# Extinction

Also called: airmass, atmospheric extinction.

The dimming of starlight by the atmosphere, which grows quickly towards the horizon.

Light from overhead passes through one “airmass” of atmosphere; at 30° altitude it passes through two, and near the horizon through ten or more. Each airmass dims stars by roughly 0.2–0.3 [magnitudes](https://astropilot.space/glossary/magnitude) on a clear night, more in hazy air — so a faint galaxy low in the sky can lose a whole magnitude or more.

**In AstroPilot:** AstroPilot's ratings include extinction for each object's altitude and the forecast haze.

**Related:** [Altitude](https://astropilot.space/glossary/altitude.md), [Transparency](https://astropilot.space/glossary/transparency.md), [Aerosols](https://astropilot.space/glossary/aerosols.md)

From the AstroPilot astronomy glossary: https://astropilot.space/glossary/extinction