Blood moon: The science behind it

A spectacular red moon rose on Friday evening, marking the beginning of the longest total lunar eclipse of the century.

But unfortunately it was not visible for much of the UK due to cloud cover.

:: What is a "blood moon"?

To give the blood moon its technical name, it is a lunar eclipse – caused by the Earth passing between the moon and the sun.

During a total eclipse, the Earth completely obscures sunlight from directly hitting the moon as the sun, the Earth and the moon will be in perfect alignment.

Image: The blood moon was not visible for much of the UK

Only light that is refracted through Earth's atmosphere manages to reach the moon, with everything outside of the red wavelengths being scattered, leaving the moon looking blood red.

Because of the way the moon orbits the Earth, and because the Earth orbits the sun, there are always at least two lunar eclipses every year.

However, there are rarely total eclipses, when both the moon is full and the Earth completely blocks the sun.

The Earth will pass between the sun and the moon for 103 minutes. 0:46
Video: What is a blood moon?

:: When did the blood moon happen and was it visible?

The Earth passed between the sun and the moon for 103 minutes on Friday evening.

The eclipse was visible in its entirety for people located around the Indian Ocean and surrounding countries, from India to the Democratic Republic of the Congo.

It was partially visible in the UK from 8.50pm on Friday evening toward the south east – but rain clouds and thunderstorms scuppered skygazers' attempts to watch the celestial spectacular.

LONDON, UNITED KINGDOM - JANUARY 31:  A supermoon rises behind St. Paul's Cathedral on January 31, 2018 in London, United Kingdom. The super blue blood moon is a rare combination of a supermoon, a blood moon and a blue moon all simultaneously occurring.  (Photo by Chris J Ratcliffe/Getty Images)
Image: Unlike a solar eclipse, a lunar eclipse is quite safe to look at with the naked eye

By the time the blood moon was rising on Friday evening in the UK, it had started to pass out of Earth's shadow, while remaining quite red.

The visibility of the lunar eclipse. Pic: Piruliton
Image: Where will the eclipse be visible? Pic: Piruliton

:: Is it safe to look at?

Unlike a solar eclipse, a lunar eclipse is quite safe to look at with the naked eye.

There will be other opportunities to see the phenomenon, with 230 expected this century – but Friday's will be the longest.

A "super blood blue moon" is seen during an eclipse, behind an office building in Hong Kong, China
Image: The Earth will pass between the sun and the moon for 103 minutes

:: Is it interesting to scientists?

Lunar eclipses often throw up interesting data for astronomers.

When the Earth passes in front of the moon, it rapidly causes its surface temperature to drop – causing lunar rocks to suddenly freeze and crack, releasing gas.

More from Science & Tech

Astronomers' telescopes aimed at the blood moon have seen this happening, as well as another mysterious phenomenon – seemingly random spots of heat, often concentrated around craters.

Although these heat spots have been studied for more than half a century, scientists have not yet managed to establish what is producing this heat.

Original Article

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