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Hubble Space Telescope

Above The Turbulent Atmosphere

The twinkling of stars is a barrier between astronomers and the information they wish to gather. In reality, stars do not twinkle but burn steadily; they only appear to ground observers to twinkle because atmospheric turbulence distorts their light waves en route to us. Although telescopes on Earth's surface incorporate enormous mirrors to gather starlight and sophisticated instruments to minimize atmospheric distortion, the images gathered still suffer from some image degradation. Recently much progress has been made in the use of adaptive optical systems. These systems aim lasers along a telescope's line of sight to measure atmospheric turbulence. This information is fed to computers, which calculate and apply an ever-changing counter-warp to the surface of the telescope's mirror (or mirrors) to undo the effect of the turbulence in real time. Adaptive optics are starting to overcome some of the problems caused by atmospheric turbulence. However, the fact that the Earth's atmosphere absorbs much of the electromagnetic spectrum cannot be overcome from the ground; only space-based telescopes can make observations at certain wavelengths (e.g., the infrared).

Scientists first conceived of an orbital telescope in the 1940s. The observatory proposed at that time was called, optimistically, the Large Space Telescope. By the 1970s, the concept had coalesced into an actual design, less "large" thanks to political backlash against the huge space-exploration budgets of the 1960s. In 1990, after a decade of development and years of delay caused by the Challenger shuttle disaster of 1986, the space shuttle Discovery deployed the Hubble Space Telescope into an orbit approximately 380 mi (612 km) above Earth. The way we see the universe was about to be changed—but not for another three years, due to a design flaw in the main mirror.

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Science EncyclopediaScience & Philosophy: Heterodyne to Hydrazoic acidHubble Space Telescope - Above The Turbulent Atmosphere, The Design, Hubble's Blurry Vision, Endeavor To The Rescue