What Is Apparent Magnitude?
Why is a magnitude-1 star brighter than magnitude 5? And why does smaller mean brighter?
Apparent magnitude measures how bright a star looks from Earth: the smaller the number, the brighter the star. Magnitude 1 is brilliant, magnitude 6 is about the naked-eye limit, and none of it depends on the star’s actual distance.
A ruler that runs backwards
- Magnitude 1
- very bright — e.g. Regulus at 1.36
- Magnitude 3
- bright, visible from the city
- Magnitude 5
- fainter — needs a decent dark sky
- Magnitude 6
- naked-eye limit under dark skies
Magnitudes trace back to the ancient Greek ranking (brightest = 1st, faintest = 6th) and were later made mathematical: one magnitude step equals about 2.5× in brightness. The scale now extends negative — Sirius, the brightest star in the night sky, is about magnitude −1.5.
What it does not tell you
Apparent magnitude is not intrinsic brightness. A far, blazing star can look identical to a close, dim one. Once you own a star, its magnitude tells you how easy it will be to spot: the lower the number, the brighter the star — roughly magnitude 3 and brighter is visible from a city. Your certificate and star page carry its true value.