Absolute Magnitude Calculator
Enter an object's apparent magnitude and distance in parsecs to compute its absolute magnitude using the distance modulus M = m − 5 log₁₀(d) + 5.
Input Parameters
As observed from Earth. Lower = brighter; negative values are allowed.
1 pc = 3.086 × 10¹³ km ≈ 3.26 light-years.
Known stars
Distance Modulus Formula
M = m − 5 log₁₀(d) + 5
d in parsecs | Reference distance: 10 pc
Results
Enter apparent magnitude and distance to compute absolute magnitude.
Absolute Magnitude (M)
—
Brightness at 10 pc reference distance
Distance Modulus (m − M)
—
Positive = object is farther than 10 pc
Luminosity vs. Sun (L/L☉)
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Based on M☉ = 4.83 (visual band)
Rough Luminosity Class
—
—
Absolute Magnitude Scale Reference
| Object | M (abs. mag.) | L/L☉ |
|---|---|---|
| Eta Carinae (hypergiant) | −12 | ~5,000,000 |
| Rigel (blue supergiant) | −7.8 | ~120,000 |
| Sirius A (A-type main-sequence) | +1.4 | ~25 |
| Sun (G-type main-sequence) | +4.83 | 1 |
| Proxima Centauri (red dwarf) | +15.5 | ~0.0017 |
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Summary
Enter an object's apparent magnitude and distance in parsecs to compute its absolute magnitude using the distance modulus M = m − 5 log₁₀(d) + 5.
How it works
- Enter the apparent magnitude (m) of the object — this is the brightness as seen from Earth. Brighter objects have lower or negative values.
- Enter the distance to the object in parsecs (pc). One parsec equals 3.086 × 10¹³ km or about 3.26 light-years.
- The calculator applies the distance modulus: M = m − 5 × log₁₀(d) + 5.
- The result is the absolute magnitude — the brightness the object would appear at exactly 10 parsecs.
- A luminosity ratio relative to the Sun is also shown, computed from the difference between the object's absolute magnitude and the Sun's (M☉ = 4.83).
Use cases
- Compare the true luminosity of stars regardless of their distance from Earth.
- Convert observational apparent magnitudes to intrinsic brightness for stellar catalogs.
- Solve distance modulus problems in astronomy coursework.
- Check calculated absolute magnitudes against published values for known stars.
- Estimate how bright a star would appear if it were moved to 10 pc.
- Derive luminosity ratios between stars and the Sun for HR diagram placement.
Frequently Asked Questions
Last updated: 2026-07-21 ·
Reviewed by Nham Vu