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

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

The Earth's axis is tilted relative to its orbit, and the Earth keeps this tilt as it goes round the Sun. So the Sun's rays fall differently on each hemisphere through the year. This changes the length of day and night from season to season. Both the tilt and the revolution are needed.

• ✓ (d) The Earth keeps its tilted axis as it orbits the Sun. Because of this, each hemisphere is tilted towards the Sun for part of the year and away from it for the rest. Days are therefore longer in summer and shorter in winter.
• ✗ (a) Rotation on the axis gives the daily cycle of day and night, about 24 hours. It does not make day length change across seasons.
• ✗ (b) The elliptical orbit alone does not explain it. Without the tilt, day and night would stay roughly equal everywhere through the year. The tilt is the key factor.
• ✗ (c) Latitude decides how large the seasonal variation is at a place. It is not the cause of the variation itself.

Remember · Seasons and the changing length of day and night come from revolution combined with the 23½° axial tilt. Rotation alone gives only day and night.

📘 Read it in NCERT: Class 7 Curiosity, Ch 12 (practise this chapter) · Class 9 Exploration, Ch 13 (practise this chapter)

Question: UPSC Civil Services (Preliminary) 2013, General Studies paper. Explanation: Minimalist IAS, checked 25 Oct 2026 (how we verify). · Report an error