Lunar Eclipse: Monday 21st January

Fancy an early morning start this coming Monday? Well, it's the only way that you're going to see the last total supermoon lunar eclipse visible in the UK for a while! The Moon will be visible as a Blood Moon (an orange/red hue) from 04:40 GMT, entering the mid-eclipse at 05:12 GMT and ending at 05:43 GMT. If you haven't seen one, it's a truly spectacular sight. If you have seen one, you know it's a truly spectacular sight and will want to see it again! 

It's completely fine to just use the naked eye to watch the event, but using binoculars or a small telescope to get a close up will also most definitely work. We do recommend wrapping up warm with a hot drink on these frosty mornings, so stay warm and enjoy a beautiful view (please clouds, give us this one)!


What is a blood moon? Why is it dark orange? 

2018 blood moon by Guiseppe Donatiello
Blood Moon in 2018.
Credit: Guiseppe Donatiello


A blood moon occurs when there is a lunar eclipse; when you can draw a straight line right through the Moon, Earth and Sun. This sort of event happens so rarely because the orbit of the Moon around the Earth is on a slightly tilted plane compared to that of the Earth and the Sun, so it's not a 2D plane that we're dealing with but in fact 3D. It doesn't happen often that the Moon is directly behind the Earth with the Sun on the other side .

What causes the colour?

A blood moon only ever happens when there is a Full Moon with the Earth sat in between it and the Sun. The Sun's light hits the far side of the Earth (the side that is experiencing daytime (which is also the reason why not everyone on the planet can see a blood moon at the same time)) and the shadow of the Earth is cast onto the Moon. The Earth is much larger than the Moon, so how is any light getting to the Moon at all? 

The answer: Rayleigh Scattering.

When photons from the Sun hit Earth's atmosphere, the blue light is scattered more than the red light emitted by the Sun; the blue light is scattered across the sky during the day. When the Sun also sets there is more atmosphere for all of the light to travel through and the blue light scatters even more intensely....leaving an abundance of red light in the sky. The process of light of different wavelengths (or colours) scattering more intensely than others is called Rayleigh Scattering. 

The same thing happens with a blood moon: the blue light scatters of the atmosphere in random directions because of the particular elements that make up our atmosphere, whilst more red light is then left and is refracted around the Earth's atmosphere and directed at the Moon! This why during a full lunar eclipse the Moon appears orange/red - the angle of refraction is far less for the red light when passing through our atmosphere. 



blood moon explanation: rayleigh scattering
Diagram of how the different light is scattered/refracted in Earth's atmosphere.
Source: Eggishorn


If you get up early enough, we hope you have clear skies and enjoy the view!