Seasonal changes on earth-पृथ्वी पर मौसमी परिवर्तन

A season is a division of the year marked by changes in weather, ecology, and amount of daylight. Seasons result from Earth's orbit around the Sun and Earth's axial tilt relative to the ecliptic plane.

 In temperate and polar regions, the seasons are marked by changes in the intensity of sunlight that reaches the Earth's surface, variations of which may cause animals to undergo hibernation or to migrate, and plants to be dormant.

Equinox-21 March-

21 March – Sun rays fall  on equator. This is known as Equinox. Day and night are equal.

On Northern Hemisphere, there is spring season and in Southern hemisphere, there is autumn season.

 Spring is declining winter and increasing summer. Whereas in Autumnis reverse to it.

The line ofSolstice

A solstice is an event occurring when the Sun appears to reach its most northerly or southerly excursion relative to the celestial equator on the celestial sphere.

 Two solstices occur annually, around June 21 and December 21.

The seasons of the year are determined by reference to both the solstices and the equinoxes.

The line of apsides

The line of apsides, connecting the two points, is the major axis of the orbit. The point nearest the focus is the pericentre, or periapsis, and that farthest from it is the apocentre, or apoapsis.

Apoapsis (plural apoapsides) (astronomyThe point of a body's elliptical orbit about the system's centre of mass where the distance between the body and the centre of mass is at its maximum.

21 June – This position is known as solstice. Sun rays falls perpendicular on Tropic of Cancer. Because of that on Northern Hemisphere, there is summer season and on southern hemisphere, there is winter season. It is longest, hottest day and shortest night in N- hemisphere. On S – hemisphere, there is shortest day, coldest day and longest night.

Equinox-21 September-

23^rd September – Sun rays fall perpendicular on equator. Thus the day and night will be equal. This position is known as Equinox. On N- Hemisphere, there is Autumn and on S-Hemisphere, spring season is found.

21 December –Sun rays falls perpendicular on Tropic on Capricorn. This positionis also known as solstice. Because of that at Northern-Hemisphere, there is winter season and on Southern-Hemisphere, there is summer season. On N-H, coldest day, coldest night, smallest day and longest night. On S-H, hottest day, longest day and shortest night.Lava.

Thus Christmas comes in summer season in following countries which are at or close to Tropic of Capricorn:-Newzealand, Australia, Brazil, Africa.

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