Impact on hemispherical advent of seasons:

Earth revolves around sun in an elliptical orbit and throughout the orbit, it is inclined in the same direction i.e. 66 1/2o to the plane of orbit. This results in change of seasons on the earth due to change in the position of the earth around the sun.

On 21 st June, the Northern Hemisphere is tilted towards the sun. Since a large portion of the Northern Hemisphere is getting light from the sun, it is summer in the regions north of the equator. At this time in the Southern Hemisphere, all these conditions are reversed. It is winter season there. This position of the earth is called the Summer Solstice.

On 22nd December, the southern hemisphere is tilted towards the sun. Therefore, it is summer in the Southern Hemisphere with reverse conditions 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, neither of the poles is tilted towards the sun; so, the whole earth experiences equal days and equal nights. This is called Spring Equinox and Autumn Equinox respectively.

Impact on lengths of the day:

During the summer solstice, the North Pole is inclined towards the sun. The rays of the sun fall directly on the Tropic of Cancer and regions in the northern hemisphere receive more sunlight for longer time than southern hemisphere. This results in longer days and shorter nights in the northern hemisphere and the length of the day increases towards the northern pole. The places beyond the Arctic Circle experience continuous daylight for about six months.

The conditions are reversed during winter solstice with the South Pole inclined towards the Sun. The Southern Hemisphere will have longer days and shorter nights.

During equinox, 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.

Daylight Saving Time (DST):

It is the practice of advancing clocks forward one hour near the start of spring and are adjusted backward in autumn. During the summer months, the sun rises earlier and sets later and there are more hours of daylight. If clocks are set ahead the sun will rise and set later in the day as measured by those clocks. This provides more usable hours of daylight for activities that occur in the afternoon and evening. Daylight saving time can also be a means of conserving electrical and other forms of energy.

Daylight saving time begins in the northern hemisphere between March–April and ends between September–November. Daylight saving time begins in the southern hemisphere between September– November and ends between March–April.

Utility of DST in India:

For tropical and equatorial countries like India, day and night are almost of same length. Thus the practice of advancing clocks will not have much utility in tropical countries like India. Even if it is followed, the daylight time saved in the morning will be lost in the evening. Though some parts of north India receives more daylight during summer, following DST in some parts and not in others is not a feasible practice.