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May's lunar eclipse

Mid-totality during the lunar eclipse of 21 January 2000© Fred Espenak, NASA/GSFC On the evening of 4 May British astronomers and the general public were able to witness one of the night sky’s most beautiful events - a total eclipse of the Moon.

Total lunar eclipses occur when the full Moon is exactly in line with the Earth and Sun and moves into the Earth’s shadow. They can be seen wherever the Moon is above the horizon and so from a given spot on the Earth’s surface are much more common than solar eclipses, although they are still unusual events. This eclipse is visible from Europe (including the whole of the British Isles), Africa, Asia, Australia and South America. Although in the UK the Moon will be low throughout the event, this could make an attractive scene and a good target for landscape photographers.

The Moon will enter the lighter, penumbral shadow of the Earth at 18.51 BST and the darker umbral shadow at 19.48 BST. It will be completely immersed in the Earth's shadow (totally eclipsed) by 20.52 BST. From London moonrise is at 20.22 BST so the Moon will already be partially eclipsed when it edges above the south-eastern horizon.

Diagram illustrating the passage of the Moon through the penumbra and umbra of the Earth's shadow. P1 and P4 indicate where the Moon enters and leaves the penumbra, U1 and U4 mark where it enters and leaves the umbra and U2 and U3 are the beginning and end of totality. Image: © Fred Espenak, NASA/GSFC

During the total eclipse the Moon will darken considerably but will still be one of the brightest objects in the sky. It will probably take on a beautiful brick-red hue as a result of light from the Sun being refracted onto the lunar surface by the Earth's atmosphere. This colour can change considerably after a volcanic eruption – in that case large amounts of dust in the atmosphere can make the Moon appear much darker. This time the southern lunar limb is much closer to the edge of the Earth’s shadow so will be appear much brighter than the northern edge of the Moon.

At 22.08 BST totality will end as the Moon begins to emerge from the umbra - the darkest part of the Earth's shadow - and then appears to brighten steadily. By 23.12 BST it will have left the umbra completely but keen-eyed observers may still see a yellow hue on the lunar surface – the result of the lighter penumbral terrestrial shadow. At 00.09 BST on 5 May the eclipse finally ends.

No special equipment is needed to watch a lunar eclipse and the unaided eye often has the best view, particularly when the Moon is near the horizon. Unlike solar eclipses, they are completely safe to observe – although it may be worth wearing warm clothing to prepare for a cool spring evening.

You can find a detailed guide to this and other eclipses on the NASA/GSFC eclipse homepage.