Bold claim: witnessing a selenelion is like spotting a cosmic illusion where the sun and a lunar eclipse share the sky at once. And yes, this is the part most people miss. A selenelion is a rare celestial event that occurs when both the sun and a lunar eclipse are visible simultaneously in the sky.
During a total lunar eclipse, Earth lies directly between the sun and the moon. Logically, you’d expect the sun to have already set by the time the eclipsed moon rises. Yet in a selenelion, observers can catch a fleeting moment where the sun sits low on one horizon while the eclipsed moon glows above the opposite horizon.
The name selenelion (occasionally spelled selenehelion) comes from French-influenced roots rooted in ancient Greek: selene meaning moon and helion meaning sun.
This seemingly impossible sight is made possible by the refraction of sunlight in Earth’s atmosphere. As light passes through and bends, or refracts, the sun’s rays allow both bodies to appear on the horizon at the same time, even though geometrically one should be out of view. The result is a dramatic image: a reddish “blood moon” rising while the sun glows on the far side of the sky.
Selenelions are rare and only visible from certain locations where the timing of moonrise or moonset lines up perfectly with the peak of a lunar eclipse. It’s a special treat for skywatchers who manage to glimpse it.
Jennifer Gray (https://weather.com/bios/jennifer-gray) is a weather and climate writer for weather.com. She has spent the past two decades covering major weather and climate events around the world.
