Atmospheric Refraction
Calculate how much the Earth's atmosphere bends the light of stars and planets based on their altitude.
0° = Horizon, 90° = Overhead (Zenith).
arcminutes
Why Light Bends
As light from a star enters Earth's atmosphere, it passes from the vacuum of space into increasingly dense air. This causes the light to bend (refract), making celestial objects appear slightly higher in the sky than they actually are.
Horizon Effects
Refraction is strongest at the horizon, where light must travel through the thickest part of the atmosphere. At the horizon, refraction is about 34 arcminutes (slightly more than the diameter of the full moon). This means when you see the Sun touching the horizon, it has actually already set!
Frequently Asked Questions (FAQ)
Does temperature affect refraction?
Yes. Cold, high-pressure air is denser and refracts light more than warm, low-pressure air.
Is there refraction at the Zenith?
No. Light entering the atmosphere from directly overhead is not bent, so there is zero refraction at 90° altitude.