What are Anticrepuscular Rays?

Anticrepuscular rays. Image credit: Dan Acosta

If there was no atmosphere the daytime sky would like the nighttime one, but with a fiercely bright star where the sun was.

Air is transparent, but it influences all light that passes through it. The atmosphere is responsible for blue skies as well as clouds.

One of the less well known effects of the atmosphere is the way it reflects light.

If we look east at sunrise or west at sunset, the low sun makes horizon is very bright of course. But it is also quite bright in the opposite direction too. The light from the low sun passes us and bounces back from the air in the opposite direction.

Crepuscular rays form when the sun is just below the horizon or low clouds. The dark lines are shadows formed by clouds.

Anticrepuscular rays form directly opposite the sun at similar times. The reflected light and consequent effect is weaker, but still beautiful.

The centre of crepuscular rays is the sun and the centre of anticrepuscular rays is the ‘antisolar point’, the spot in the sky directly opposite the sun.

Clouds form shadows in the air over Indian Ocean
Crepuscular rays seen from Brighton beach, Sussex.

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