Observing · Physics · The Sun
Refraction
Say it: rih-FRAK-shun IPA: /rɪˈfrækʃən/ noun
Refraction: The bending of light as it passes at a slant from one material into another, such as from space into Earth's air.
Light travels a little more slowly in denser air, so a ray from a star curves as it comes down through the atmosphere. Objects near the horizon therefore look a little higher than they really are.
- Example
- Refraction keeps the setting Sun in view for a short while after it has really dropped below the horizon.
- Why astronomers use it
- Sunrise and sunset times, and precise star positions, have to allow for it.
- Tiny cosmic connection
- Refraction lifts the bottom of a setting Sun more than the top, which is why the Sun can look squashed on the horizon.
Skywatcher Observing Physics The Sun
Where to check it
- US Naval Observatory: Rise, set and twilight definitions (opens in a new tab)
- Wikipedia: Atmospheric refraction (opens in a new tab)
Written for Cool Moon Facts in its own words; the sources cover the same idea in more depth.