Apparent Magnitude

Apparent magnitude is the standard astronomical measure of how bright an object appears in the sky, as opposed to how luminous it actually is. The scale is logarithmic and inverted: each step of one magnitude is about 2.5× brighter, and smaller or negative numbers mean a brighter object. Sirius, the brightest star, is −1.5; Venus reaches about −4.5; the full Moon is −12.7. For satellites, apparent magnitude depends on size, surface reflectivity, altitude and the Sun-observer viewing geometry. The ISS can flare to magnitude −4, rivalling Venus, while most Starlink satellites sit between +2 and +6 — at or below the naked-eye limit of roughly +6.