Magnitude Converter
Astronomers measure brightness on a backwards, logarithmic scale where smaller numbers are brighter. Convert between how bright a star looks, how bright it really is, and how far away it is.
Magnitude converter
Apparent and absolute magnitude, distance, and how much brighter one star is than another.
How bright it looks from Earth.
Dimming by dust on the way. Leave at 0 if unknown.
Lower numbers are brighter. The brightest objects have negative magnitudes, so Sirius at −1.46 outshines Vega at 0.03.
Brightness ratio
Compare any two magnitudes, apparent or absolute.
Absolute magnitude
M = 1.43
How bright it would look from a standard distance of 10 parsecs (32.6 light years).
- Apparent magnitude (m)
- −1.46
- Absolute magnitude (M)
- 1.43
- Distance in parsecs
- 2.64
- Distance in light years
- 8.6105
- Distance modulus (m − M)
- −2.89
- Visual luminosity
- 22.87 × Sun
Brightness ratio
3.945x
The first object is 3.945 times brighter (a difference of 1.49 magnitudes).
Uses m − M = 5 log₁₀(d) − 5 + A with d in parsecs. Real stars vary, and published distances carry uncertainties.
How this is calculated
- 1
The distance modulus
m − M = 5 log₁₀(d) − 5 + A, where m is apparent magnitude, M is absolute magnitude, d is the distance in parsecs and A is the dimming by interstellar dust.
- 2
Solve for what is missing
M = m − 5 log₁₀(d) + 5 − A gives the true brightness, m = M + 5 log₁₀(d) − 5 + A gives the brightness seen from Earth, and d = 10^((m − M + 5 − A) ÷ 5) gives the distance.
- 3
Brightness ratio
Each step of one magnitude is a factor of 10^0.4, about 2.512. Five magnitudes is exactly 100 times, so ratio = 10^(0.4 × Δm).
- 4
Parsecs and light years
One parsec is 3.26156 light years. Absolute magnitude is defined as the brightness at 10 parsecs, or 32.6 light years.
Frequently asked questions
What is the difference between apparent and absolute magnitude?
Apparent magnitude is how bright an object looks from Earth. Absolute magnitude is how bright it would look from a standard distance of 10 parsecs, which lets you compare the real output of stars at different distances.
Why are brighter stars given lower magnitudes?
The scale comes from ancient Greek astronomers, who called the brightest stars first magnitude and the faintest sixth. Modern astronomers kept the order and extended it past zero, so the very brightest objects have negative values.
How much brighter is a magnitude 1 star than a magnitude 6 star?
Exactly 100 times. A difference of 5 magnitudes was fixed as a factor of 100 by Norman Pogson in 1856, so each single magnitude is the fifth root of 100, about 2.512.
What is the absolute magnitude of the Sun?
About 4.83 in visible light. Seen from 10 parsecs the Sun would be an ordinary star of magnitude 4.8, easy to see from a dark site but lost in city lights.