Royal Observatory Greenwich blog
From the shadow of the Moon, to the shadow of the Earth

On Saturday the 16th of August, we get to enjoy a lunar eclipse! A lunar eclipse occurs when the Moon goes into the shadow of the Earth.

It is no coincidence that we have a solar eclipse (when the Moon casts a shadow onto the Earth) and a lunar eclipse (when the Earth casts a shadow onto the Moon) just a fortnight apart…

Because the orbit of the Moon is tilted, it travels from the South of our flat solar-system to the North, and back South again every month. During the eclipse on the 1st of August, the Moon was travelling from the North down to the South… and as it did so it happened to pass in front of the Sun. On the 16th of August, the Moon is heading North again, passing though the shadow of the Earth on its way.

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It is also no coincidence that we are having a pair of eclipse’s six months after the last pair! This is because the nodal axis of the lunar orbit happens to be in line with the Sun at the moment, which happens every six months because the Earth orbits the sun every year (see the graphic to the left, and my earlier post from the February eclipse season for more details).

This lunar eclipse will be visible from everywhere with the exception of the continent of North and central America (see this map). The animation I have created below using the excellent (and free!) Celestia software explains why the eclipse is not visible from the top half of the America’s… our planet gets in the way!


But for us here in the UK, the Moon will be rising in eclipse, so we have some tremendous and unique photographic opportunities to look forward to!

And what will the eclipse look like? Well, the Moon will turn either a deep red, a pink colour or maybe grey… we really don’t know! Take a look and find out for yourself! It all depends on the atmospheric conditions of the Earth at the time of the eclipse, since some sun-light will bounce through our atmosphere and illuminate the Moon even when it is in the shadow of the Earth.

The Moon will first enter the outer shadow of the Earth at 18:25 GMT (19:25 British Summer Time) – although, you may not even notice. An hour later, at 19:36 GMT (20:36 BST) the Moon begins to go into the dark heart of the Earth shadow, and that’s when the eclipse really begins!
The Moon is in the middle of the Earth’s shadow by 21:10GMT (22:10BST), and has left the dark shadow by 22:44 GMT (23:44 BST). The entire eclipse ends at 23:55 GMT (00:55 BST).

And for those of you too impatient to wait, below is a time-lapse movie of a lunar eclipse I saw back in March 2007! (click for full details).

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