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How does a telescope work?
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Illustration comparing a reflecting telescope, which uses mirrors to focus light, and a refracting telescope, which uses lenses, both mounted on tripods and pointed at the night sky. Galileo's telescopes Side-by-side comparison of the Carina Nebula, with the James Webb Space Telescope image on the left showing sharp, detailed stars and gas clouds, and the Hubble image on the right with softer, more diffuse colors. Comparison between the Hubble and Webb space telescopes.
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Illustration comparing a reflecting telescope, which uses mirrors to focus light, and a refracting telescope, which uses lenses, both mounted on tripods and pointed at the night sky.
reflecting and refracting telescopes A reflecting telescope focuses light rays by reflecting them off a curved mirror. In the Newtonian type of reflector, left, a secondary mirror deflects the light rays through the eyepiece in the side of the tube. A refracting telescope, right, bends the light rays with a glass lens.

How does a telescope work?

Written by
Elijah Tan
Elijah Tan was an Editorial Intern at Encyclopædia Britannica. He is studying Astrophysics and Science Communication at the University of Chicago, where he writes for the Chicago Maroon.
Elijah Tan
Fact-checked by
Britannica Editors
Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....
Britannica Editors
Last updated
•History

Telescopes have upended astronomy again and again by illuminating what was previously invisible to the naked eye. Our eyes and our telescopes “see” in the same way, by collecting light rays and focusing them to a point. Our eyes collect light through our pupils, tiny openings only a few millimeters in diameter, and a lens inside our eyes focuses the light onto an optic nerve. The difference between our naked eyes and a telescope is...

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