A small number. A bright star.

Stellar brightness

Compare two stars on the magnitude scale: 5 magnitudes is exactly 100× in brightness and 1 magnitude about 2.512×. Enter magnitudes to get the flux ratio.

Classroom activity Teaching with this lab?

Stellar brightnessInteractive model

Flux A / Flux B100×

Magnitude difference5 mag

Brighter objectObject A

Your experiment

Object A magnitude mag

Object B magnitude mag

10^(0.4 × (6 − 1)) = 100. Object A delivers 100 times the flux of object B in the same band.

How it works

Brightness A / Brightness B = 10^(0.4 × (mB − mA))

The magnitude scale runs backward: smaller numbers mean brighter objects. It is logarithmic, so a difference of five magnitudes corresponds to a factor of one hundred in brightness.

The Magnitude Scale Explained: Star Brightness ↗

About this model
Both magnitudes must refer to the same photometric band. This compares received flux, not intrinsic luminosity. Symbol sizes use a compressed scale.

Key formulas

Quantity	Formula	Note or example
Brightness ratio	F_A / F_B = 10^(0.4 × (m_B − m_A))	Same photometric band
Magnitude difference	m_B − m_A = 2.5 log₁₀(F_A / F_B)
One magnitude	≈ 2.512× in brightness	The fifth root of 100

Worked examples

Each row uses one of this lab’s presets and the same model as the interactive tool.

Example	Flux A / Flux B	Magnitude difference	Brighter object
Five magnitudes	100×	5 mag	Object A
Equal brightness	1×	0 mag	Equal
One magnitude	2.51×	1 mag	Object A

Keep wondering