A special supermoon

By Kathrin Kobus

Photograph by Professor Antonio Martin-Carillo.

The new year began with a full moon, and the first month ended with a full moon as well. If there are two full moons in one calendar month, the second is called a ‘blue moon’.
What happened on the last day of January 2018 was different on a larger scale. It was a truly rare astronomical event.
It is known as a ‘Blue Blood Supermoon Eclipse’, the last of which occurred over 150 years ago! It is extremely unusual for this number of very rare lunar events to occur so near together and in such a short space of time.

During a total lunar eclipse, the Earth blocks all direct light from the sun from reaching the moon. Blue moons are also rare, happening once every two or three years (although – in another extraordinary turn – there will be a second blue moon this year in March for some parts of the world!) “It is so rare that this is where the phrase, ‘once in a blue moon’ comes from,” says Emma Callis, PHD Student at UCD School of Physics.
Adding to all the already special features is the fact that whoever had the chance to observe the moon might have been under the impression that it was much closer than usual.
It’s all just an optical illusion. “Due to the fact the moon’s orbit is elliptical, its distance from the Earth varies by roughly 12%, and during this event, the moon will be very close to its perigee, its closest approach to Earth. Therefore it will appear to be nearly 10% larger and 30% brighter than average, and this is known as a ‘supermoon’.”
The term supermoon is not an astronomical term per se. It was only introduced by astrologer Richard Nolle nearly forty years ago in 1979. So that’s ‘blue’ and ‘super’ cleared up. Why ‘blood moon’?

“The term ‘blood moon’ refers to the reddish tint the moon usually acquires during a total lunar eclipse. This happens for the same reason that the sky is blue, due to a process called Rayleigh scattering. The light that does reach the surface of the moon has travelled through the Earth’s atmosphere, where bluer wavelengths of light become scattered more than others, and therefore only the redder light goes straight through the atmosphere and on to the moon.”
It has nothing to do with werewolves and vampires on the prowl, whatsoever. This 31st of January, all things came together and made it a nightly event that doesn’t happen every year, or decade or century.

“This kind of event is so rare because the chance of a total lunar eclipse, a blue moon, and a supermoon all occurring at once is incredibly slim. While I can’t estimate the time of the next Blue Blood Supermoon, the next Blood Supermoon is 21st January 2019.
Until then we have to be contend with just the usual full moon every 29.5 days – ‘Sorry, Night.’