Star Color and Temperature Calculator

Stars emit light as approximate blackbodies, meaning their color is determined by their surface temperature.

Wien’s Displacement Law gives the wavelength of peak emission:

λ_max = 2,897,771 / T nanometers

Where T is temperature in Kelvin.

Color interpretation:

• λ_max < 400 nm → ultraviolet (star appears blue-white)
• 400–450 nm → violet/blue
• 450–500 nm → blue
• 500–570 nm → green (but stars never look green due to broad spectrum: appear white)
• 570–590 nm → yellow
• 590–620 nm → orange
• 620–700 nm → red

• 700 nm → infrared (star appears deep red or brown dwarf)

B-V color index to temperature: The B-V index measures the difference in brightness in blue (440 nm) vs visual (550 nm) filters. A hot blue star has negative B-V; a cool red star has a large positive B-V.

T ≈ 4600 × (1/(0.92 × B-V + 1.7) + 1/(0.92 × B-V + 0.62))

Spectral class temperature ranges:

• O: > 30,000 K (blue)
• B: 10,000–30,000 K (blue-white)
• A: 7,500–10,000 K (white), Sirius, Vega
• F: 6,000–7,500 K (yellow-white), Procyon
• G: 5,200–6,000 K (yellow), Sun, Alpha Centauri A
• K: 3,700–5,200 K (orange), Arcturus, Aldebaran
• M: < 3,700 K (red), Betelgeuse, Proxima Centauri

The human eye does not see most of the photons from stars — we see the integrated color across the spectrum. This is why even very hot stars appear white rather than violet or ultraviolet to our eyes.