How this calculation works
A source looks fainter as its light spreads over a larger area, and intervening material can dim it further. The distance modulus relates apparent brightness to a known absolute magnitude while keeping extinction as a separate correction. This page estimates classical photometric distance from those three entered magnitudes. It does not infer a star’s intrinsic brightness from its color or identify a standard candle automatically.
m − M − A = 5 log10(dpc) − 5; dpc = 10^[(m−M−A+5)/5]A worked example
An apparent magnitude of ten and absolute magnitude of five with zero extinction give corrected modulus five. Distance is one hundred parsecs, or about 326.156 light years. The corresponding inverse-distance parallax is ten milliarcseconds. If one magnitude of extinction is assigned in the same band, distance falls to about 63.0957 parsecs rather than remaining one hundred.
Good to know
This is a Euclidean distance-modulus relation. Cosmological luminosity distance, redshift corrections, unresolved companions and population-based luminosity calibration are absent. Uncertainty in absolute magnitude or extinction can dominate the inferred distance. The page does not produce a posterior distance distribution or claim that the entered magnitudes are measured accurately.
Reference: Western Kentucky University — magnitudes distance and extinction (opens in a new tab) ↗
What this calculation answers
A source looks fainter as its light spreads over a larger area, and intervening material can dim it further. The distance modulus relates apparent brightness to a known absolute magnitude while keeping extinction as a separate correction.
This page estimates classical photometric distance from those three entered magnitudes. It does not infer a star’s intrinsic brightness from its color or identify a standard candle automatically.
The Elliptic orbit apsides speed and period calculator explains the logarithmic operation in the magnitude relation; magnitude differences become multiplicative distance ratios rather than additive parsecs.
Use the right input conventions
Apparent magnitude, absolute magnitude and extinction must all refer to the same passband. Absolute magnitude is defined at ten parsecs without extinction. Mixing a visual-band magnitude with an infrared extinction value invalidates the comparison.
Extinction is entered as a nonnegative dimming amount. It is subtracted from observed apparent-minus-absolute magnitude before deriving distance. The equivalent inverse-distance parallax is a conversion of the derived distance, not an independent measured parallax.
Interpret the result
A five-magnitude increase in corrected distance modulus multiplies distance by ten. The magnitude scale is logarithmic, so adding one magnitude does not add a fixed number of parsecs.
At fixed observed and absolute magnitude, a larger extinction assumption implies a smaller inferred distance. Some of the observed faintness is then attributed to obscuration rather than geometric spreading.
Work through the example
An apparent magnitude of ten and absolute magnitude of five with zero extinction give corrected modulus five. Distance is one hundred parsecs, or about 326.156 light years.
The corresponding inverse-distance parallax is ten milliarcseconds. If one magnitude of extinction is assigned in the same band, distance falls to about 63.0957 parsecs rather than remaining one hundred.
Where the model stops
This is a Euclidean distance-modulus relation. Cosmological luminosity distance, redshift corrections, unresolved companions and population-based luminosity calibration are absent.
Uncertainty in absolute magnitude or extinction can dominate the inferred distance. The page does not produce a posterior distance distribution or claim that the entered magnitudes are measured accurately.
A few questions, answered
Why does more extinction reduce the inferred distance?
For the same observed faintness, more assumed obscuration leaves less dimming to explain by distance.
What changes in the comparison?
Assign one magnitude of same-band extinction and inspect the shorter photometric distance.