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A difference of 5 magnitudes means what brightness ratio?

Exactly 100 times.

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  1. Exactly 100 times ✔
  2. Exactly 5 times
  3. Exactly 10 times

Why: Astronomers defined 5 magnitudes as a factor of 100. Each single magnitude is the fifth root of 100, about 2.5 times. So a magnitude 1 star is 100 times brighter than a magnitude 6 star.

Huh, didn't know that: The scale was put on this precise footing in the nineteenth century.

The dad joke
Magnitudes are like golf scores: lower is better.
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References

Answer: Exactly 100 times. Astronomers defined 5 magnitudes as a factor of 100. Each single magnitude is the fifth root of 100, about 2.5 times. So a magnitude 1 star is 100 times brighter than a magnitude 6 star.

  1. OpenStax Astronomy 2e, 17.1 The Brightness of Stars openstax.org/books/astronomy-2e/pages/17-1-the-brightness-of-stars
    a difference of five magnitudes corresponds exactly to a brightness ratio of 100:1.
    Checked 2026-10-10.

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