Why are day and a year on the moon the same length?

Answer 1

Magic.

Answer 2

The Moon orbits around the Earth in just over 27 days. One complete set of the Moon's phase changes is commonly called a "lunar cycle" and that takes a little longer because the Earth and Moon orbit the Sun. That's the Moon's "solar day". (The word 'month' derives from the word 'Moon', and refers to this lunar cycle of roughly 29 days.) The Moon does not orbit around the Sun independently of Earth. The Moon does orbit around the Sun, but only because the Moon orbits the Earth and accompanies the Earth in its yearly journey around the Sun. These are just the basics; we won't get into precise definitions of orbital periods, or precise lengths of time of various movements.

The Moon also rotates on its axis (in one "sidereal day"). It completes one rotation during the course of one orbit around the Earth. This is because the Moon is 'tidally locked' with the planet Earth. So, the Moon rotates one full time during the course of one orbit. The fact that one rotation of the Moon is equal to one lunar orbit around the Earth is what causes the same side to always face Earth (with some slight differences that we won't cover here). A lunar "year", the Moon's orbital period around the Sun, is almost exactly the same length as an Earth year.

So, a day and a year on the Moon are NOT the same length.

It's the Moon's "sidereal day" that equals its period of revolution around the Earth.

Answer 3

The moon rotates around it's axis (in it's day) in the same amount of time as it orbits the Earth (it's year).

Answer 4

There is no particular significance to "year" on the Moon. We would say that the Moon goes around the Earth in one "month", and in that case, yes, the lunar day is equal to the month.