The Moon.

Yes, relative to "space" but no, relative to the Earth. It always keeps the same aspect facing towards the Earth. In effect, it rotates once each time that it orbits the Earth. It orbits the Earth once in a lunar month of about 27 days.
 
It used to spin but tidal forces have slowed it down over the years to make it stop. Eventually these same forces will pull it out of the sky but I wouldn't worry about it just yet. :D
 
I don't claim to fully understand the physics (perhaps others could explain?) but when two bodies orbit each other in the way the Moon and Earth do the smaller one always ends up with a rotational period that is more or less the same as it's orbital period.
 
electrosys said:
I was looking at it the other night and wondering why, if the moon's surface is actually a brown sandy colour, how come it always looks silver to us ?

And then on further consideration, I decided that I didn't really care ...
Click to expand...
How do you know the surface is a brown sandy colour?
 
little_roundtop said:
I don't claim to fully understand the physics (perhaps others could explain?) but when two bodies orbit each other in the way the Moon and Earth do the smaller one always ends up with a rotational period that is more or less the same as it's orbital period.
Click to expand...

Tidal locking. As the bodies rotate, even the solid parts of the surface have a tidal bulge. The effect of this bulge moving across the surface gradually slows rotation down until they face each other. The earth is slowing in the same way but, being more massive, hasn't stopped - yet.
 
little_roundtop said:
I don't claim to fully understand the physics (perhaps others could explain?) but when two bodies orbit each other in the way the Moon and Earth do the smaller one always ends up with a rotational period that is more or less the same as it's orbital period.
Click to expand...

Tidal forces will gradually reduce the energy of rotation until eventually it will become "locked" because of a slight bulge which prevents further rotation. Before this happens there is sufficient energy to move that bulge around just like the tides on earth. Obviously it's not water on the moon, but the rock is affected slightly.
 
Gorf said:
How do you know the surface is a brown sandy colour?
Click to expand...
Good point. Seems that somebody, somewhere, is lying ...

According to the Apollo photographs, it's mostly brown sand (pretty-much the same colour as the Nevada desert ... Hmmm). But according to the Wiki entry (so it must be true), it's as black as coal.

Having read the Wiki entry, what I didn't realise was just how BIG the moon is - as with the same human arrogance that once saw the Earth as being the centre of the cosmos, we have come to view the Moon as being only a satellite of the Earth, rather than the Earth being the larger partner of a bi-planetary system.
 
electrosys said:
Good point. Seems that somebody, somewhere, is lying ...

According to the Apollo photographs, it's mostly brown sand (pretty-much the same colour as the Nevada desert ... Hmmm). But according to the Wiki entry (so it must be true), it's as black as coal.

Having read the Wiki entry, what I didn't realise was just how BIG the moon is - as with the same human arrogance that once saw the Earth as being the centre of the cosmos, we have come to view the Moon as being only a satellite of the Earth, rather than the Earth being the larger partner of a bi-planetary system.
Click to expand...

Hmmm...I suspect there is more to it than just an innocent fib.

You see, when the earth rotates so the sun is behind us, the sky above us goes dark.

This is because our arc of vision restricts actually seeing the sun on the other side because light travels in straight lines, not curves.

Therefore it follows that because the light from the sun continues to stream past the earth (as the earth is a mere minor obstacle in its path) it illuminates the stars....

The stars are in the heavens all the time...we cannot see them in daylight because of the sun's presence and glare...but when the glare is removed...they become visible.

That far is obvious.

Here is a curiosity...

When Patrick Moore interviewed Neil Armstrong and Buzz Aldrin after their moon landing he asked them if when on the moon (or indeed on the way there) they could see the stars.

Their reaction to this question was very peculiar.:eek:

They looked shocked and were lost for words. They looked at each other with what appeared to be embarrassment...but declined to give an answer one way or another.

What do readers make of this?:D
 
An Earth day is 24 hours. A Lunar day is about 28 days (i.e. it spins on its axis once every time it orbits the Earth).

Now, to see clearly what you were doing whilst on the moon you would need sunlight. And, in order for radio signals to go back and forth easily between the astronauts and mission control, you would need to land on the side facing the Earth. (There weren't lots of satellites back then that you could use to bounce signals back to Earth).

So, I'm guessing the whole duration of their time on the moon was during lunar daylight. I'm not sure exactly how long they were on the surface, but it was only only a couple of days, wasn't it? Therefore, (unless they happened to experience an eclipse of the Earth) they would not have seen the stars for the same reason that you don't see them during the day on Earth.

They would have seen them whilst in orbit round the Earth and when in orbit round the moon (on its dark side).

I guess they just hadn't adjusted their minds from an Earth day (where you see stars every 12 hours) to a Lunar day where you have to wait 14 days.

Or am I totally wrong? :confused:
 
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