Question

The size of the visible part of the Moon ………….. gradually after the full moon day till the new moon day.
A) Remains the same
B) Increases
C) Decreases
D) Either increases or decreases

Answer 1

Hint: The Moon revolves around the Earth at a uniform speed. It takes around 30 days for the Moon to complete its one cycle around the Earth. When the Sun and the Moon are on the same side of Earth all in a line, it is called the new moon day. We usually consider this as day 0 of the cycle of the Moon. If the Sun and the Moon are on different sides of the Earth in a line, it's called a Full moon day.

Complete step by step solution:
Moon does not have its light. Hence, we can see only that part of the Moon that is illuminated by the Sun. When the Moon is in the East, it lies somewhere between the Earth and the Sun. Thus the illuminated part faces the Sun, and the dark part faces the Earth. Therefore we cannot see any moon in the sky. This is the new moon day. After this, gradually, the Moon starts moving towards the West through the North. As it moves in this path, the Moon's illuminated part slowly faces the Earth and we see the phases of the Moon from New Moon to the crescent moon. Then half-moon finally converts into the full Moon; when it reaches the West, the entire illuminated part of the Moon faces the Earth, and it is the full moon day. Then the Moon gradually starts moving towards the East once again through the south, and the visible part of the Moon decreases in the same manner until the new moon day, and the cycle keeps repeating itself. Thus we see the phases of the Moon. It takes 15 days for the Moon from new moon day to full moon day and another 15 days from full moon day to new moon day.

Therefore the correct option is (C).

Note: The phases of the Moon depend on its position about the Sun and Earth. As the Moon makes its way around the Earth, we see the Moon's surface's bright parts at different angles. These are called 'phases' of the Moon.