View at EarthSky Community Photos. | Radu Anghel captured this image from Bacau, Romania, on April 27, 2023. Radu wrote: “X and V from tonight’s moon.” Thank you, Radu! Learn how to see Lunar X and V below.
First quarter moon falls at 21:20 UTC on April 27, 2023
Lunar X and Lunar V
Have you heard of Lunar X and Lunar V? They are famous optical features on the moon, visible through telescopes. So when the moon’s terminator – or line between light and dark on the moon – is located in just the right place, you can see a letter X and a letter V on the moon’s surface. A sign of an alien visitation? No. Lunar X is a great example of how lighting and topography can combine on a planet or moon to produce a pattern that seems familiar to the human eye.
In reality, the illusion of Lunar X is created by sunlight falling on the rims/ridges between the craters La Caille, Blanchini, and Purbach. The V is caused by light illuminating crater Ukert, along with several smaller craters.
View at EarthSky Community Photos. | Kannan A in Singapore wrote on April 19, 2021: “Upon a close look at the moon tonight, I realized that the Lunar X and V were clearly visible. These are transient lunar features visible on the lunar surface for about 4 hours, once a month. They are most striking when they are visible on the shadow side of the terminator. But they will remain visible against the lunar surface even after the terminator has moved because they are brighter than the surrounding area.” Thank you, Kannan!View at EarthSky Community Photos. | Muhammad Dzarfan bin Muhammad Khairin was at Telok Kemang Observatory, Port Dickson Malaysia, when he caught both Lunar X and Lunar X on the moon on April 19, 2021. Thank you, Muhammad!
Basically, people see Lunar X and Lunar V at each cycle of the moon, but only for a short time. In fact, they’re observable for about four hours around the 1st quarter moon phase.
Bottom line: Lunar X and Lunar V are optical features on the moon, visible through a telescope for several hours around the time of the 1st quarter moon.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Prior to that, she had worked for the University of Texas McDonald Observatory since 1976, and created and produced their Star Date radio series. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. In 2020, she won the Education Prize from the American Astronomical Society, the largest organization of professional astronomers in North America. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.
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