WHAT ARE PLANETS?

The word planet has been derived from the Greek word "planetes" which means wanderer. Planets were first discovered to be different from the stars by Greek astronomers in ancient times. They look much like stars in the night-sky but two facts make them differ from the stars.

1. Planets shine steadily as they are dark solid bodies and have no light of their own. They get light from the sun and shine by virtue of this light.

Stars, on the other hand, appear to be twinkling just as the flame of a candle flickers in light wind, This twinkle is caused by the moving air of the atmosphere.

2. Planets move in relation to the stars. Ancient Greek scholars also first noted this movement.

The planets differ greatly in size and also in distance from the sun. As for weight, they together weigh less than a hundredth of the sun's weight.

Jupiter, Saturn, Uranus and Neptune are called major planets while Mercury, Venus, Earth and Mars are called terrestrial planets.

Pluto has not yet been placed in any of the two categories as little is known about it.

Astronomers do not believe that there are any more planets beyond Pluto. But they believe that most of the other stars in the universe have planets revolving around them.

Most of the planets have smaller non-light-emitting bodies revolving round them. These smaller bodies are called their satellites or moons. Just like the planets, these moons are lit by sunlight and shine partly at a time.

Our moon is the only satellite of our earth. It is lit with sunlight and reflects it back into the space. Most of the heat of the sunlight is absorbed by its surface. As a result, the moonshine is cool and soothing. It is, in fact, true in the case of all the moons of various planets.