Once in a super blue blood moon? Three lunar phenomena overlap | Science| In-depth reporting on science and technology | DW | 31.01.2018
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Once in a super blue blood moon? Three lunar phenomena overlap

On January 31, for the first time in just over 34 years — or 152 years, depending where you live — a super moon, a blue moon and a blood moon all occured on the same night.

To be fair, it does sound pretty special: a celestial trifecta, a hat-trick in the sky, a three-moon extravaganza. That it is a thing to behold is confirmed by its rarity. The last time anyone on Earth witnessed this particular convergence was on December 30, 1983 but for most places the wait has been even longer, all the way back to 1866.

Unfortunately, most people living in Europe — including almost everyone living in Germany — missed out on the full spectacle. It's all a question of latitude you see, for when the moon rose over that part of the planet, the darkness of the eclipse had receded, meaning no blood moon was visible there. The blue and super bits still applied, at least.

For those living in North America, most of Russia, Asia, Australasia and parts of the Middle East, the odds of enjoying the full deck were a lot better.

Infografik Mondfinsternis 31. Januar 2018 ENG

So what exactly did those who live in the right places see with the spectacular-sounding super blue blood moon?

First of all, a super moon occurs when the moon is unusually close to Earth, making it appear much bigger and brighter to observers on our planet. This happens a few times a year and especially so during the winter months. Carolin Liefke, of the Association of German Star Friends (VdS) told dpa that during a so-called supermoon, the moon is 40,000 kilometers (24,854 miles) closer to the Earth than normal.

So what about the blue moon part? We all know the phrase "once in a blue moon", meaning something extremely rare, but will the moon actually be blue? Don't be too disappointed if it doesn't seem so to you.

A blue moon is the name given when a second full moon occurs in the space of a calendar month. Yet it does not appear to be especially blue and is more of a calendar event than something the naked eye will see. There was a full moon on January 2 and now another one on January 31, giving us the "blue moon".

"We have a full moon every 29 days, so this is something that can often happen," says Liefke. On average, a blue moon occurs once every two and a half years.

Last but certainly not least is the blood moon, which is a natural consequence of a total lunar eclipse.

The eclipse happens when the Earth passes, briefly, between the moon and the sun. The effect of this brief shadowing is that the moon appears to be blood-red, rather than its normal reflective bright color, as a result of the refraction of sunlight.

Viewers in the right location witnessed this total lunar eclipse. If you lived in North America, the eclipse was visible before sunrise on January 31. For those in the Middle East, Asia, eastern Russia, Australia and New Zealand, the full super blue blood moon could be seen as the moon rose on January 31.

There is some good news for Europeans who missed out on the lunar trifecta, at least: there is another total lunar eclipse coming on July 27 and that, unlike the January 31 instalment, will be visible from most parts of Europe.

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