If you’ve ever wanted to see something straight out of a sci-fi movie, your chance will be coming soon. That’s because this week, a massive ‘X’ is set to appear on the Moon.
On Thursday, March 6, a rare phenomenon known as the Lunar X will be visible for a few short hours, offering a stunning spectacle for stargazers in the UK and US.
While it’s easy to think that this is more of an elaborate Elon Musk marketing stunt for SpaceX, it’s actually the work of the "clair-obscur" effect, a trick of the light caused by the sun casting shadows on the Moon’s rugged surface.
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The illusion forms at the meeting point of four craters; Purbach, La Caille, Blanchinus, and Regiomontanus; as the light hits them at just the right angle. The result? A giant glowing ‘X’ appearing on the lunar surface for a brief period.
And if you’re paying attention, you might also spot another similar effect — the Lunar V — which forms in the same way near the crater Ukert.
The Lunar X will begin forming at around 11:00 p.m Greenwich Mean Time and 06:00 p.m Eastern Standard Time, lasting for approximately four hours. The ‘X’ won’t appear all at once — it will gradually come into view over 2.3 hours, shine brightly for about an hour, and then fade away over the next 70 minutes as the sunlight shifts.
In the UK, the Moon will set around 02:00 p.m Greenwich Mean Time on Friday, March 7, meaning you’ll want to find a clear spot with an unobstructed view of the horizon. Those in the US will have a better chance of seeing it higher in the sky, due to it being 09:00 a.m. Eastern Standard Time at that point.
Using binoculars for stargazing (Getty Images)
How to see the Lunar X
If you’re keen to check out the giant X on the Moon and Lunar V for yourself, you certainly can do. However, while they will technically be visible to the naked eye, you’ll need to keep a couple of things in mind — along with grabbing a pair of binoculars or a small telescope to get the best view.
When looking at the Moon around the given time, you’ll need to look for the terminator line — the boundary between the light and dark sides of the Moon. Next, move about a third of the way up from the southern edge, and you should spot the ‘X’ taking shape.
Finally, follow the terminator line north, and you’ll also see the Lunar V.
According to retired astronomer David Chapman, the best way to view the Lunar X is at lower magnification, as this enhances the glowing effect.
The downside for many hopefuls in the UK, is that they might be out of luck due to cloudy skies being expected over much of the country — especially in the southwest, Wales, and Scotland. The best chance for clear skies in the United Kingdom to see this natural event will be for those in the east.
Thankfully, this won’t be the only chance people will get to to see the Lunar X. The phenomenon actually happens been one and five times a year, though it’s not always visible. The next chances will occur on Saturday, April 5 (01:00 p.m GMT and 08:00 p.m EST) and July 3.
So, if the weather plays nice, grab your binoculars, head somewhere dark, and witness one of the Moon’s most fascinating optical illusions before it disappears.