# Competitive Exams: Motions of the Earth

The earth spins like a top on its axis, completing one rotation every 24 hours. This period is called a day. More precisely, it is a day-and-night. The earth is a non-luminous sphere, emitting no light of its own. That part of the earth's surface which is towards the sun at any time is lit up, while the remaining part, on the other side of the globe, is dark. That is what gives us day and night. As a result of the axial rotation of the earth, every part of the surface of the globe moves from light into darkness and from darkness into light. We have day and night following each other in turn, once every 24 hours. The earth rotates from west to east. That is why the. Sun, the moon and the stars appear to us to be moving in the opposite direction, i.e.. from east to west, every day.

## Rotation

The daily axial rotation of the earth causes.

1. Formation of the day and the night

2. Difference in Longitude and Time

3. Deflection of winds and currents

4. Occurrence of Tides twice a day.

## Change of Seasons

The earth, while rotating about its axis once every 24 hours, revolves round the sun in a vast elliptical orbit (path), keeping an average distance of some million kilometers from that luminary. One such revolution takes about 365 − 114 days. We call this period a year. For the sake of convenience, our ordinary year contains 365 days, and to make up for the difference, every fourth year (called a Leap Year) is reckoned to contain 366 days. On June 21, the sun shines vertically at the Tropic of Cancer; so it is summer in the Northern Hemisphere and winter in the Southern Hemisphere. On the other hand on December 22, it is the Tropic of Capricorn that receives the rays of the sun vertically, with the result that it is summer in the Southern Hemisphere and winter in the Northern Hemisphere. On March 21 and September 23, the sun is vertical at the equator and both the North and the South Poles are similarly situated with respect to the sun.