Massive 'X' and 'V' shapes will appear on the moon tonight — here's how to see them

A trick of the light will make a colossal "X" and "V" appear on the moon overnight on May 23-24, as sunlight catches broken crater rims along the line separating night from day. Here's how and when to find the striking "clair-obscur" effect.

The face of the moon never looks the same from one night to the next, as the shifting angle between the moon and sun causes sunlight to sweep across its surface, altering the shadows cast by craters, mountain ranges and ravines.

Our brains are predisposed to find familiar shapes in the heavily cratered lunar landscape, giving rise to so-called "clair-obscur" effects — a name derived from a French word for light (clair) and another for shadow (obscur).

When to see the lunar "X" and "V"

The "X" and "V" will be visible on the lunar surface around the moon's first quarter phase on May 23, as the lunar disk appears with its right half lit by direct sunlight and its left hidden behind a veil of shadow.

Both clair-obscur effects will be at their most visible from 6 p.m. EDT (2200 GMT) on May 23 through the early hours of May 24, as they appear close to the line separating lunar night from day, known as the terminator.

Where to find the "X" and "V" on the moon's surface

A small telescope or binoculars will allow you to spot the lunar "V" shining close to the terminator between the lunar seas of Sinus Medii and Mare Vaporum, approximately 10 degrees above the lunar equator. The letter-like shape marks where sunlight glances off the rim of the Ukart crater, along with other pieces of broken terrain and small impact sites.

Follow the terminator down to a point 25 degrees below the equator to find the lunar "X", which is formed from the broken rims of the Purbach, Blanchinus and La Caille impact sites. Be sure to check out our guide to photographing the moon, along with our roundups of the best cameras and lenses for astrophotography, if you want to snap your own image of the striking clair-obscur effects!

Editor's Note: If you would like to share your moon photography with Space.com's readers, then please send your photo(s), comments, and your name and location to [email protected].