Revaluation of the seasons by motion of earth is the crucial reason for the major change in seasons.
It divides every year into various seasons, making it the primary reason.The season change happens not due to the distance but due to the earth’s axis.
Rotation of Earth
- Earth rotates along its axis from west to east.
- It takes approximately 24 hrs tocomplete on rotation.
- Days and nights occurdue to rotation of the earth.
- The circle that divides the day from night on the globe is called the circleof illumination.
- Earth rotates on a tilted axis. Earth’s rotational axis makes an angle of 23.5° with the normal i.e. it makes an angleof 66.5° with the orbital plane.
- Orbital plane is the plane of earth’s orbitaround the Sun.
- On 21st June, the northern hemisphere is tilted towards thesun.
- 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 heatas the rays of the sun are slanting.
- The sun inclines the North Pole, causing places beyond the Arctic Circle to 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, all these conditions are reversed in the southern hemisphere. It is winter season 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 towardsit.
- As the sun’s rays fall vertically at the Tropic of Capricorn (23½° s), a larger portion of the southern hemisphere getslight.
- 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.
- On 21st March and September 23rd, direct rays of the sun fall on the equator.
- At this position, the Sun does not tilt either of the poles, resulting in the whole Earth experiencing equal days and equal nights.
- This is called an equinox.
- On 23rd September, it is autumn season (vernal) [season after summer and before the beginning of winter] in the northern hemisphere
- spring season [season after winter and before the beginning of summer] in the southern hemisphere.
- The opposite is the case on 21st March, when it is spring in the northern hemisphere and autumn in the southern hemisphere.
- Thus, you find that there are days and nights and changes in the seasons because of the rotation and revolution of the earth respectively.
- The Earth’s second motion around the Sun in its orbit is called revolution.
- It takes 365¼ days (one year) to revolve around the sun.
- Every year, we add six saved hours to make one day (24 hours) over a span of four years. We add this surplus day to the month of February.
- Thus every fourth year, February is of 29 days instead of 28 days.
- Such a year with 366 days is called a leap year.
Seasonality by Motion of Earth,Seasonality by Motion of Earth
Also read : Laurentian Climate