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
Galaxy Candela
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