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SESK: Stuff Everyone Should Know · sesk.info/astro-spectra-differ-by-temperature

Why do the spectra of different stars look so different?

Mostly because of temperature, not because stars are made of different stuff.

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  1. They are made of different elements
  2. They move at different speeds
  3. They have different temperatures ✔

Why: Most stars have nearly the same makeup as the Sun. Temperature decides which atoms are ionized or excited enough to make lines. That is why hydrogen lines are weak in both the hottest and coolest stars.

Huh, didn't know that: In the hottest stars, hydrogen atoms are completely ionized, so they make almost no hydrogen lines.

The dad joke
Two stars compared spectra. One said, we're the same inside, you're just running a temperature.
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References

Answer: They have different temperatures. Most stars have nearly the same makeup as the Sun. Temperature decides which atoms are ionized or excited enough to make lines. That is why hydrogen lines are weak in both the hottest and coolest stars.

  1. Astronomy 2e, 17.3 The Spectra of Stars (and Brown Dwarfs) openstax.org/books/astronomy-2e/pages/17-3-the-spectra-of-stars-and-brown-dwarfs
    The primary reason that stellar spectra look different is because the stars have different temperatures .
    Checked 2026-10-10.

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