Starwatch: red marvel that is a lunar eclipse

A total lunar eclipse will be visible over most of Europe, Asia, Australia and South America on 27 July. Only North America misses the show this time.

During a total lunar eclipse, the moon passes through the Earth’s shadow. Once totally immersed, it turns to a deep red colour. This glorious sight occurs because of the way sunlight bends (refracts) through the Earth’s atmosphere.

The blue component of sunlight is scattered all over, which is why the sky looks blue to us, but the red light is refracted, which directs it behind the Earth and onto the Moon.

The eclipse starts before the moon rises in the UK. This means that Earth’s shadow will already be crossing the lunar surface when the moon climbs above the south-eastern horizon about 8:50pm. Half an hour later, the moon will be at the midpoint of the eclipse and it will turn red. By 10:15pm, it will be leaving Earth’s shadow.