Q. Variations in the length of daytime and nighttime from season to season are due to

• The earth’s rotation on its axis
• The earth’s revolution round the sun in an elliptical manner
• Latitudinal position of the place
• Revolution of the earth on a titled axis

Answer: (d) Revolution of the earth on a titled axis

Notes:

• The number of hours of daylight, i.e. day length, on any particular day of the year differs from place to place.
• If we take two locations on the Earth, Earth’s equator and North Pole, then we can find that equator only receives about 12 hours of light each day, whereas the north pole receives 24 hours of daylight for a few months in the summer and then total darkness in the winter months.
• As we know, day and night are the consequence of the earth’s rotation on its axis. But, the axis is tilted 23.5 degrees.
• Due to this reason, during the earth’s revolution around the sun, polar regions spend long periods pointed towards the sun in the summers and long periods pointed away from the sun during winters.
• Days of constant darkness or light occurs at latitudes greater than 66.5 degrees, the regions above the Arctic and the Antarctic.
• The summer solstice or the longest day of the year in the Northern Hemisphere is the day when earth’s north pole is tilting 23.5 degrees towards the sun.
• Similarly, the winter solstice, or the shortest day of the year in the Northern Hemisphere is the day when the earth’s north pole is tilting 23.5 degrees away from the sun and the south pole is  tilted towards the sun. 
• The spring equinox and the autumn equinox are the only two times of the year when the earth’s axis is neither towards nor away from the sun. This results in equal duration of the day and night.
• Thus, we find that variations in the length of daytime and nighttime from season to season are due to the revolution of the earth on a tilted axis.