The near side, the far side of the moon...?

Question

Since the moon always has the same side facing the earth (due to tidal effects), can we see only 50% of the moon's surface? Explain, please.

Answer 1

The Moon  revolves synchronously with the Earth, it rocks slightly so that through a complete cycle we see slightly more than 50% The other side of the moon has fewer craters.

Answer 2

The moon always has one side pointed towards the earth.  Essentially the moon rotates on its axis at a rate that equals one full orbit of the earth.

The moon causes tidal bulges in the earth (essentially pulling the sea and land up a bit).  The land and sea resist this and take some time to get pulled up.  As a result the tidal bulge lags behind the moon a bit causing a sort of drag on the moon.  The result is a transfer of angular momentum (takes energy to do all this...no free rides).  Over time the moon loses velocity till it is tidally "locked" and only one face points towards the earth.

Note this works both ways.  The transfer of energy continues and eventually the earth will likewise only point one side towards the moon (essentially the moon will seem to hang over one spot).  Now the earth is rotating a bit faster than the moon orbits and the tidal bulges are ahead of the moon.  The effect is causing the moon to move away from us every year (by about 1/3 of a centimeter) as well as the earth's rotation slowing down (by about 37 microseconds every year).

Don't hold your breath though.  This mutually "locked" state will take longer than the lifetime of our sun to occur.  No one will be around to see it.

Answer 3

you can never see 50% of the moons surface at once.   the only way that could happen is if the moon were exactly the opposite side of the earth as the sun,  at which time its enveloped in the earths shadow for an eclipse.  Even on nights with a full moon, you cannot see half the moon--there is always a sliver in darkness

Answer 4

we can only see about 1/2 of the moons surface because the amount of time it  takes for the moon to orbit the earth is equal to the amount of time it takes the moon to complete one full spin on its axis.

its hard to explain through words but if you think about what i said it should make sense

Answer 5

The moon is in synchronous rotation, meaning that it keeps nearly the same face turned towards the Earth at all times.

But small variations in the moon's rotation and orbit (called libration) let us see about 59% of its surface from Earth (but only half at any one time).

There are 3 forms of libration that affect the moon:

1. Libration in longitude: because the moon's orbit around Earth is not perfect, sometimes the moon's rotation "leads" and sometimes "lags" behind its orbital position.

2. Libration in latitude: the moon's axis of rotation is slightly inclined to the normal to the plane of its orbit around Earth.  

3. Diurnal libration: the small daily oscillation from Earth's rotation - this "rocking" carries an observer first to one side and then the other side of the imaginary line between Earth's center and the moon's center.

Answer 6

Yes, at any one time one can only see 50% of the Moon's surface.

However, due to libration, which allows us to see an additional 9% of the Moon at different times as it orbits the Earth..

This occurs because even though the Moon presents the same side to the Earth at all times (because of the tidal effects), the Moon's orbit, being ellipitical, it causes a slight discrepancy, and causes the Moon to oscillate with respect to the Earth.  

There's also diurnal "libration" when an observer on one side of the Earth sees "around the edge" of the Moon slightly, whereas another observer on the other side does not, because of the distance (7,900 miles, NOT 12,500 miles) apart, as you would use the diameter of the Earth as a reference, and NOT the distance on the Earth's surface.

I hope I explained this as best as I could.

Answer 7

Actually, the Moon wobbles a little during its orbit, so we can see a little more than half of the Moon's area during a lunar cycle.