What does OBAFGKM stand for?

The mnemonic "Oh Be A Fine Guy/Girl, Kiss Me" helps remember the order from hottest to coolest.

What are the subclasses (0-9)?

Each letter class is divided into 10 subclasses (0 = hotter, 9 = cooler). The Sun is G2, meaning near the hot end of the G class.

What about L, T, and Y classes?

These extend the sequence below M for brown dwarfs: L (1300-2000 K), T (500-1300 K), Y (< 500 K).

Free Spectral Class Estimator

Estimate which spectral class (O, B, A, F, G, K, M) a star belongs to based on its effective temperature.

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Effective Temperature

Spectral Class Code

Peak Wavelength501.5 nm

Spectral Class Code vs Effective Temperature

View formula & how it works →

Spectral Classification (OBAFGKM)

Stars are classified by surface temperature into spectral types:

ClassTemperature RangeColour O> 30 000 KBlue B10 000 - 30 000 KBlue-white A7 500 - 10 000 KWhite F6 000 - 7 500 KYellow-white G5 200 - 6 000 KYellow K3 700 - 5 200 KOrange M< 3 700 KRed

The output code: 7=O, 6=B, 5=A, 4=F, 3=G, 2=K, 1=M.

Example Calculation

The Sun at 5778 K.

015778 K falls between 5200 and 6000 K.
02Spectral class: G (code 3)
03Peak wavelength: 2897800 / 5778 = 501.5 nm (green)
04The Sun is a G2V star.

Frequently Asked Questions

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