Variations in the length of daytime and night time from season to season are due to

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Accepted Answer

revolution of the earth on a tilted axis. While the Earth's daily rotation creates day and night, the variation in the length of those days and nights throughout the year is fundamentally caused by the Earth revolving around the Sun on a tilted axis. Direct Breakdown of the Options: Revolution on a Tilted Axis (Option d - Correct): The Earth’s axis is tilted at an angle of 66.5° to its orbital plane (or 23.5° from the perpendicular). Crucially, this tilt remains fixed in the same direction throughout the Earth's annual revolution around the Sun. Because of this, the Northern and Southern Hemispheres alternately lean toward and away from the Sun. When a hemisphere is tilted toward the Sun (summer), the circle of illumination cuts across it unevenly, keeping that hemisphere in the sunlight for a longer duration of its daily rotation (longer days, shorter nights). When tilted away (winter), it spends more time in the Earth's shadow (shorter days, longer nights). Earth's Rotation on its Axis (Option a - Incorrect): Rotation is responsible for the daily occurrence of day and night. However, if the Earth rotated on an axis that was perfectly vertical (0° tilt) relative to its orbit, the circle of illumination would perfectly bisect every latitude. Consequently, every place on Earth would experience exactly 12 hours of day and 12 hours of night, 365 days a year, with absolutely zero seasonal variation. Latitudinal Position (Option c - Incorrect): Latitude determines the magnitude (or extreme) of the variation, but it is not the root cause. For example, because of the tilt, daylight variation is virtually zero at the Equator, but increases dramatically as you move toward higher latitudes, culminating in 6 months of day/night at the poles. Latitude is a geographical variable, but the astronomical driver is the tilted revolution. Elliptical Revolution (Option b - Incorrect): The Earth's orbit is indeed elliptical, meaning the Earth is slightly closer to the Sun in January (Perihelion) and further away in July (Aphelion). This slight variation in distance marginally affects the intensity of solar radiation and the length of the seasons themselves (due to varying orbital speed), but it has no bearing on the changing ratio of daylight to nighttime hours. For comprehensive details on the variations in the length of day and night times, see the explanation for 4th question in the 2024 PYQs on Physical Geography (World)