Eva Urlwin, of St Mark's School, asks :-

Why does the moon shine when it's only rock?

Jim Coxon, an amateur astronomer and sometime supervisor of the Canterbury Museum's Planetarium , responded.

The Moon, especially when it is full, certainly does seem to shine very brightly. It is often bright enough to be seen during the daytime.

As you already know, rock does not give off light. The Moon therefore, has no light of its own. When the Sun has set below the horizon, and you can no longer see it, its light can still shine onto the Moon's surface. The Moon reflects some of the light it receives from the Sun back to you. in much the same way as a mirror reflects light. It might surprise you to learn that the Moon is in fact, a very poor 'mirror'. The Moon reflects less than a tenth of the sunlight which falls on it.

Stars are hot bodies that emit their own light but they are so far away from us that they only appear as points of light. Planets, which form part of our Solar System (the Sun's system), are much closer to us but do not emit their own light so we see them only by reflection of sunlight. The closer, brighter planets -- like Jupiter and Venus, appear as tiny disks. They do not appear as points of light, like stars.

Because the Moon is closer still to the Earth, compared to the other planets, we see it as a larger disk. As a result, it appears brighter.