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Why do we have different seasons? How earth’s rotation and revolution effect temperature
As the earth is continuously rotating and revolving, the portion of the earth that is exposed to sun changes. Earth’s axis makes an angle of 62.5 degrees with its orbital plane – the plane formed by earth’s orbit.
Effects of Earth’s 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.
Image taken from NCERT Class 6
- 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. The areas near the poles receive less heat as the rays of the sun are slanting.
- Continuous daylight in The North Pole – The North Pole is inclined towards the sun and the places beyond the Arctic Circle experience continuous daylight for about six months.
- Since a large portion of the Northern Hemisphere is getting 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 season there. The nights are longer than the days.
- This position of the earth is called the Summer Solstice.
- Winter Solstice
- 22nd december, the sun rays fall straight on the Tropic of Capricon
- The South Pole is tilted towards the Sun
- 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
- When the length of the day and the length of the night is exactly same
- On 21st March and 23rd September
- Direct rays of 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.
- On 23rd September, it is autumn season in the Northern Hemisphere and spring season in the Southern Hemisphere. The opposite is the case on 21st March.
Effects of Earth’s Rotation
- Circle of Illumination
- The circle that divides day from night on the globe is called the Circle of Illumination.
- This circle does not coincide with the axis
- Rotation – Earthday
- The Earth rotates once around its axis in 24 hrs, this daily motion of the earth is called as earthday