Astronomy & space · University
Magnitude difference from a flux ratio
The fluxes must refer to the same measurement band and calibration convention.
Method and conditions
The fluxes must refer to the same measurement band and calibration convention.
m₂ − m₁ = −2.5 log₁₀(F₂/F₁)
Worked examples
Source 2 has 52 times the flux of source 1 in the same band. Find m₂−m₁. Round the final result to 4 decimal places if needed.
Use −2.5 log₁₀(52); the brighter source has the smaller magnitude.
-4.29
Source 2 has 103 times the flux of source 1 in the same band. Find m₂−m₁. Round the final result to 4 decimal places if needed.
Use −2.5 log₁₀(103); the brighter source has the smaller magnitude.
-5.0321
Try it
Source 2 has 110 times the flux of source 1 in the same band. Find m₂−m₁. Round the final result to 4 decimal places if needed.
Source 2 has 139 times the flux of source 1 in the same band. Find m₂−m₁. Round the final result to 4 decimal places if needed.
Check your work
Answers and marking notes
- -5.1035
Use −2.5 log₁₀(110); the brighter source has the smaller magnitude.
- -5.3575
Use −2.5 log₁₀(139); the brighter source has the smaller magnitude.
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