GENERAL DESCRIPTION
| The third planet from the sun is the largest of the four terrestrial planets. Its position relative to the sun is such that the overall surface temperature is neither too hot nor too cold for life to exist. In addition, its mass and gravity are of just the right size to provide a layer of gases, the atmosphere, which protect the living organisms from the harmful solar radiation. Earth has only one moon, which is the sixth largest moon in the Solar System. As perceived from Earth, the moon appears to go through a series of phases depending upon its reflection of light from the sun. When the moon is fully illuminated, it is said to be 'full'. When exactly half the face of the moon is illuminated, it is called 'a quarter moon'. As it becomes less visible, it is said to become a 'crescent moon'. |