thousands of known asteroids. About 30,000 of them shine brightly at times to be photographed. Astronomers know about the orbits of about 4000 of them.
Gravity of Jupiter keeps constantly affecting the orbits of asteroids. It may lead to collisions and chain-collisions. As a result, still smaller asteroids may be formed. The closest recorded collision took place on March 22, 1989 A.D. Most of the asteroids are believed to have been formed when dust-specks circling the sun took the shape of small clumps. These clumps, then, collected together and grew in size.
METEORS
A meteor is a bright streak of light seen in the sky for a very short time. So, it is also called a shooting star or falling star because it looks like a star falling from the sky.
A meteor is indeed a chunk of metallic or rocky matter that enters the earth's atmosphere from space. This matter is called a meteoroid. Friction of the air makes it so hot that it glows and leaves a trail of hot glowing gases behind it.
Astronomers believe that about 200 million visible meteors enter the earth's air-coat every day. A meteor becomes visible when it is about 105 kilometers away from the surface of the earth. By the time it reaches between 50 to 80 kilometers from the earth, it has caught fire.
Meteors belong to the solar system of which our earth is a part. They move faster than the earth does. When they have entered the earth's atmosphere, their speed increases considerably.
Most of the meteors are the size of a sand-grain and burn for a few seconds only. But the trail of a meteor lasts a good few minutes.
The picture given in front shows a meteor approaching the surface of the earth.
