Chapter - Review:
- The phenomenon of day and night is because of the rotation of the earth. Had there been no rotation, one side of the earth would perpetually have night, and temperatures would have dropped in this half. The other half would forever have a day, and in this half, temperatures would have risen. In such cases, It wpould nort be possible to sustain life on earth.
- Earth takes 24 hours to complete one rotation and this is known as earth day.
- 23 hr 56 min 4 sec is the actual time taken to complete on rotation, but for convenience purposes, it is taken to be 24 hours.
- The movement of the earth on its own axis around the sun is termed a revolution.
- The earth moves around the sun in an elliptical - shaped orbit.
- It takes 365.25 days to complete one revolution. This is the time taken by the earth to go round an elliptical orbit with the sun at a focus.
- We consider 365 days as one year, and the rest one - fourth of a day is added up for every four years to give us one extra day. This day is added up to the fourth year, and the year has 366 days. This year is called a leap year. This day is added up to the month of february.
- In a leap year, february has 29 days instead of 28 days.
- Seasons change due to change in the position of the Earth around the sun.
- Because of the change in the position of earth, a year is divided into summer, winter, spring and autumn.
- Summer solstice begins on 21st June in the Northern Hemisphere.
- On this day, the Northern Hemisphere is tilted towards he sun.
- Sun rays fall on the Tropic of cancer.
- The North pole is inclined towards the sun and areas beyound the Arctic Circle experience continuous daylight for about six months.
- The longest day and shortest night occur on 21st June, the summer Solstice.
- The conditions in the Southern Hemisphere are reversed, and it is winter season there.
- Winter solstice occurs on the 22nd of December in the Northern Hemisphere.
- The Southern Hemisphere at this time is tilted towards the sun.
- The Sunrays fall on the Tropic of Capricorn in the Southern Hemisphere.
- The Southern Hemisphere has loger days during this period and shorter night.
- The conditions are reversed in the northern hemisphere.
- The direct rays of the sun fall on the equator on 21st March and 23rd September.
- The whole Earth experiences equal days and equal night because neither of the poles is tilted towards the sun.
- On 23rd September, it is autumn season in the Northern hemisphere and spring season in the Southern hemisphere.
- The opposite is the caes on 21st march when it is spring in the Northern hemisphere and autumn in the Southern hemisphere.
