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SESK: Stuff Everyone Should Know · sesk.info/astro-wiens-law

As a star gets hotter, its peak emission moves which way?

To shorter wavelengths (Wien's law), so hot stars look bluer.

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  1. To longer wavelengths
  2. To shorter wavelengths ✔
  3. It stays the same

Why: Hotter matter radiates more at every wavelength, and its peak shifts toward the blue. That is why a stove burner goes from dull red to orange as it heats, and blue stars are hotter than red ones.

Huh, didn't know that: Color gives astronomers a rough thermometer for stars.

The dad joke
Blue stars are so hot, they're cool.
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References

Answer: To shorter wavelengths. Hotter matter radiates more at every wavelength, and its peak shifts toward the blue. That is why a stove burner goes from dull red to orange as it heats, and blue stars are hotter than red ones.

  1. OpenStax Astronomy 2e, 5.2 The Electromagnetic Spectrum openstax.org/books/astronomy-2e/pages/5-2-the-electromagnetic-spectrum
    The higher the temperature, the shorter the wavelength at which the peak amount of energy is radiated (this is known as Wien’s law).
    Checked 2026-10-10.

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