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Motions Of The Earth
Earth has two types of motions namely rotation and revolution.Rotation is the movement of the earth on its axis.The movement of the earth around the sun in a fixed path or orbit is called Revolution.It takes 3651/4 days to revolve around the sun.
The axis of the earth which is an imaginary line makes an angle of 661/2 with its orbital plane.The plane formed by the orbit is known as the orbital plane.
The circle that divides the day from night on the globe is called the circle of illumination.
The earth takes about 24 hours to complete one rotation around its axis.The period of rotation is known as the earthday.This is the daily motion of the earth.
Since a large portion of the Northern Hemisphere gets light from the sun.It is summer in the regions north of the equator.The longest day and the shortest night at these places occur on 21st June.At this time in the Southern Hemisphere all these conditions are reversed.It is winter there. The nights are longer than the days. This position of the earth is called the Summer Solstice.
On 22nd December ,the Tropic of Capricorn receives direct rays of the sun as the South Pole tilts towards it.As the sun's rays fall vertically at the Topic of Capricorn a larger portion of the Southern hemisphere gets light.Therefore 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 Winter Solstice.
On 21st March and September 23 rd direct rays of the sun fall on the equator.At this position,neither of the poles is tilted towards the sun so the entire earth experience equal days and equal nights. This is called equinox.