Once in a Super Red and Blue Moon!

Red or blue?

Its an important question here in Manchester*, and the answer can never be both!

However it seems if you’re the Moon you can be red and blue at the same time! But I don’t think that results in a purple Moon!

Tomorrow, 31st January 2018, there will be a Blue Moon and, in parts of the world there will also be a Blood (red) Moon.

A Blue Moon isn't actually blue! The phrase refers to a second new Moon in one calendar month. This photo was taken using a blue filter!

A Blue Moon isn’t actually blue! The phrase refers to a second new Moon in one calendar month. This photo was taken using a blue filter! Image credit: NASA/Kostian Iftica

A Blue Moon is a name used for a second full Moon in a calendar month. The Moon doesn’t actually look blue! There was a full Moon on 2nd January, so this one tomorrow is the second in January.

There are about 29 days between full Moons; most months are 30 or 31 days, so it is possible to get a full Moon at the very beginning and very end of a month. But it doesn’t happen very often, we don’t often get two full Moons in one month, hence the phrase “once in a Blue Moon” to refer to things that don’t happen very often.

There will be another Blue Moon in March, with full Moons on 2nd and 31st March – which perhaps makes them seem not so rare after all! But after that, there won’t be two full Moons in one calendar month until October 2020.

And at the same time, there will be a lunar eclipse visible in parts of the world on 31st January – eastern Europe, eastern Africa, Asia, Australia, the Pacific Ocean and North America. There’s info here about when it is visible in different places, you can search for your location on the Eclipse Map to find local times of the eclipse. Sadly it won’t be visible here in the UK.

The Moon actually does look red during an eclipse. This image is from a total lunar eclipse on October 27, 2004. Image credit: NASA

The Moon actually does look red during an eclipse. This image is from a total lunar eclipse on 27th October 2004. Image credit: NASA

A lunar eclipse makes the Moon appear red, and it is often referred to as a Blood Moon.

During a lunar eclipse the Earth is between the Sun and Moon, so the Moon is in the Earth’s shadow and light from the Sun cannot reach it directly. However it doesn’t disappear completely in Earth’s shadow, some light reaches the Moon by passing through Earth’s atmosphere. But as the light passes through Earth’s atmosphere it gets scattered – the blue light gets scattered more than the red and gets lost, and only the red light reaches the moon, hence the moon appears red and the name Blood Moon.

And to top things off, it will also be a Super Moon, meaning it will appear larger and brighter than normal (I don’t know what colour super is, I chose green!). The Moon’s orbit around Earth isn’t quite a perfect circle, it is more elliptical, so sometimes it is a bit closer to Earth and sometimes it is a bit further away. When it is closer it look a bit bigger – that’s a Super Moon.

So all in all, tomorrow is quite a day for the little ol’ Moon!

If you have a favourite colour for the Moon, or can think of a better colour than green for a Super Moon, do let us know…

* For the uninitiated, in Manchester this question usually refers to which football team you support. Red is Manchester United (yey!), blue is Manchester City (boo!).

About Sarah Crowther

I'm a Post Doc in the Isotope Geochemistry and Cosmochemistry group. I study xenon isotope ratios using the RELAX mass spectrometer, to try to learn more about the origins and evolution of our solar system. I look at a wide range of samples from solar wind returned by NASA's Genesis mission to zircons (some of the oldest known terrestrial rocks), from meteorites to presolar grains.
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