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How can a Telescope Image Both a Galaxy and the Stars within it?

-- | January 1, 2014

Question: How can Hubble give pictures with different zoom levels? If telescopes are constructed with a fixed focal length and cannot “zoom”. How come that Hubble can see individual stars in the Andromeda Galaxy http://www.spacetelescope.org/images/heic1112a/. But can also see the whole galaxy http://www.spacetelescope.org/images/opo0315f/. — Nikola

Answer: Many telescopes, the Hubble Space Telescope being one of them, uses array detectors to capture the light from stars and galaxies. Array detectors are composed of individual pixels which determine the telescope’s ability to separate objects that are very close to each other or to detect objects that are very small. By putting many of these pixels together as an array, we can stitch together many pixels to make a picture, or “image” of larger objects while still retaining the ability to see small objects. This is how we are able to see both galaxies and the individual stars within those galaxies.

Jeff Mangum

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