modulus of distance

(′mäj·ə·ləs əv ′dis·təns)

(astronomy) The quantity m-M, where M is the absolute magnitude of a given star and m is its apparent magnitude. Also known as distance modulus.

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astronomy A simple expression for the distance from Earth of an astronomical object, being the difference between its observed apparent magnitude and its computed absolute magnitude (see stellar magnitude). If m and M are those respective magnitudes, then the modulus is (m - M) and the distance d in parsecs is given by

log₁₀ (d) = ((m - M) + 5)/5

Used by professional astronomers for distant star clusters and galaxies.