The 'Lunar X' or 'Werner X' is an optical illusion formed by shadows on the moon's surface, visible during its first quarter phase. This phenomenon occurs every four hours, presenting a silhouette resembling an 'X' as sunlight interacts with lunar topography. To observe it, viewers should aim for the terminator line near the Werner crater around 8:20pm ET. Light pollution can obscure the view, making binoculars or telescopes beneficial for clarity. The 'X' will fade after an hour, offering a brief but striking visual for skywatchers in the US and Canada.
The X marking will be at peak visibility for about an hour and then slowly fade away as its surrounding gradually fill with light, according to David M.F. Chapman.
Getting away from sources of light pollution, such as buildings and streetlights, will also help the X stand out. But you will have to give your eyes time to adjust to the darkness.
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