Why are the moon's oon translation AND rotation exactly 28 days... A coincidence?

Question

And is there a part of the moon that never gets hit by light?

Answer 1

It's not a coincidence. It is the result of tidal locking, a process by which the Moon loses orbital and rotational energy to the Earth. In essence, the gravitational pull between the Earth and Moon causes both bodies to bulge towards each other. The direction of the Earth's bulge changes as the Moon orbits it, but the bulge lags behind the Moon and causes a gravitational drag.

The Moon does not have a part that is never hit by light, except for a few very deep craters near its poles. The Moon's orbit and axis are tilted very little from the ecliptic (the plane in which the planets orbit), so it's possible for a moderately deep crater near the pole to never have the crater's floor facing the Sun at all. When we refer to the "dark side of the Moon," we typically mean the part that can never been seen from Earth; the fact that the Moon's period of rotation is equal to its period of revolution means that the same side of the Moon always faces the Earth. But when the Moon is between the Earth and Sun, the part of the Moon that faces away from the Earth is facing directly at the Sun and it experiences day.

In total, slightly more than half of the Moon's surface can be seen from various locations on Earth at various times. The orbital velocity of the Moon varies over the course of its elliptical orbit, causing it to twist forwards and backwards a little bit as seen from Earth. Also, the Moon's orbit is inclined to the tilt of the Earth's axis, enabling people on Earth to see over and under the moon a little bit further at different times.

Answer 2

You asked 2 questions.

First, it is no coincidence that the Moon rotates and revolves at the same rate, It is tidally locked. That means that slight out of round conditions on both the Moon and Earth have cause small gravitational forces that tend to force this rotation rate. These same forces are slowing the rotation rate of the Earth, making the day longer by a tiny fraction if a second each year.

Second, There are a few crater floors near the Moon's poles that never have direct sunlight falling on them. There is a possibility that water may exist there as permanently frozen ice, so NASA is very interested in that as a source of water for a Moon base. Water can not only be used for drinking and washing, but electricity can be used to break it into hydrogen and oxygen which can be used as rocket fuel. If rockets could refuel on the Moon, space flight could be much more efficient and cheaper.

Answer 3

Its a phenomenon called "tidal locking." Its not unique to the Earth -moon system (smoe of the moons of Jupiter and Saturn do the same thing).

The orbital period and rotational period of a much smaller orbiting body are forced into sync by the dominate gravity of the larger body.

Answer 4

It's due to tidal locking and it a pretty common occurance in the solar system. Other bodies tidal locked are:

Locked to the Sun-
Mercury (in a 3:2 rotation:orbit resonance)

Locked to Mars-
Phobos
Deimos

Locked to Jupiter-
Metis
Adrastea
Amalthea
Thebe
Io
Europa
Ganymede
Callisto

Locked to Saturn-
Pan
Atlas
Prometheus
Pandora
Epimetheus
Janus
Mimas
Enceladus
Telesto
Tethys
Calypso
Dione
Rhea
Titan
Iapetus

Locked to Uranus-
Miranda
Ariel
Umbriel
Titania

Locked to Neptune-
Proteus
Triton

Locked to Pluto-
Charon (Pluto being itself locked to Charon)

Answer 5

It's really 27.32 days and is spin locked with the earth due to concentrated mass in the part of the moon that faces us.