SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/astro-star-color-temperature

What does a star's color mainly tell you?

Its surface temperature: blue-white stars are hot, red stars are cool.

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  1. Its surface temperature ✔
  2. Its distance from Earth
  3. Its age only

Why: By Wien's law, hotter objects peak at shorter wavelengths. So blue-white stars like Spica (about 25,000 K) are far hotter than the yellow Sun (about 6000 K) or red Betelgeuse (about 3000 K).

Huh, didn't know that: Red stars give off much of their energy in the infrared, and blue stars in the ultraviolet.

The dad joke
Why did the red star feel left out? Everyone else was so cool to be blue.
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References

Answer: Its surface temperature. By Wien's law, hotter objects peak at shorter wavelengths. So blue-white stars like Spica (about 25,000 K) are far hotter than the yellow Sun (about 6000 K) or red Betelgeuse (about 3000 K).

  1. Astronomy 2e, 17.2 Colors of Stars openstax.org/books/astronomy-2e/pages/17-2-colors-of-stars
    Blue-white stars are much hotter than the Sun, whereas red stars are cooler.
    Checked 2026-10-10.

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