Telescopes

Why Did We Put Glasses on the Hubble Telescope?

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If you can't make out the words on street signs, you correct your vision by wearing glasses. If NASA sends up a multi-billion-dollar telescope that can't make out the stars in galaxies, well—it corrects its vision with glasses, too. In essence, anyway. That's what happened with the Hubble Space Telescope: it wore "glasses" for more than 15 years.

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The core of spiral galaxy M100, imaged with Hubble before and after corrective optics.

If Telescopes Could Squint

NASA's Hubble Space Telescope launched on April 24, 1990 to great fanfare as the first astronomical observatory to be placed into orbit. But it didn't take long for scientists to realize something was wrong: the images it sent back were fuzzy. It turned out that the telescope's primary mirror had a flaw known as spherical aberration, which scattered some of the light that reached it. The cause was a tiny manufacturing error: the mirror was ground too flat by a depth of 4 microns, or roughly one fiftieth the width of a human hair.

An Ingenious Solution

To fix this, NASA rigged up a series of new mirrors to be placed in front of the original instruments. These were designed to catch the scattering light and help it focus on a single point in the same way corrective lenses help our eyes. The Corrective Optics Space Telescope Axial Replacement, or COSTAR, was installed in 1993 and worked like a charm, helping the Hubble bring such monumental images as The Pillars of Creation into sharp relief. As more instruments were installed with built-in corrections for the aberration, COSTAR gradually became obsolete. It was finally retired in 2009.

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Watch And Learn: Our Favorite Content About The Hubble Space Telescope

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Key Facts In This Video

  1. Hubble was launched with an irregularly shaped mirror that kept it from being able to focus properly. 00:43

  2. In 1993, NASA equipped Hubble with what amounts to eyeglasses, correcting its "vision" and allowing it to capture crystal clear images of the universe. 01:08

  3. Over the years, the Hubble Telescope has sent back many images, including highlights such as The Pillars of Creation, Comet Shoemaker-Levy 9, and the Deep Field image. 01:28

The Man the Hubble Space Telescope was Named After

Hubble Space Telescope - Extreme Deep Field

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