The lunar surface holds subtle, temporary wonders visible only under precise conditions. These aren’t permanent features but optical illusions created by sunlight interacting with crater rims during the moon’s first quarter phase. One lucky amateur astronomer captured this effect by chance a decade ago, and now, with the right timing and equipment, anyone can witness these fleeting shadows: the lunar X and V.
What are the Lunar X and V?
The lunar X and V aren’t physical markings but illusions formed when sunlight strikes specific craters at a sharp angle. The X appears due to light hitting the rims of La Caille, Blanchinus, and Purbach craters, creating a bright “X” shape. Similarly, the V is formed by light illuminating Ukert crater and nearby smaller craters. These illusions are transient, appearing only during the moon’s first quarter when the terminator (the line between light and shadow) aligns correctly.
Timing is Everything
These features appear only during a 4-to-6-hour window each month. The key is observing the moon at its first quarter phase. However, visibility varies significantly depending on your location.
- The next first quarter is on January 26th at around 5 AM GMT. But if you’re in the UK, the moon will be below the horizon then.
- From New York, the first quarter occurs around midnight on January 25th, making the X and V visible from approximately 10 PM to 2 AM.
- Sydney, Australia, will see the first quarter around 3 PM on January 26th —too much daylight for observation.
To maximize your chances, use astronomy software like Stellarium to pinpoint the best viewing times for your location. The next opportunities are on February 24th, March 25th (ideal for the UK at around 7 PM local time), and April 24th/25th.
Equipment and Preparation
While not strictly necessary, a telescope significantly enhances visibility. The real challenge lies in timing. The lunar X and V require a dark, clear night with the moon positioned high in the sky. Proper planning and location-specific timing are crucial.
The lunar X and V demonstrate how much beauty is hidden in plain sight, waiting for the right alignment of light, shadow, and observation.
To learn more, visit newscientist.com/maker.
