Why is the moon so red? Tonight's blood moon lunar eclipse explained

As soon as the moon rises from behind the horizon, it will be darker and redder than usual

If you're out tonight, look up: you might catch sight of the blood moon, and some other sights besides.

Unless the rain is ruining it, the UK is preparing for a lunar eclipse, during which the moon will turn a deep, bloody red and go much darker than usual.

And this one is extra special, marking a potentially once-in-a-lifetime experience: there won't be a lunar eclipse this long this century.

But why does the moon look so strange and red? It's all about light and location.

Why does it happen?

A eclipse happens when the Earth, Sun and Moon get in a line. In a lunar one, the Earth is in the middle – it sits between the Moon and the Sun and stops light getting between them.

The bloodiness comes as what light does get to the Moon makes its way around the Earth. As it does so, it is scattered, so that the longer wavelengths make it past the Earth and so are a deeper red.

It also means that the moon is much darker, because less light is getting to it.

When will it happen?

When the moon rises over the UK – at about 9pm – the lunar eclipse should be visible. But you might want to wait another hour or so until the sun has fully set and the sky is darker, which will allow you to see more of the dim disc of the moon.

Why is it called a 'blood moon'?

Because it's red, and looks faintly gory. There's nothing more to it than that.

But the name does appear to have encouraged the kinds of people – mostly British newspapers and YouTubers who identify themselves as pastors – who like to trick others into believing that there is something sinister or dangerous about the lunar eclipse. For that reason, some suggest the name should be dropped.