Re: Which colur is the moon and why?

That's a really good question! The answer depends upon where you are 
standing - here on earth or on the moon!

If you were standing on the moon, then the surface appears quite gray. 
You can see this by checking out some of the pictures of the moon sent 
back from the Appollo mission. The NASA web site has some of these 
archived or you could look in one of your science books. They would 
likely have a photograph of the moon landings.

The reason that the moon is pretty much a uniform gray and not all of the 
colours that we see on earth is due to the absence of a significant 
atmosphere and living organisms. There is no oxygen floating around so 
iron doesn't rust - no browns. There aren't any oceans or sky, so the 
blue colours are missing. And no plants means no greens. On top of this, 
everything is coated in dust and small particles tend to appear gray in 
colour. It is not uniform in colour, which is why the moon's surface 
appears to be "splotchy" but it is various shades of gray in colour.

If you are standing on the earth and looking at the moon, well, that is a 
whole different story. The moon is like a giant mirror hanging in space. 
It is not a particularly good mirror as it reflects sunlight but not very 
well. The consequence is that the moon we see is lit by the sun. The 
colour is a combination of the natural colour of the moon rock (the gray 
of the moon surface) and the sunlight reflected from the surface.

There is one final factor involved. The earth has an atmosphere and this 
interfers with the incoming light. The sky above us is really black. But 
sunlight scattered throughout the sky makes it appear to be blue. The 
same thing happens with moonlight. It is scattered in our atmosphere. 
Because the moon is only reflecting sunlight, it doesn't turn the sky 
blue. But the blue light is removed from the moon light, leaving behind 
the reds, oranges, yellows, and greens. The result is that when you look 
at a full moon on a clear night, it appears to be "yellow". That is 
its "proper" colour.

Then there are the effects brought about by natural and man-made 
components that we put into the atmosphere. Pollution can change the 
colour of the moon - much the same way that pollution in the atmosphere 
changes the colour of our sunset. However, dust can also have an effect. 
Dust is really good at absorbing the green and yellow light, with the 
result that the moon takes on a much deeper orangy-red colour. This 
occurs when the moon is close to the horizon where the dust in the lower 
atmosphere can interfer and gives us the big, orange harvest moon. When 
harvesting, farmers kick up a lot of dust which helps accentuate the 
effect.

Finally, a "blue moon" isn't blue at all! It is the name given to the 
second full moon in the same month. Because full moons are only about 29 
days apart, it is possible for a full moon to occur on, say, the first 
day and the thirtieth day in the same month. The second full moon is 
called a "blue moon" and is thought to have peculiar powers. It doesn't 
but it is fun to see.

Hope that this answers your question.