We’ve all seen crepuscular rays, or sunrays, converging on the sun. They appear as pillars of sunlight, all converging at a single point, streaming up from the horizon or down through gaps in clouds. Next time you see them … turn around.
If you look opposite the direction of the sun, you might catch a glimpse of elusive anticrepuscular rays. These rays appear to converge towards the antisolar point – that is, the point on the sky opposite the sun. If you want to see them, remember these three tips:
1. Look in the direction opposite the sun, next time you see crepuscular rays extending from the horizon.
2. Look carefully. Remember that anticrepuscular rays are fainter and more elusive than crepuscular rays.
3. Watch around sunrise or sunset for anticrepuscular rays. That’s when they are are most frequently visible.
Les Cowley of the great website Atmospheric Optics says:
Like crepuscular rays they are parallel shafts of sunlight from holes in the clouds and their apparently odd directions are a perspective effect. Think of a long straight road, it converges towards the horizon but turn around and it also converges to the opposite horizon. Crepuscular and anticrepuscular rays behave in the same way.
Anticrepuscular rays are not rare but they must be sought carefully. When ordinary crepuscular rays are visible, turn around and search for their opposite numbers.
Bottom line: If you want to see anticrepuscular rays – columns of sunlight, often with dark shadowed areas between the columns – look carefully opposite the direction of the sun. They are most often seen at sunrise or sunset.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.