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SESK: Stuff Everyone Should Know · sesk.info/astro-light-gathering-area

A 4-meter telescope mirror collects how much more light than a 1-meter mirror?

16 times as much, because area grows with diameter squared.

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  1. 4 times
  2. 8 times
  3. 16 times ✔

Why: Light gathering depends on the mirror's area, and area grows with the square of the diameter. Four times wider means 4 x 4 = 16 times the collecting area.

Huh, didn't know that: Astronomers compare telescopes by aperture, the diameter of the main lens or mirror.

The dad joke
Why did the telescope bring a bucket? It wanted to catch more starlight.
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References

Answer: 16 times. Light gathering depends on the mirror's area, and area grows with the square of the diameter. Four times wider means 4 x 4 = 16 times the collecting area.

  1. OpenStax Astronomy 2e, 6.1 Telescopes openstax.org/books/astronomy-2e/pages/6-1-telescopes
    can collect 16 times as much light as a telescope that is 1 meter in diameter.
    Checked 2026-10-10.

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