Logarithmic astronomical magnitudes
A magnitude difference encodes a flux ratio on a logarithmic scale: brighter objects have smaller magnitudes.
Key knowledge
A magnitude difference encodes a flux ratio on a logarithmic scale: brighter objects have smaller magnitudes. Absolute magnitude refers to the same band and magnitude system at a distance of 10 parsecs without extinction. Comparing different bands or zero-point systems requires their specified calibration.
Values and equations
m₁ − m₂ = −2.5 log₁₀(F₁/F₂)
- m₁,m₂
- apparent magnitudes in one system mag
- F₁,F₂
- fluxes in the same band same flux units
m − M = 5 log₁₀(d / 10 pc)
- m
- apparent magnitude mag
- M
- absolute magnitude mag
- d
- distance pc
Conditions and scope
- Fluxes in the difference equation use the same band response and zero point.
- The elementary distance modulus neglects extinction and cosmological spectral corrections.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read five magnitudes per factor of 100 in the textbook and band/zero-point/distance-modulus definitions in MIT notes; corrected the MIT notes' reversed sign in the relative-magnitude equation.
2026-10-10 · Independent AI editorial review: All26 Life-authored Cosmos compact statements, conditions, displayed equations and all56 origin semantic links read. Entire26-entry author statement/source matrix and explicit exclusions assessed. Targeted independent primary sections are listed below; this does not claim every referenced source body or proof was independently re-read. This is scoped AI reference-content review, not human disciplinary certification or whole-field completion. Receipt: cosmos-life-independent-content-review.1.
Entry details
Permanent link to this entry ↗- Record identity
- uni-cosmos-magnitude
- Revision
- core.1
- Structured reference record
- University core expansion