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Last updated: 08 May 2006 1124 BST
Pic: Mark Lawrik-Thompson
Graphic: Astronomy: your questions answered
Norfolk astronomer and Chairman of the Norwich Astronomical Society Mark Thompson is here to answer your questions about space.

The Moon

Why can I still see the Moon during the day?

Read the answers to your questions on the Moon by local astronomer, Mark.

Why does the moon not spin off into space?

Answer: Generally, the Moon does not spin off into space because it is held in place by the Earth's gravity; the same thing that holds you and me on the surface of the Earth. Having said that there are a number of reasons why the Moon is actually getting a little further away each year at a speed of about 4cm per year.

When do we get eclipses?

Answer: There are two types of eclipses, eclipses of the moon (or lunar eclipses) and eclipses of the sun (or solar eclipses). Lunar eclipses occur when the Earth stops light from the Sun reaching the Moon. Solar eclipses happen when the Moon stops light from the Sun reaching the Earth. Lunar eclipses are much easier to see because you can see them anywhere on the Earth that you can see the Moon, Solar eclipses are much harder to see as you have to be in very special places to see them.

How long does it take for the moon to orbit the sun? I have this question for homework, but cannot find the answer anywhere!

Answer: The Moon doesn't orbit the Sun, it orbits the Earth. It takes the Moon about 27 days to complete one orbit.

Does the moon have a dark side and does it turn blue during the blue moon phase?

Answer: The Moon takes about 27 days to spin once on its axis but also takes the same time to complete one orbit around the Earth. This means that the same half of the Moon always points to the Earth.

So there is a 'side' that we never get to see but it does receive sunlight just like all parts of the Moon.

The term of "blue moon" refers to the second full moon in a month. This doesn't happen too often hence we say that "something happens once in a blue moon".

It doesn't actually turn blue though! This has reference to a 19th century proverb but that's a rather long story. The next blue moon will be in June 2007.

Why doesn't the moon have a atmosphere?

Answer: The Moon does have an atmosphere but it's very thin. The reason it doesn't have a thick atmosphere like Earth is that there is not enough gravity to hold on to it.

Picture: the Moon during an eclipse
The Moon during an eclipse

Is the distance between moon and earth changing?

Answer: The Apollo Space missions left special mirrors on the Moon. This allows us to bounce a laser beam off these mirrors and very accurately measure how long it takes the laser to get back to the Earth.

By doing this we know that the Moon is moving away from us at a distance of about 3.5 cm per year.

What are Moon dials and what are they used for, are they different to sundials?

Answer: There are a number of different items called Moon dials. The most common one is attached to a normal clock and is used to show the phase of the Moon at that moment in time.

The other sort as you guessed, similar to a sun dial and is used to tell the time. Click here to make a sun dial

Why do people on Earth always see the same face of the Moon?

Answer: The gravity of the Earth pulls on the Moon and the gravity of the Moon pulls on the Earth. This has been happening for the past few billion years and so eventually the Moon and Earth have 'locked' in on each other due to the pull of gravity.

Many of the other planets in the Solar System have moons and these too keep the same face pointing to their planet. Its called synchronous rotation.

Why are there different size craters on the moon?

Answer: Craters are formed when pieces of rock smash into the surface of the Moon. The same thing has formed craters on Mercury, Venus, Mars and even the Earth.

A larger rock smashing into the surface will cause a bigger crater than a smaller one and a piece of rock that smacks into the surface very fast will produce a bigger crater than one travelling slower.

Why do we see the moon in the daytime?

Answer: The Moon goes around the Earth and the Earth goes around the Sun. This movement, along with the spin of the Earth means that the Moon and Sun seem to move around our sky quite independently of each other.

This means that often both the Moon and Sun will be above the horizon at the same time.

We can see the Moon because its being lit by the Sun. So as long as nothing stops sunlight getting to the Moon, like the Earth does during an eclipse, then we will be able to still see the Moon in the daytime sky

Read more: The Moon »

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See also

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Astronomy index

Ask the astronomer

International Space Station

Make a rocket

Make a sundial

New Planet

Planet Jupiter

Planet Mars

The Moon

Planets Pluto, Neptune and Uranus

Planet Saturn

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The Star of Bethlehem

The Sun

Your questions answered

Venus passes in front of the Sun


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