Day and Night Length Variation

The variation in daytime and nighttime lengths throughout the year is caused by the earth's tilted axis (23.5° inclination) during its revolution around the sun. When the Northern Hemisphere is tilted toward the sun, it experiences longer days (summer), while the Southern Hemisphere experiences shorter days (winter), and vice versa during the opposite season. Option (a) is incorrect because rotation causes day-night cycle, not seasonal variations. Option (b) is incorrect because the elliptical orbit has minimal effect on day-night length variation. Option (c) is incorrect as it's not the position alone but the tilt's effect on that position. The tilted axis (option d) is the fundamental cause. > Axial tilt is the key: 23.5° creates seasons and varying photoperiods across the year at different latitudes. Answer: d.