After a week of political turmoil, here’s one good reason to be glad you’re living in the UK: in the very early hours of Monday morning, our divided kingdom will be one of the best places in the world to watch the next lunar eclipse.
Early-risers and late-night owls will start seeing the Earth’s shadow cover the Moon from 02:35 GMT all the way until the eclipse ends at 07:49 GMT.
While lunar eclipses are not a rare occurrence – they happen two or three times a year – the UK will be treated to an impressive show. As the entire eclipse happens before the Sun comes up, skywatchers will be able to enjoy it from start to finish; something that won’t happen again until 2029. The previous lunar eclipse, which happened last July, was already about half way through when night started falling in the UK, which means that the Moon had already almost reached its peak eclipse when it rose. This time, assuming the weather is clear, you should be able to watch all the different stages of the process.
What is so special about a lunar eclipse anyway?
A lunar eclipse happens when the Sun, Earth and Moon align. In reality, that happens every month or so; every time we get a full Moon, to be precise. Lunar eclipses, however, happen when this alignment coincides with the Moon going through the Earth’s shadow.
“A way to picture it is to think of the Earth’s shadow as a cone projected into space,” says Chris North, a science lecturer at Cardiff University. “A full Moon will be roughly opposite the Sun in the sky, which is why we can see it fully lit; but it will be slightly above or below the cone.”
In contrast, during a lunar eclipse, the Moon finds itself going through the cone of the Earth’s shadow. And because the Moon doesn’t emit light, but reflects the Sun’s rays, it becomes darker – at least when seen from our planet.
Of course, the Moon orbits around the Earth, which means that an eclipse is a gradual process: the Moon becomes darker as it creeps deeper into the Earth’s shadow. In its cone of shadow, the peripheries, where the shadow is weaker, are called the penumbra; and the centre of the cone, where the shadow is the deepest, is the umbra.
So what can you expect?
The eclipse starts when the Moon enters the penumbra. At that stage, which on Monday will happen at 02.35 GMT, the Earth isn’t yet blocking the whole of the Sun, so the Moon still gets lots of sunshine – observers will only notice that it darkens slightly.
The real show will kick off at 03:33 GMT, when the Moon enters the umbra: that’s when and where the Earth’s core shadow starts taking over. You should see a black wedge munching the Moon away and growing bigger.
While the Moon is still partly in the penumbra and partly in the umbra, the eclipse is called partial – and indeed the Moon is still partially lit. The total eclipse starts when it has completely entered the umbra. If it’s peak eclipse that you are after, set your alarm at 04:41 GMT.
Last July’s lunar eclipse was the longest total eclipse of the century, lasting one hour and 43 minutes. This year, the Moon will start leaving the umbra just over an hour after it has fully entered it – at 05:43 GMT – and will have exited the penumbra at 07:49 GMT.
What’s with the red moon hype?
In theory, once the Moon is completely within the Earth’s shadow, it should be completely dark, and therefore invisible, right? Well, not exactly. Once the Moon is in the umbra, the Earth’s atmosphere still acts as a lense that refracts the Sun’s light and “fills in” the Moon. Molecules in the Earth’s atmosphere scatter the Sun’s blue light, while bending its red lights and therefore letting them travel all the way to the Moon. This is the same phenomenon, in fact, that explains why we get red sunsets.
In the case of a lunar eclipse, it means that while the Moon is in the Earth’s core shadow – this time, between 04:41 and 05:43 GMT – it will appear red. But which kind of red? Well, we won’t know until it happens as the Moon’s colour will depend on the Earth’s atmospheric conditions. “Typically, volcanic eruptions can make the Moon look more red because of the dust particles they bring into the atmosphere,” says North. “We had the Anak Krakatau eruption a few months ago, so maybe that will have some sort of effect.”
How can you get an Instagram-worthy shot?
A red Moon looks good on a social media feed, but since its very nature is lack of sunlight, it may prove to be a photographic challenge. Use multiple exposures to compensate for the lack of light, and make sure you have a tripod to stabilise your pictures, especially if you’re using a telephoto lens with a long focal length.
The partial eclipse may prove to be an interesting subject to photograph, too. To the naked eye, it will look like the Moon is divided between a pit-black wedge and a bright white side. North explains that in reality, the darker side will already be reddening, but the contrast between the two sides is too sharp to let us see it. “You can pull it out with photos,” he says, “although the imbalance in brightness is so big that you would have to hugely overexpose the lit bit of the Moon to see any red.” And if you have only come with your eyes, you will have to wait until the Moon has fully entered the umbra to see it turn red.
What if you miss it?
Lunar eclipses are fairly regular, and your next opportunity to watch one will be on July 16 – although it will be a partial one, which is arguably of less interest. In any case, there’s no reason to get FOMO: if there is one thing that lunar eclipses do well, it’s predictability. So make sure you keep an eye on NASA’s table of future eclipses for the rest of the century.
This article was originally published by WIRED UK
