Correct Option
The correct option isTilt of the Earth's axis away from the Sun
Explanation
The variation in the duration of day and night across different times of the year is primarily governed by the Earth's revolution around the Sun combined with the inclination of the Earth's axis. This astronomical arrangement determines the angle of incidence of solar rays and the length of time a specific location remains exposed to sunlight.
Option Analysis
- Faster rotation of the Earth is Incorrect: The Earth rotates on its axis at a nearly constant speed. While there are minute fluctuations, they are not significant enough to cause the seasonal variation in day length.
- Greater distance from the Sun is Incorrect: The distance between the Earth and the Sun changes due to the elliptical orbit (Perihelion and Aphelion). While this affects the intensity of insolation received, it does not determine the length of the day. For instance, the Earth is closest to the Sun (Perihelion) around January 3rd, which coincides with winter in the Northern Hemisphere when days are shortest.
- Tilt of the Earth's axis away from the Sun is Correct: The Earth's axis is tilted at an angle of 66.5° to the plane of its orbit (or 23.5° from the vertical). During the winter season in a hemisphere, that hemisphere is tilted away from the Sun. Consequently, the circle of illumination does not cover the pole of that hemisphere, and locations within that hemisphere spend more time on the dark side of the Earth during rotation, resulting in shorter days and longer nights.
- Increased cloud cover is Incorrect: Cloud cover influences the transparency of the atmosphere and the amount of solar radiation reaching the surface (heat budget), but it does not alter the astronomical duration of daylight hours.
Key Takeaway: The inclination of the Earth's axis (tilt) relative to its orbital plane is the fundamental factor responsible for the variation in the length of day and night and the occurrence of seasons.