Earth’s Motions
👉 The earth has two types of motions, namely rotation, and revolution.
ROTATION:
👉 Rotation is the movement of the earth on its axis.
👉 The earth takes about 24 hours to complete one rotation around its axis.
👉 The period of rotation is known as the earth’s day.
👉 This is the daily motion of the earth.
👉 The axis of the earth which is an imaginary line, makes an angle of 66.5° with its ORBITAL PLANE.n of the earth.
👉 The earth receives light from the sun. Due to the spherical shape of the earth, only half of it gets light from the sun at a time. The portion facing the sun experiences day while the other half away from the sun experiences night.
👉 The circle that divides the day from night on the globe is called the CIRCLE OF ILLUMINATION.
REVOLUTION:
👉 The movement of the earth around the sun in a fixed path or orbit is called Revolution.
👉 It takes 365 days 6 hours to revolve around the sun.
👉 We consider a year as consisting of 365 days only and ignore 6 hours for the sake of convenience.
👉 Six hours saved every year are added to make one day over a span of 4 years. This surplus day is added to the month of February. That’s why every fourth year, February is 29 days instead of 28 days. Such a year with 366 days is called a LEAP YEAR.
👉 The earth moves around the sun in an elliptical orbit.
👉 Due to the change in the position of the earth around the sun seasons changes.
👉 A year is usually divided into summer, winter, spring, and autumn seasons.
Summer Solstice:
👉In the Northern Hemisphere the longest day and the shortest night occur on 21st June. In the Southern Hemisphere, the shortest day and the longest night occur on this day. This position of the earth is known as the summer solstice
👉On 21st June, the Northern Hemisphere is tilted towards the sun. The rays of the sun fall directly on the Tropic of Cancer. As a result, these areas receive more heat and it is summer in the regions north of the equator.
👉In the Southern Hemisphere all these conditions are reversed. It is winter seasons there.
Winter 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 Tropic of Capricorn (23½° S), 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 the Winter Solstice.
Equinox:
👉On 21st March and September 23rd, direct rays of the sun fall on the equator, and the whole earth experiences equal days and equal nights. This is called an equinox.
👉 On 23rd September, it is autumn season in the Northern Hemisphere and spring season in the Southern Hemisphere.
👉 On 21st March, it is spring in the Northern Hemisphere and autumn in the Southern Hemisphere.
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