The zero point of the absolute magnitude scale is actually defined as a fixed luminosity of 3.0128 × 10 W. Therefore, the absolute magnitude can be calculated from a luminosity in watts: M b o l = − − 2.5 log 10 ⁡ ⁡ L ∗ ∗ L 0 ≈ ≈ − − 2.5 log 10 ⁡ ⁡ L ∗ ∗ + 71.1974 where L 0 is the zero point luminosity 3.0128 × 10 W