Question

How many days in a year do we have in an equinox, i.e. the duration of day and night are the same?
A) Two days
B) Four days
C) Five days
D) None of the above

Answer 1

Hint:
The earth has two types of motions which are called rotation and revolution. Rotation is the movement of the earth on its axis, whereas, Revolution is the movement of the earth around the sun in a fixed path or orbit.

Complete Answer:
The Northern Hemisphere on 21st June is tilted towards the sun. The rays of the sun fall directly on the Tropic of Cancer, thus, these areas receive more heat. As the rays of the sun are slanting, the areas near the poles receive less heat. For about six months, the places beyond the Arctic Circle experience continuous daylight since the North Pole is inclined towards the sun. It is thus summer in the regions north of the equator since a large portion of the Northern Hemisphere is getting light from the sun. On 21st June, the longest day and the shortest night occur at these places. At this time, the opposite of all these conditions happens in the Southern Hemisphere. It is winter season there and the nights are longer than the days. Thus, this position of the earth is called the Summer Solstice.
The Tropic of Capricorn receives direct rays of the sun on 22nd December as the South Pole tilts towards it. A larger portion of the Southern Hemisphere gets light as the sun’s rays fall directly at the Tropic of Capricorn. Therefore, in the Southern Hemisphere, it is summer with longer days and shorter nights. The opposite happens in the Northern Hemisphere. This position of the earth is called the Winter Solstice.
Direct rays of the sun fall on the equator on 21st March and 23rd September. Neither of the poles is tilted towards the sun at this position. So, equal days and equal nights are experienced by the whole earth. This position of the earth is known as an equinox.

Thus, option (A) is correct.

Note:
It is autumn season in the Northern Hemisphere on 23rd September and in the Southern Hemisphere it is the spring season. The reverse is the case on 21st March when it is spring in the Northern Hemisphere and autumn in the Southern Hemisphere.