NCERT Solutions Curiosity Chapter 12 .1 Rotation of the Earth — In-text Questions
Book page 17012 Updated on2026-09-05
Q1.
You might have also noticed that the Sun rises in the East and sets in the West. Have you ever wondered why?
Answer
Because the Earth rotates from West to East. Anything fixed in the sky therefore seems to move the opposite way — from East to West.
Picture a place on the equator at dawn. As the Earth turns eastward, that place swings into the sunlight from the dark side, and the Sun appears to climb up on the eastern horizon. Twelve hours later the same place turns out of the sunlight, and the Sun appears to slip below the western horizon.
Sunlight always lights one half of the Earth. As the Earth turns from West to East, a place first crosses into the lit half (sunrise) and later crosses out of it (sunset).
Check it yourself: hold a ball in a beam of torchlight in a dark room and turn the ball slowly anti-clockwise when seen from the top. A dot marked on the ball moves into the light and out of it — one rotation, one day and one night.
Q2.
When we view from the Earth, the Sun appears in the East, moves across the sky from the East to the West and disappears in the West. Does it indicate that the Sun is moving in the sky? Or might it be that the Earth itself is turning around and the Sun just appears to move?
Answer
The second one is correct — the Earth is turning around, and the Sun only appears to move.
The merry-go-round of Activity 12.1 settles it. Sitting on a merry-go-round that turns anti-clockwise, you see every tree and building swing past you in the clockwise direction, entering your view on the left and leaving it on the right. You know perfectly well that the trees are not moving — you are.
Our situation on the Earth is the same, only slower and much larger. The Earth carries us around once in about 24 hours, from West to East, so the Sun enters our view in the East and leaves it in the West.
Why it happens: motion is always judged with respect to something. Since we cannot feel the Earth's smooth spin, we naturally credit the motion to the Sun. This is called apparent motion — the Moon and the stars show it too, and for exactly the same reason.
Did you know? Aryabhata explained this in the fifth century CE with a boat: a man moving forward in a boat sees the stationary bank slipping backwards. He even gave the length of one rotation as about 23 hours 56 minutes 4.1 seconds — remarkably close to the value accepted today.