Lunar ‘X’ Shadow Phenomenon Visible in China on June 22

Chinese skywatchers will have a rare opportunity on June 22 to observe the striking “Lunar X” phenomenon — a distinctive ‘X’-shaped shadow pattern that appears on the Moon’s surface for approximately two hours. According to Xinhua News Agency, this marks the second favorable observation opportunity for China in 2026, following a previous occurrence on April 24.

What Is the Lunar X?

The Lunar X — also known as the Werner X, named after the Werner crater on the Moon — is a clair-obscur (light-and-shadow) optical effect on the lunar surface. It appears only during the first quarter phase of the Moon, when sunlight strikes the lunar surface at a low, parallel angle along the terminator — the boundary between the Moon’s day and night hemispheres.

Liu Zhongli (刘仲利), a member of the Chinese Astronomical Society and astronomy educator at the Tianjin Science and Technology Museum, explained the phenomenon to Xinhua: “The ‘Lunar X’ is a visual light-and-shadow phenomenon produced by sunlight striking the Moon, appearing only during the first quarter phase. The peaks of certain craters are lit up while mountain shadows interweave, combining at the light-dark boundary to form the outline of the English letter ‘X’.”

The Science Behind the Illusion

The ‘X’ shape is formed by the illuminated rims of three specific craters — Blanchinus, La Caille, and Purbach — located in the rugged south-central highlands of the Moon. As described by Wikipedia, the X is visible only for a few hours before the first quarter, slightly below the lunar terminator. The elevated rims of these craters catch the sunlight while the lower terrain between them remains in shadow, creating the distinctive letter shape.

Viewing Details for June 22

The observation window runs from 17:10 to 19:30 Beijing time, with peak visibility at 18:10. Liu Zhongli noted that during this period, the sun has not yet fully set, creating brighter sky conditions. “Interested members of the public with the right equipment can use astronomical telescopes with an aperture of 8cm or larger to observe the lunar surface,” he said. “The ‘X’-shaped light pattern is located at the mid-southern portion of the lunar terminator.”

The XVL Triple Set

For those with keen eyes and proper equipment, the Lunar X is not the only spectacle on offer. Alongside the ‘X’, observers may also spot the Lunar V — formed by the Ukert crater and several smaller craters — and the Lunar L, a less commonly discussed ‘L’-shaped shadow pattern. Liu Zhongli encouraged enthusiasts to “carefully search up and down along the lunar terminator for the opportunity to simultaneously find the ‘Lunar V’ and ‘Lunar L’, collecting the ‘XVL triple set’ all at once.”

A Growing Interest in Astronomy

China has invested heavily in space exploration in recent years, including the Chang’e lunar exploration program, the Tiangong space station, and the FAST radio telescope. Public interest in astronomy has grown correspondingly. Events like the Lunar X phenomenon serve as accessible entry points for amateur astronomers and help maintain public enthusiasm for space science.

The Lunar X occurs every synodic month (approximately 29.5 days), but its visibility from any given location is limited. It may appear at any time of day, and when it occurs during daylight hours, observation becomes significantly more difficult. The June 22 event is particularly favorable because the peak at 18:10 Beijing time falls in early evening, making it accessible after work or school hours, and summer skies generally offer better weather conditions for observation across much of China.

What to Watch For

Amateur astronomers across China are advised to prepare telescopes with at least 8cm aperture and find locations with clear skies and minimal light pollution. Weather conditions on June 22 will significantly impact visibility across different regions. As noted by the China Internet Information Center, the phenomenon has been photographed multiple times from locations across China, including Beijing, Jiangsu, and Tianjin, demonstrating its accessibility to dedicated observers.

While scientifically well-understood, the Lunar X continues to captivate observers — a reminder that even familiar celestial neighbors can still surprise us when light and shadow align just right.