Surface brightness
The surface brightness is luminance. It is used in astronomy to detect the brightness of astronomical objects with a large surface area, such as galaxies or the night sky.
Calculation
The surface brightness is the ratio of apparent magnitude H and area A:
Or log in magnitudes:
If one replaces the apparent brightness of the object H, it follows by the apparent magnitude m in magnitudes:
Units
The surface brightness is measured in cd / m². In astronomy, the unit mag / arcsec ² in use; the unit S10 describes the brightness of the number of stars the brightness 10 mag within a square degree.
Conversions:
- If B in cd / m² and X like in / arcsec ², then: B = 1.084 x 105 x 10 ( -0.4 · X)
- 1 S10 = 0.69 · 10-6 cd / m²
Example: Weakest brightness of the night sky under optimal conditions: 21.6 mag / arcsec ² = 2.5 × 10-4 cd / m² = 370 S10
References
- Astrophysics
- Astronomical measure