Variations in the length of daytime and nighttime from season to season are due to
[UPSC Civil Services Exam – 2013 Prelims]
(a) The earth’s rotation on its axis
(b) The earth’s revolution round the sun in an elliptical manner
(c) Latitudinal position of the place
(d) Revolution of the earth on a titled axis
Answer: (d)
Explanation:
- The duration of daylight, or day length, differs from one location to another on the Earth. The equator receives roughly 12 hours of daylight every day, while the North Pole experiences 24 hours of daylight during some summer months and complete darkness during winter months.
- The occurrence of day and night is the outcome of the Earth’s rotation on its axis, which is tilted at an angle of 23.5 degrees. Consequently, during the Earth’s revolution around the sun, the polar regions experience extended periods of sunlight in summers and prolonged periods of darkness in winters.
- Regions situated above 66.5 degrees, such as the Arctic and the Antarctic, witness days of unceasing darkness or light. The Northern Hemisphere’s longest day of the year or summer solstice takes place when the Earth’s North Pole tilts 23.5 degrees towards the sun. Conversely, the shortest day of the year or winter solstice in the Northern Hemisphere happens when the Earth’s North Pole tilts 23.5 degrees away from the sun, and the South Pole points towards it.
- Only two times a year, the spring equinox and autumn equinox, the Earth’s axis does not point towards or away from the sun, resulting in equal durations of day and night. Thus, we can attribute the variations in the length of day and night during seasons to the Earth’s revolution on a tilted axis.
Therefore, option (d) is the correct answer.
