Why does it take the moon 27.3 days to complete one rotation?

Answer 1

Because the Apollo missions went to the Moon on the barest minimum amount of fuel. If you had a little more fuel, you could get there in one day, and if you had a LOT more fuel, you could get there in one HOUR.

Answer 2

I'm sorry, there are some errors here. Our Earth rotates around the Sun in about 365 days. The Earth revolves on it's axis in 24 hours.

Now it is true that it is not exactly 24 hours. There are very, very minor, but measurable, differences. But not so great as 21 minutes.

At no point has our Earth spun in 23.39 minutes in Mankind's history.

Answer 3

That's how long it takes for the Moon to orbit the Earth once.

However, the cycle of the phases of the Moon is 29.5 days. The difference occurs because the Earth is continuing in its orbit while the Moon is orbiting the Earth, and after 27.3 days, the Earth has moved so far in its orbit that it takes the Moon another 2.2 days for the Moon to get back into the same relative Earth-Sun-Moon orientation.

Answer 4

Well - this is an interesting one as it requires a term of reference.

Whilst the Moon is orbiting the Earth, the Earth is also orbiting the Sun and the Sun is in orbit around the center of our galaxy, and, the galaxy, is careening at a substantial velocity through the cosmos!

The Moon's orbit about Earth has it, on average, 390 917kms from Earth's center, as such it travels in one full orbit ~2 456 522kms.

Over the same period however, the course of the 27-odd days, the Earth has moved ~69 465 600kms around the sun in its orbit.

Over the same period, the Sun has travelled ~513 216 000kms in its orbit about the center of the galaxy.

Over the same period, the Milky way galaxy has travelled ~1 217 721 600kms in relation to the cosmic background radiation which is used as a universal reference frame.

So, I guess if you could somehow determine the average radial velocities for all these and bring to back to the Moons point of view, you have the real distance travelled by the Moon as it undertakes one orbit.

Answer 5

That's the orbital period that results from the gravitational coupling of two bodies
with the masses of the Earth and Moon, separated by the distance at which they're
presently orbiting their common center of mass.

Answer 6

dont you mean why does the earth take 23 hours and 56 minutes to rotate.

Answer 7

It does not take 24 hours for earth to orbit the sun. It takes 24 hours for earth to spin on it axis and it takes 365 days and 6 hours to orbit the sun.

Answer 8

You go to the Moon while fighting Earth's gravity. You return with Earth's gravity pulling and speeding you up.

Answer 9

Somebody decided - in the remote past - to divide the day into 24 equal periods. Pressumably such a number was chosen because it has many factors.

Answer 10

Yes, when the orbital period is rounded off, that's a good number.