OrbitLab

Absolute Magnitude Calculator

How bright is this object, really?

Apparent magnitude (m)

Distance (parsecs)

Absolute magnitude

What you entered

Apparent magnitude (m): 0Distance (parsecs): 10

1
5 × (log₁₀(d) − 1)
5 × (log₁₀(10) − 1)= 0
2
M = m − 5(log₁₀(d) − 1)
0 − 0= 0

Result

Absolute magnitude: 0

Corrected for distance, this object's true (absolute) magnitude is 0.

Absolute magnitude from apparent magnitude and distance

Absolute magnitude strips distance out, giving brightness as it would appear from exactly 10 parsecs. It is how you compare stars fairly.

Object	Apparent magnitude	Distance	Absolute magnitude
The Sun	-26.74	0.000004848 pc	4.832
Sirius	-1.46	2.64 pc	1.432
Alpha Centauri A	0.03	7.68 pc	0.603
A star at 10 pc	4.83	10 pc	4.830
Deneb-like supergiant	1.25	132 pc	-4.353

The Sun looks overwhelmingly the brightest object in our sky at -26.74, but at a standard 10 parsecs it would be a modest magnitude 4.8 star, barely visible. At 10 parsecs apparent and absolute magnitude are equal by definition.

Removing distance from the equation

Absolute magnitude answers 'how bright would this look from a standard 10 parsecs away?' — it's the fair, distance-corrected way to compare the true brightness of objects at wildly different distances.

Why this matters for comparing stars

Two stars can have identical apparent brightness in the sky purely by coincidence of distance — absolute magnitude is what actually reveals which one is the intrinsically more luminous star.

Frequently asked questions

A star appears at magnitude +3.0 and is 50 parsecs away — what is its absolute magnitude?

M = m - 5 × log10(d/10) = 3.0 - 5 × log10(50/10) = 3.0 - 5 × 0.699 = -0.5. Intrinsically quite bright — comparable to a red giant.

How is absolute magnitude different from the luminosity calculator?

Absolute magnitude is a logarithmic brightness scale. The luminosity calculator gives total power output in watts (or solar luminosities) from radius and temperature via Stefan-Boltzmann. They measure the same property in different units.

What is the absolute magnitude of the Sun?

+4.83. This makes our Sun an average main-sequence star. The brightest stars have absolute magnitudes around -8 to -10, and the faintest red dwarfs are around +16.

Can absolute magnitude be negative?

Yes — negative absolute magnitude means the star is intrinsically very luminous. Betelgeuse has M ≈ -5.6, meaning it would appear extremely bright even at the standard 10-parsec distance.