Rotation And Revolution Of Earth
Imagine a line passing through the center of Earth that goes through both the North Pole and the South Pole. This imaginary line is called an axis. Earth spins around its axis, just as a top spins around its spindle. This spinning movement is called Earth’s rotation. At the same time that the Earth spins on its axis, it also orbits, or revolves around the Sun. This movement is called revolution.
Rotation of Earth
- Rotation is the movement of the earth on its axis.
- Earth rotates along its axis from west to east.
- It takes approximately 24 hrs to complete one rotation.
- Days and nights occur due to the rotation of the earth.
- The circle that divides the day from night on the globe is called the circle of illumination.
- The Earth rotates on a tilted axis making an angle of 23.5° with the normal i.e. it makes an angle of 66.5° with the ecliptic plane (ecliptic plane is the plane of Earth’s orbit around the sun).
Effect of rotation on Earth
- The duration of the day and night is not equal at all places on the earth because of the inclined axis. The length of days varies with respect to different seasons in different latitude.
- It affects the movement of water in the oceans. The tides are originated due to the rotation of the earth.
- The speed of rotation also affects the general circulation of the atmosphere. The winds and ocean currents are deflected to the right in the Northern Hemisphere and to the left in the southern hemisphere.
Revolution of Earth
- The movement of the earth around the sun in a fixed path or orbit is called Revolution.
- It takes 365¼ days (one year) to revolve around the sun. We consider a year as consisting of 365 days only and ignore six hours for the sake of convenience.
- Every year 6 hours is saved which is added in the month of February in every fourth year. Thus every fourth year, February is of 29 days instead of 28 days. Such a year with 366 days is called a leap year.
- The earth revolves around the sun in an elliptical orbit.
Effects of Revolution on Earth
- Seasonal Changes: The amount of heat that a place receives on earth depends on the angle the sun’s rays with the earth. The more vertical the sun’s rays, the hotter will be the place. Whereas the same amount of heat is spread over a larger area, in the case of the oblique rays.
- During Summer Solstice i.e. on 21st June, the Northern Hemisphere is tilted towards the sun. The rays of the sun fall directly on the Tropic of Cancer which makes these areas receive more heat. The areas near the poles receive less heat as the rays of the sun are slanting. During this time days, are of the longest and nights are the shortest. While in Southern hemisphere completely opposite happen.
- On 22nd December, the Tropic of Capricorn receives direct rays from the sun as the South Pole tilts towards it. So, it is summer in the Southern Hemisphere with longer days and shorter nights. The reverse happens in the Northern Hemisphere. This position of the earth is called the Winter Solstice.
- On 21st March and 23rd September, direct rays from the sun fall on the equator. At this position, neither of the poles is tilted towards the sun; so, the whole earth experiences equal days and equal nights. This is called an equinox.
Also refer:
- Free General Studies Notes
- Important Facts About World Geography.
- To download the pdf of top 50 science questions from previous year UPSC prelims, click here.
