II. Reading. The Hubble Space Telescope (HST) is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation

The Hubble Space Telescope (HST) is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation.
A 2.4-meter (7.9 ft) aperture telescope in low Earth orbit, Hubble’s four main instruments observe in the near ultraviolet, visible, and near infrared spectra. The Large Space Telescope was renamed the Hubble Space Telescope (HST) in honour of Edwin Hubble, an American astronomer who, among other things, determined that the universe extended beyond the borders of Milky Way.

Hubble’s orbit outside the distortion of Earth’s atmosphere allows it to take extremely high-resolution images with almost no background light. Hubble’s Deep Field has recorded some of the most detailed visible-light images ever, allowing a deep view into space and time. Many Hubble observations have led to breakthroughs in astrophysics, such as accurately determining the rate of expansion of the universe.

Although not the first space telescope, Hubble is one of the largest and most versatile, and is well known as both a vital research tool and a public relations boon for astronomy. The HST was built by the United States space agency NASA, with contributions from the European Space Agency, and is operated by the Space Telescope Science Institute. The HST is one of NASA’s Great Observatories, along with the Compton Gamma Ray Observatory, the Chandra X-ray Observatory, and the Spitzer Space
Telescope.

Space telescopes were proposed as early as 1923. Hubble was funded in the 1970s, with a proposed launch in 1983, but the project was beset by technical delays, budget problems, and the Challenger disaster. When
finally launched in 1990, Hubble’s main mirror was found to have been ground incorrectly, compromising the telescope's capabilities. The optics were corrected to their intended quality by a servicing mission in 1993.

The Hubble Space Telescope’s elevated perspective and advanced optics allow it to peer farther away than previous ground-based optics are able to see. Because light takes time to travel long distances, the range of the HST makes it function similar to a time machine; the light it views from remote objects only reveals how that object appeared when the light left it, not how it appears today. Thus when we look at the Andromeda galaxy, 2.5 million light-years from Earth, we see it as it was 2.5 million years ago.

When astronomers pointed the HST to a seemingly-empty patch of sky, for instance, they captured an image of over 3,000 galaxies too distant to be detected by other telescopes. Some of the galaxies were so young, they had not yet begun serious star formation. Other deep field observations have since been taken, providing a wealth of information.

In addition to gazing at the early universe, Hubble also helped astronomers gauge how much time had passed since the Big Bang. By measuring a special kind of pulsing star known as a Cepheid variable, they were able to narrow down the age of the universe from its pre-HST range of
10 to 20 billion years to a more precise 13.7 billion years.

In addition to galaxies, the Hubble Space Telescope also examines individual stars in various stages of their evolution – from the clouds of dust that form infant stars to the corpses of those long since detonated, and those in between. It has even been able to peer outside of our galaxy, the Milky Way, and into its neighbours, the Magellanic Clouds and Andromeda Galaxy.

The Hubble Space Telescope may spend much of its time peering light-years from Earth, but on occasion it takes the time to photograph the planets travelling around our sun. High resolution images taken of Jupiter, Saturn, and even Pluto can provide insights that can only be topped by planetary probes circling the planets. Images from the HST allow scientists on Earth to monitor changes in the planet’s atmosphere and surface. When the comet Shoemaker-Levy crashed into the Jupiter in 1994, the Hubble Space Telescope photographed the fatal collision. The aftermath revealed
a great deal about the gas giant's atmosphere.

In orbit for more than two decades, the Hubble Space Telescope has provided scientists with a greater understanding of the planets, galaxy, and the whole universe.

Hubble is the only telescope designed to be serviced in space by astronauts. Between 1993 and 2002, four Space Shuttle missions repaired,
upgraded, and replaced systems on the telescope; a fifth mission was canceled on safety grounds following the Columbia disaster. However, after spirited public discussion, NASA administrator Mike Griffin approved one final servicing mission, completed in 2009. The telescope is now expected to function until at least 2014, and possibly 2020. Its scientific successor, the James Webb Space Telescope (JWST), is currently scheduled to be launched in 2018.