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SESK: Stuff Everyone Should Know · sesk.info/astro-keck-segmented-mirror

How does each 10-meter Keck telescope make its giant mirror?

36 hexagonal segments working together as one mirror.

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  1. One solid 10-meter glass disk
  2. 36 hexagonal segments kept aligned by motors ✔
  3. A spinning pool of liquid mercury

Why: Each Keck mirror is 36 hexagons, each 1.8 meters wide. Computer-driven actuators keep adjusting them so they act like one perfectly shaped mirror. Webb later used the same segmented idea.

Huh, didn't know that: The twin Keck telescopes sit on Maunakea in Hawaii, about 4,200 meters up.

The dad joke
Keck has 36 mirrors and still never has a bad hair day.
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References

Answer: 36 hexagonal segments kept aligned by motors. Each Keck mirror is 36 hexagons, each 1.8 meters wide. Computer-driven actuators keep adjusting them so they act like one perfectly shaped mirror. Webb later used the same segmented idea.

  1. OpenStax Astronomy 2e, 6.2 Telescopes Today openstax.org/books/astronomy-2e/pages/6-2-telescopes-today
    combining the light from 36 separate hexagonal mirrors, each 1.8 meters wide
    Checked 2026-10-10.

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