Diagram showing the cause of a Total Lunar Eclipse

The Moon travels into the Earth's shadow (from the place as indicated by the hollow circle on the diagram). Slowly the Moon approaches the exact opposite side of the sky to the Sun, where the Earth blocks out all direct light falling on it. Normally this would be the time of Full Moon, but now we're in for a treat due to the perfect line-up of the three big objects.

As the Moon travels into the Earth's shadow you will notice the left side of the Moon gradually darkening until Totality is achieved (the filled-white circle). Strangely the Moon often takes on a reddish-orange-brown mix of colour, and is hardly ever black. This is because indirect sunlight is still reaching the Moon. This is an effect of the Earth's atmosphere which lets the red part of the Sun's light filter through to dimly light the Moon.

Take a look at the image on the right to see this colour in action. Just imagine standing on the Moon during a Total Eclipse. The Earth itself would be a black disc, but our atmosphere would be glowing red. This is the ring of sunrises and sunsets that are happening around our world.

The diagram below shows the Moon moving through the shadow of the Earth during a Total Eclipse of the Moon. Most months the Moon moves above or below this shadow, that's why Lunar Eclipses don't happen at each Full Moon.

Because the Sun is much bigger than the Earth, our planet's shadow has two bits: the darkest part is called the Umbra. Here you will see no light from the Sun. The other, less important part, is the Penumbra where you would catch a part-view of the Sun if you were standing on the Moon (with a spacesuit on!).

Diagram showing how a Total Lunar Eclipse happens when the Moon moves through the darkest part of the Earth's shadow (the umbra)

As the Moon goes into eclipse and dims the sky gets darker too. You may not have realised how the bright Full Moon causes the sky to be awash with a blue haze allowing only the brighter stars to be visible. During a Total Lunar Eclipse this darker Moon means the fainter stars can come out and we end up with an eerie sight of (usually) a deep red Moon surrounded by twinkling stars.

Totality can last for over an hour and a half, so the whole thing is quite a gentle process. You need no special equipment, and if your house is pointing in the right direction you don't even need to go outside! You can simply gaze spellbound out of your window. Now, that's luxury.

Using the diagram above again: A Partial Lunar Eclipse is when only part of the Moon travels through the umbral shadow of the Earth. During a Penumbral Lunar Eclipse you may not even notice anything happening! The Moon doesn't touch the umbral shadow and so sunlight still reaches the lunar surface. There is only the slightest darkening during a Penumbral Eclispe - I don't think it's worth getting out of bed for if it happens in the middle of the night.