### distance modulus

**(μ)**
(apparent magnitude minus absolute magnitude)

A star or other astronomical body's **distance modulus** (**μ**)
is an indication of its distance consisting of
the difference between
its apparent magnitude and its absolute magnitude.
It is directly related to the distance to the star
if there is no absorption.

μ = 5 log_{10}d - 5

- μ -
*distance modulus*.
- d - distance in parsecs.

An object's **luminosity distance** (**D**_{L})
is the distance implied by the distance modulus,
i.e., a distance to the object implied by the
object's actual absolute magnitude and its apparent magnitude.
The term *luminosity distance* is basically just the actual
distance for distances to Milky Way stars if reddening
is not a big issue, but for objects at cosmological distances
(high redshift), curvature can make the actual
distance diverge from that implied by the above relation.
Straight-forward determination of this *luminosity distance*
using the above equation is possible if the actual absolute magnitude
is known by some other means, such as if it is a standard candle.

(*measure,EMR,logarithmic,distance,magnitude*)
**Further reading:**

http://en.wikipedia.org/wiki/Distance_modulus

http://en.wikipedia.org/wiki/Luminosity_distance

**Referenced by pages:**

planetary nebula luminosity function (PNLF)

pulsar timing array (PTA)

redshift-magnitude relation

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