It might sound like an elaborate publicity stunt for Elon Musk‘s SpaceX.
But stargazers in the UK and the US will be able to see a giant X on the moon this week.
A rare event known as the Lunar X is set to take place on Thursday 6 March, during which a large X will appear briefly on the moon’s surface.
While you might be able to see it by squinting, experts advise using a pair of binoculars or a small telescope to get the best view.
The lunar display will be visible from 23:00 GMT (18:00 EST) and will last just four hours – so you’ll need to be quick if you want to catch it.
The Lunar X, also known as the Werner X, is a type of astronomical feature called a ‘clair-obscur’, meaning it is produced by a trick of the light.
Keen observers should also be able to spot another clair-obscur called the ‘Lunar V’ which forms at the same time.
Here’s how you can catch a glimpse of this fascinating lunar spectacle.
Skygazers will be able to see a huge ‘X’ and a ‘V’ light up the moon this Thursday in a rare lunar event. Pictured: The Lunar X and Lunar V seen from Malaysia in 2021
The Lunar X isn’t a real physical structure on the moon, but rather a pattern of light and shadow created at specific times in the lunar month.
The ‘X’ is formed at the point where four craters, Purbach, La Caille, Blanchinus and Regiomontanus, come close together in the moon’s rugged southern highlands.
As the moon orbits Earth, it moves in between us and the sun, so it looks as if more or less of the lunar satellite is being illuminated at any given time – this is why the moon has phases.
When we can only see part of the moon’s illuminated surface the line between the light side and the dark side is called the ‘terminator line’.
Every body that orbits the sun has a similar terminator line dividing its light and dark sides, which moves as the body rotates relative to the sun’s rays.
Just like during sunset on Earth, features on the moon’s surface look different when they are near the terminator line because the sun is so low on the horizon.
This means that small features cast long shadows which are easily visible from Earth, making craters and mountains much more apparent.
If you follow the terminator line to the north, you will find another famous clair-obscur effect called the Lunar V.
As the moon orbits the Earth different sections appear in shadow from our perspective, the line between the dark and light side is called the ‘terminator line’. The Lunar X can be found on this line during certain times of the month
Features on the terminator line (pictured) are clearly visible because the sun’s low angle casts long shadows across the lunar surface. This makes lunar dawn or sunset the ideal time to see many structures on the moon from Earth
Like the Lunar X, this forms as the low sun at lunar dawn catches on raised features near the crater Ukert, forming a distinctive ‘V’ shape
During the first quarter phase, the terminator line passes over the intersection of those four craters and the X appears to glow brightly.
Since these phenomena always form in the same place on the terminator line, they are fairly easy to spot if you know when and where to look.
To find the Lunar X on March 6, start looking at the moon from around 23:00 GMT (18:00 EST).
In the UK, the moon will set at 02:00 in the morning of March 7 so it will appear fairly low on the horizon.
To ensure you have a good view, try to find a spot that has an unobstructed line of sight to the horizon without any trees or buildings blocking the way.
Getting away from sources of light pollution, such as cars and streetlights, and giving your eyes time to adjust to the darkness will also make the X easier to spot.
Start looking about a third of the way up the terminator line from the southern edge of the moon.
When the sun is low on the horizon it picks out raised structures formed by a cluster of craters which are illuminated brightly. These will be visible in the UK from about 23:00 GMT (18:00 EST) for a period of four hours
The X won’t form immediately, instead appearing slowly over a period of roughly 2.3 hours.
After forming, the X will be visible for another hour before fading over approximately 70 minutes as the sun rises completely and the effect is lost.
David Chapman, a retired astronomer from the Halifax Centre of the Royal Astronomical Society of Canada, wrote in an article: ‘One has a very good chance of seeing the X as a dazzling sunlit feature suspended in inky shadow, completely independent of the terminator boundary.’
During that time, you should be able to find the ‘V’ by simply following the terminator line to the north until you see the bright, glowing structure.
Although these are technically visible to the naked eye under perfect conditions, using a good pair of binoculars or a small telescope is recommended to see them clearly.
However, you won’t need anything particularly powerful as a weaker magnification is actually preferable.
Mr Chapman writes: ‘All this can be seen at high magnification; however, for the best “X” effect, lower magnification is best.’
Unfortunately, the viewing conditions in the UK will not be ideal, as the weather forecasts suggest clear skies are unlikely.
The weather in the UK will not be ideal this Thursday evening with heavy cloud cover (left) and some rain (right) forecast over most of the country
According to the Met Office forecast, by midnight on Thursday, much of the UK will be blanketed in clouds with some small gaps emerging throughout the evening in the east.
Rain is also expected over most of the Southwest of England, Wales, and Scotland throughout the evening.
But if you don’t get the chance to see the Lunar X this week, there is no need to worry.
Since this effect is created by the lunar dawn, it actually appears once every single month.
The only issue is that the moon is not always visible for the few hours in which the X and V can be seen so there are usually between one and five good opportunities per year.
Your next chance to see the Lunar X from the UK will be on the morning of April 5 from 13:00 GMT (08:00 EST).
While this will be during the day, the Lunar X is actually so bright that it can be spotted with binoculars even during the daytime if you know where to look.
After that, the Lunar X and Lunar V won’t be visible at night until July 3 later this year.
The phases of the moon
Like Earth, the Moon has a day side and a night side, which change as the Moon rotates.
The Sun always illuminates half of the Moon while the other half remains dark, but how much we are able to see of that illuminated half changes as the Moon travels through its orbit.
In the Northern Hemisphere, the phases of the moon are:
1. New Moon
This is the invisible phase of the Moon, with the illuminated side of the Moon facing the Sun and the night side facing Earth.
2. Waxing crescent
This silver sliver of a Moon occurs when the illuminated half of the Moon faces mostly away from Earth, with only a tiny portion visible to us from our planet.
3. First Quarter
The Moon is now a quarter of the way through its monthly journey and you see half of its illuminated side.
4. Waxing Gibbous
Now most of the Moon’s dayside has come into view, and the Moon appears brighter in the sky.
5. Full Moon
This is as close as we come to seeing the Sun’s illumination of the entire day side of the Moon.
6. Waning Gibbous
As the Moon begins its journey back toward the Sun, the opposite side of the Moon now reflects the Moon’s light.
7. Last Quarter
The Moon looks like it’s half illuminated from the perspective of Earth, but really you’re seeing half of the half of the Moon that’s illuminated by the Sun ― or a quarter.
8. Waning Crescent
The Moon is nearly back to the point in its orbit where its dayside directly faces the Sun, and all that we see from our perspective is a thin curve.
