After a week of political turmoil, here's a good reason to be happy to live in the UK: in the 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 early risers will begin to see the shadow of the Earth cover the Moon from 02:35 GMT until the eclipse ends at 07:49 GMT.
Although lunar eclipses are not a rare occurrence – they happen two or three times a year – the UK will be treated with an impressive spectacle. As the entire eclipse occurs before the sun appears, the observers of the sky will be able to take advantage of it from beginning to end; something that will not happen again until 2029. The previous lunar eclipse, which happened last July, was already midnight when it began to fall in the UK, which means that the Moon had almost reached its peak of eclipse when it rose. This time, assuming the weather is clear, you can watch all the different stages of the process.
What is so special about a lunar eclipse?
A lunar eclipse happens when the Sun, the Earth and the Moon align. In fact, this happens more or less every month; Every time we have a full moon to be precise. Lunar eclipses, however, happen when this alignment coincides with the Moon passing through the shadow of the Earth.
"One way to imagine this is to think of the Earth's shadow as a cone projected into space," says Chris North, a professor of science at Cardiff University. "A full moon will be roughly opposite the sun in the sky, and that is why we can see it fully illuminated; but will be slightly above or below the cone. "
In contrast, during a lunar eclipse, the Moon is passing through the cone of the Earth's shadow. And since the Moon does not emit light, but reflects the rays of the Sun, it becomes darker – at least when viewed from our planet.
Of course, the Moon orbits the Earth, which means that an eclipse is a gradual process: the Moon becomes darker as it approaches the Earth's shadow. In its cone of shadow, the peripheries, where the shadow is weaker, are called penumbra; and the center of the cone, where the shadow is deeper, is the umbra.
so what can you expect?
The eclipse begins when the moon enters the penumbra. In this phase, which will take place at 02:35 GMT on Monday, Earth is not yet blocking the entire sun, so the moon is still getting a lot of sunshine – observers will only notice that it dims a bit.
The real show begins at 03:33 GMT, when the Moon enters the umbra: it is when and where the earth's central shadow begins to take over. You should see a black wedge chewing the moon and growing.
While the moon is still partially in the half-light and partially in the umbra, the eclipse is called partial – and indeed the moon is still partially illuminated. The total eclipse begins when it completely enters the umbra. If it is the peak of the eclipse you are looking for, set your alarm at 04:41 GMT.
The lunar eclipse of last July was the longest total eclipse of the century, lasting one hour and 43 minutes. This year, the Moon will begin to leave the umbra just over an hour after it has completely entered – at 05:43 GMT – and will be out of the gloom at 07:49 GMT.
What's with the red moon campaign?
In theory, once the Moon is completely within the shadow of the Earth, it must be completely dark and therefore invisible, right? Well, not exactly. When the Moon is in the umbra, the Earth's atmosphere still acts as a lens that refracts the Sun's light and "fills" the Moon. Molecules in Earth's atmosphere spread the blue light of the Sun as they curl their red lights, allow them to travel all the way to the Moon. This is the same phenomenon, in fact, which explains why we have the red sunset.
In the case of a lunar eclipse, it means that as long as the Moon is in the earth's central shadow – this time between 04:41 and 05:43 GMT – it will appear in red. But what kind of red? Well, we will not know until this happens, because the color of the Moon will depend on the atmospheric conditions of the Earth. "Normally, volcanic eruptions can make the moon look redder because of the dust particles they bring into the atmosphere," says North. "We had the eruption of Anak Krakatau a few months ago, so maybe it has some effect."
How can you get a picture worthy of Instagram?
A red moon looks good on a social media feed, but as its very nature is the lack of sunlight, it can be a photographic challenge. Use multiple exposures to compensate for the lack of light and make sure you have a tripod to stabilize your photos, especially if you are using a telephoto lens with a long focal length.
Partial eclipse can be an interesting subject to photograph as well. With the naked eye, it will appear that the Moon is divided between a black wedge and a bright white side. North explains that in reality the darker side will already be reddish, but the contrast between the two sides is too sharp to let us see. "You can take it with pictures," he says, "though the imbalance in brightness is so great that you would have to overexploit the illuminated part of the Moon to see any red." And if you just came with your eyes, you'll have to wait until the moon has completely entered the umbra to see it turn red.
What if you make a mistake?
Lunar eclipses are fairly regular, and your next opportunity to attend one will be on July 16 – although it is a partial opportunity, which is arguably of lesser interest. Anyway, there is no reason to get the FOMO: if there is one thing that lunar eclipses do well, it is predictability. So keep an eye on NASA's future eclipse chart for the rest of the century.
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