Height of the atmosphere from twilight
Altura de la atmósfera por el crepúsculo
- Date
- c. 1070 · confidence low
- Place
- Jaén, Andalusia, Spain
- Credited to
- Ibn Mu'adh al-Jayyani (attributed)
- People
- 👤 Ibn Mu'adh al-Jayyani989–1050
- Field
- Cosmos & Earth
⚠️ Disputed: the sources disagree.
What was discovered
The treatise on twilight calculates that dawn begins when the Sun is 18° below the horizon and deduces that the layer of air reflecting the light is about 52 miles (some 84 km) high. It is the first geometric estimate of the height of the atmosphere.
In Latin (Liber de crepusculis) it was attributed to Alhazen; A. I. Sabra and others attribute it to Ibn Mu'adh of Jaén, who is also credited with a treatise on spherical trigonometry.
What it led to
- studies of atmospheric refraction
- definition of astronomical twilight (18°)
- Kepler's atmospheric optics