The distance of a star as inferred from its position on the lower main sequence, where colour and absolute magnitude are tightly correlated by the colour–magnitude relation. If the colour is known, the absolute magnitude may be inferred. The difference between the apparent magnitude, m, and the absolute magnitude, M, is related to the parallax, π, in seconds of arc by the formula
log π = 0.2(M − m − 5).
Subjects: Astronomy and Astrophysics.