Luminosity distance

The dimensionless luminosity distance  D _L indicates how far away an astronomical object appears due to its apparent brightness  m , based on its otherwise known absolute brightness  M :

${\displaystyle D_{L}=10^{{\frac {m-M}{5\,\mathrm {mag} }}+1}}$

Since the absolute brightness is related to a distance of 10 parsecs , the luminosity distance implicitly has exactly this unit.

The difference between apparent and absolute brightness, also called the distance module, results from the luminosity distance by changing the above equation to:

${\displaystyle \Leftrightarrow m-M=5\,\mathrm {mag} \cdot (\log _{10}{D_{L}}-1)}$

In the case of more distant objects in particular, it can be complicated to calculate the luminosity distance based on the true distance, since the light can be absorbed in cosmic dust clouds ( interstellar extinction ). In addition, the underlying cosmological model also plays a role for very long distances . In the case of relatively close objects, however, it can be assumed that the luminosity distance roughly corresponds to the real distance.

See also

• Comparison of brightness