On September 22^nd or 23^rd in the Northern Hemisphere, night and day are nearly of the same length as the Sun crosses the Equator, moving southwards. And in the Southern Hemisphere on 20^th or 21^st March, the Sun crosses the Equator, moving northwards it is known as Autumn Equinox.

The sunrays at noon are the hottest in comparison to the sunrays of the morning and evening. This is because the rays of the Sun are almost vertical at noon. They fall over a small area and hence, give a greater amount of heat that means the heat received at per unit area increase. The rays of the Sun are slanting in the morning and in the evening. They spread over a wider area and hence, they cover larger area but give less amount of heat. That is why, it is hotter when the sunrays are vertical at a place.

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.

Dusk: It is that period of evening which has diffused light after the Sunset.
Dawn: It is that period of the morning which has diffused light just before the Sunrise.

Two effects of Earth's rotation are:
(i) Due to rotation of the Earth, there is regular occurrence of tides twice a day and their gradual westward progress.
(ii) It causes the formation of day and night

The differences between rotation and revolution of the Earth are as follows:

The important dates that receive direct sun rays on different parts of the Earth are as follows.
(i) 21st March Equator receives direct sun rays.
(ii) 21st June Northern hemisphere receives direct sun rays.
(iii) 23rd September Equator receives direct sun rays.
(iv) 22nd December Southern hemisphere receives direct sun rays.

The circle of illumination does not coincide with the axis of the Earth because of the inclination of the axis by 23 1/2°. The circle of illumination divides day from night and the Earth takes 24 hours to complete one rotation around its axis.

The Earth has two types of motions. one is revolution and other is rotation. Rotation is the movement of the Earth on its axis, while the movement of the Earth around the sun in an orbit (fixed path) is called revolution (second type of motion of the Earth).
The day and night, and season change on the Earth is caused by rotation and revolution respectively.

The comparison between axis and orbit is as follow:
Axis The axis of the Earth is an imaginary line which joins North Pole to South Pole and makes an angle of 66 1/2°. with its orbital plane.
Orbit The Earth moves around the sun in a path which is called orbit and it is an elliptical path.

On 21st June, the Northern hemisphere is tilted towards the sun. These areas receive more heat because sun rays fall directly on the tropic of Cancer. As the larger portion of Northern hemisphere gets light from the sun, it is summer in the Northern part of equator.

It is because the rays of the sun are slanting due to the Earth's inclined position and movement of the Earth. The Earth is spherical in shape, so only half of it gets light from the sun at a same time. The portion facing sun experiences day while other portion experiences night.

The movement of the Earth on its axis around the sun takes 365 days (one year) and 6 hours to revolve once around the sun. We ignore six hours for the sake of convenience and consider a year consisting of 365 days. Saved six hours are added to make one day (24 hours) over span of four years.
This surplus day is added to the month of February and in every fourth year, February is of 29 days in spite of 28 days.

If the Earth did not rotate, then the Earth would have extreme temperature conditions and life would have not been possible. The portion before the sun would have remained the same and continuously experienced day.
On the other hand, the portion of the Earth away from the sunlight would have experienced night continuously.
The portion with continuous day would have very high temperature and portion with continuous night would have very low temperature.

The North Pole remains inclined towards the sun for six months due to which places beyond the Arctic circle experience continuous daylight for about six months while South Pole remains away from the sun for six months and experiences night for same period. The same condition reverses for the next six months when South Pole inclines towards the sun and experiences day while North Pole experiences night