The truth about this rare super-blue-blood-Moon eclipse

Much excitement is being expressed in some social and traditional media about an upcoming lunar event that is being called a super-blue-blood-Moon eclipse.

The Moon glows red in a total lunar eclipse. Image credit: Paul Sutherland

This “incredibly rare” happening takes place on January 31st, 2018. But what is the truth behind the hype? We will try to explain, and also tell you how, and where you have to be, to see it.

Well the fact is that no individual part of this occurrence is particularly unusual. It is interesting that they coincide, but it will really appear no more special than any other total eclipse of the Moon.

The most remarkable part of the event will be the eclipse, because a total lunar eclipse is always a spectacular thing to witness. It is unlike an eclipse of the Sun, where the Moon blots out our local star, and happens when the Moon passes through the shadow that the Earth casts in space.

The eclipse explains the “blood” part of the description, because lunar eclipses have been labelled “blood moons” by some religious groups, presumably because the Moon looks red in the deepest part of the Earth’s shadow.

The “super” part of the label comes because the Full Moon when the eclipse occurs (and lunar eclipses can only ever happen at a Full Moon) will lie near its closest point in its elliptical orbit around the Earth. This means it will appear marginally larger in the sky, though to be honest, the difference is not enough to be noticed by any casual observer.

Related: Observing the Moon: 50 fantastic features

So why a “blue” Moon? Well that is because the Full Moon of January 31st will be the second of the month. There was also a Full Moon on January 1st. The second Full Moon in a month is known as a “blue Moon”.

Again that is interesting, but only because it is the Full phase that is repeated. The Moon repeats its appearance every month because it take about 29.5 days to progress from one phase to a repeat of it during its orbit.

If you think about it, that is a shorter timescale than the length of any month, so whatever phase the Moon shows on the first day must be repeated before the month’s end.

A representation of how the Moon moves through the shadow of the Earth. P1 marks the start of the penumbral eclipse, U1 the start of the drker umbral eclipse, U2 the start of totality, U3 the end of totality, U4 the end of the umbral eclipse, and P4 the time the Moon completely leaves the penumbra.

Sadly, none of the “super-blue-blood-Moon-eclipse” will be visible from the UK, Ireland, western Europe and western Africa. It can be seen, weather permitting, of course, across Australia, New Zealand, the Pacific, the Far East, and Alaska and north-western North America.

The rest of North America will see some of the eclipse as the Moon is setting. Eastern Africa and Asia will see parts during moonrise.

The Moon will enter the Earth’s pale outer shadow, the penumbra, at 10.51 UT (P1 in our diagram), and the dark inner shadow, the umbra, at 11.48 UT (U1). Totality lasts from 12.52 UT (U2 in the diagram) to 14.08 UT (U3).

The Moon will then slowly begin to exit the outer penumbra again (U4), being fully illuminated once more by 16.08 UT (P4). Read more about lunar eclipses in our guide: What is an eclipse of the Moon?

Related: What’s in the sky this month?

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