If the clouds allow you will see a stunning lunar eclipse this evening, low in the sky from 9pm towards the south-east. Prof Teresa Anderson explained on BBC tv this morning..with a melon/earth and onion/moon (where the moon goes behind the earth, which blocks the light of the sun from the moon).
The lunar eclipse, which takes place over a matter of a few hours, as explained on Popastro:
The Moon will rise fully eclipsed, so we won’t see the early stages of the event. But that will actually add to the spectacle, because the Moon will be a deep red colour against the blue sky (assuming of course it’s good and clear!) The media are calling it a ‘blood Moon’ – though that’s not a term astronomers traditionally use!
A lunar eclipse, just to remind you but you really knew anyway, happens when the Moon goes into the Earth’s shadow, so it goes from being the familiar bright moon to a very dark one. As well as being interesting to watch, lunar eclipses can be very beautiful because of the unusual colours that occur.
Normally during a lunar eclipse the Moon starts out as a regular full Moon, a complete disc, but then we start to see its left-hand edge become gradually darker until it seems to have a circular bite taken out of it. This is quite different from the phases of the Moon, caused by the Sun shining on it from different angles as the Moon goes around the Earth every month – starting with a crescent, then going to a half Moon, then gibbous when it’s nearly a complete disc, then Full. A lunar eclipse can only take place at full Moon, because that’s when the Sun is exactly opposite the Moon in the sky. In fact, the true full Moon always rises exactly opposite the Sun, and at the time the Sun is setting. And it doesn’t happen at every full Moon, because more often than not the tilt of the Moon’s orbit means that it goes above or below the Earth’s shadow.
So to continue the story of the eclipse, which takes place over a matter of a few hours, eventually the Moon is completely within the Earth’s shadow, so all the Sun’s light is cut off. But it doesn’t go completely black. There’s always a bit of light refracted around the edge of the Earth, even when the Sun is completely covered by the Earth. If you could stand on the Moon during a total eclipse you’d see the Sun gradually being hidden by the Earth’s larger disc, but even when it’s totally behind the Earth there would be red light bent around by our atmosphere. (read more on Popastro)