Blood moon: Why this lunar eclipse is going to be so long

It's all explained by the movements of the moon

The blood moon would be reason enough to head out and look up at the sky. But this lunar eclipse is even more special: it will be the longest this century.

The sight will last for a full 103 minutes, making it even harder to miss than usual.

And the reason it is so long is similar to the reason it is happening in the first place: a neat coincidence in the way the Moon lines up with the Sun and the Earth.

A lunar eclipse happens when the Earth blocks out the light that would usually be reaching the moon. When it does, the passage of light past the Earth makes it go a deep red – and when that bounces back off the Moon and into our eyes, it turns it a deep, bloody red and gives the event its name.

This time around, that will be long because the moon passes right through the centre of the shadow of the Earth. As such, it takes longer to get through the darkness, and so the eclipse lasts longer.

As well as that, the Earth is about as far from the Sun as it gets during its orbit. That makes the journey longer, too, since the angle and the distance makes the shadow larger.

Normally, the eclipses take a more glancing path or a closer approach of the Earth. That means that other lunar eclipses – which are fairly regular – are usually slightly shorter, though only by a couple of minutes.

The length should mean that the impact of the thunderstorms that are forecast for Friday evening – and which threaten to spoil the event – should be less. Even if it is raining and covered in clouds for some part of the time, it's likely that you'll be able to spot something.

Spotting the eclipse should be relatively easy, since you only have to look up at the Moon. There's no special equipment required, like there is with a solar eclipse.

To view the eclipse, find a hill or flat area with few trees or buildings to the Southeast, as the Moon will be low in the sky throughout the eclipse," said Gregory Brown, astronomer at the Royal Observatory Greenwich. "A pair of binoculars or a small telescope can make the event all the more impressive, but there will still be plenty to see with just your eyes too!"