Why is there a DARK SIDE of the moon? Does the moon not rotate?

Answer 1

Relative to the Earth, the Moon makes one rotation every 29.5 days. That happens to also be the time it takes for the Moon to complete one revolution around the Earth. This might seem like a coincidence, but it's not.

In the past, the Moon used to rotate much faster than it does now. But over millions of years, the effect of the Earth's gravity has slowed down the Moon's rotation until it became gravitationally locked to the Earth. This is why we always see the same side of the Moon.

It would seem logical to say that at any one time we can see 50% of the Moon's face. If the Moon were flat, that would be correct, however we know the Moon is a sphere. And the spherical shape of the Moon hides the area close to the perimeter and we can, at any one time, see only 41% of the Moon's face.

Even though the same side of the Moon's faces us, we do see a bit more than half of the Moon's face. Over time, because of librations, we can see up to 59% of the Moon's surface.

Librations are irregular motions of the Moon in its elliptical orbit around the Earth. They are measured using longitudinal and latitudinal coordinates. Both are computed from a central point that is at a fixed geographical location on the lunar surface. This point is in the Sinus Medii, a small plain just below and to the right of he large rayed crater Copernicus. Two meridians emanate from this point: the Central Meridian runs north and south, and the Lunar Equator runs east and west.

Different librations affect different sides of the Moon and each contribute added surface area. The added viewable surface area changes from day to day and month to month. Some librations overlap, but the maximum amount of lunar surface that we can see over time is 59%.

The longitudinal libration is produced by the elliptical orbit of the Moon. Because of the nature of the elliptical orbit, the speed of the Moon changes depending on which part of the orbit it is in. When moving from its fastest point (closest to Earth) to its slowest point (farthest from Earth,) the Moon's speed is slowing down. But, because the Moon's rotational speed stays the same, for a period of time the Moon's face is not pointed directly at us, and this "lag" effect allows observers to see an extra bit of the lunar surface. In effect, we are "peeking" around the edge of the Moon! When the Moon is one quarter of the way around the Earth, it is 97 degrees through its rotation.

This libration is called longitudinal because the extra surface areas exposed are along the lines of longitude (perpendicular to the equator.) The total extra surface area we can see from longitudinal librations is about eight degrees.

There is also a libration that is latitudinal. The plane of the Moon's orbit is titled 5 degrees to the ecliptic. For half the lunar cycle, the Moon is above the ecliptic and for the other half it is below the ecliptic. Each of these half cycles expose an extra bit of the Moon. The extra surface area shown during these librations is at the top of the northern hemisphere or the bottom of the southern hemisphere. The total extra surface area we can see from latitudinal librations is almost 7 degrees.

There is one more librations called Diurnal Librations. This librations occurs every day. Observers can "see" over the top of the Moon as it is rising. Likewise they can see under the bottom when it is setting. Diurnal librations are caused because the radius of the Earth adds an extra 4000 miles of height for looking "over" or "under" the Moon when it is on the horizon. This daily libration gives us an extra one percent of lunar surface area for viewing.

Answer 2

Ah - Most confused terminology...

There is no "Dark Side of the Moon."

The Moon rotates around the Earth once a month
with the same side always facing the Earth.

As such a rotation occurs the "FAR SIDE OF THE MOON" is partially, then fully, then partially illuminated by the Sun, then goes into darkness and out again as it comes around the back side of the Earth. So, the FAR SIDE is not dark at all.
We just can't see it from Earth.

The Moon is apparently locked in a dance step with the Earth, not turning any faster or slower than just once a month. Kinda makes you wonder, doesn't it?

Answer 3

It is not technically a "dark side." The moon has a period of roation which aligns it with it's period of revolution. That is, the moon spins on it's axis over the period of time it takes the moon to complete it's orbit.

This means that the same face of the moon is always showing towards the Earth. The side of the moon which faces away from the Earth can only be seen from observers in space, such as astronauts orbiting the moon or space probes sent to photograph it.

The features of the moon have been observed through this method.

Technically the "dark side" of the moon is the side of the moon which is not facing the sun. Any place on the surface of the moon is in darkness for about two weeks, then lit by the sun for about two weeks. Similarly, there is a "dark side" of the Earth, which most places experience for between 8 and 16 hours each day, depending on the seasonal tilt of the planet and the latitude in question.

Answer 4

It is a misnomer to call the side of the moon that does not face the earth the "dark side". It is partially or completely lit at all times when the moon is not seen as full from the earth.

Think about when the moon is half full. You can see half of the side towards the earth is lit and the other half is dark. On the side of the moon facing away from the earth the same thing is happening. just like with any object that is more or less spherical and is lit from the side. Only when the front of the moon is fully lit and the moon is full is the back of the moon fully dark.

Answer 5

The term Dark side of the moon implies that there is a side of the moon that is constantly dark and never recieves any light. This is not true, therefore, the term dark side of the moon is incorrect. Otherwise, there would never be phases of the moon.
There is however, a far side of the moon, a side that is never seen from earth. The side of the moon that faces earth, always faces earth, even though we only see the entire face when there is a full moon. This is because the moon is tidally locked to the earth.

hope this helps!

Answer 6

Tidal forces between Earth and the Moon have slowed the moon's rotation so as that a similar part is often dealing with the Earth. the different face, which isn't seen from the Earth in its entirety (18% of it is seen under some situations), is hence referred to as the "a techniques edge of the Moon". The a techniques part should not be at a loss for words with the "dark part" (the hemisphere that may not illuminated by potential of the solar at a given element in time), as the two are a similar in elementary terms in the time of an entire moon, and by way of a clean moon, the close to part is the dark part. the two the close to and lots sides acquire (on standard) just about equivalent quantities of light from the solar. besides the undeniable fact that, the term "dark edge of the moon" is used usually to confer with the a techniques part

Answer 7

The term "dark side" of the Moon refers to the side that never faces Earth. yes, this side does get lit up when it faces the Sun, but to us and our ability to observe it, it is always unknown or a dark area. The Moon does rotate, but its rotational speed keeps one side always facing the planet. The first persons to see the dark side were the Apollo astronauts in the 1960s.

Answer 8

Regardless of what others here have tried to tell you, the moon *DOES* rotate on its axis. At its equator the rotational speed is 10.3 mph. At the same time it's moving through its orbit around Earth at 2,286 mph. These two velocities are such that one side of the moon always faces away from us.

So, the so-called "darkside" of the moon really isn't dark all the time.

Answer 9

The moon does rotate but it rotates so slowly because of the Earths gravitational pull that we only see one side.

Answer 10

THAT EXACTLY IS WHAT HAPPENS
the tidal effect of the earth over the moon's core (not in the center) "freezed " the moon's rotation
but the dark side of the moon is not a proper way to call it, because it does get light when not in full moon stages
the proper name is the "hidden side of the moon ", hidden from us on earth