Hubble Space Telescope

The Hubble Space Telescope (HST) is a space-based astronomical observatory operated through a partnership between the United States National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA). Named for astronomer Edwin Hubble, it was developed as a long-lived observatory rather than a single-purpose probe. Its 2.4-metre reflecting telescope was deployed in low Earth orbit, about 600 kilometres above the planet.

Hubble's position above most of Earth's atmosphere is central to its work. The atmosphere blurs some astronomical images and blocks much ultraviolet light, while also adding background in parts of the infrared spectrum. Hubble's instruments observe ultraviolet, visible and near-infrared wavelengths, allowing astronomers to examine objects from the Solar System to very distant galaxies. Cameras record images, while spectrographs separate light by wavelength to reveal information about astronomical objects.

Hubble's modular design included handholds and grapple fixtures so astronauts could reach, repair and upgrade the observatory during space-shuttle visits. This feature proved crucial soon after launch, when engineers found that the primary mirror had a shape error called spherical aberration. The flaw caused early images to appear blurred, but it did not make the telescope unusable.

During the first servicing mission in December 1993, astronauts installed corrective optics and new instruments, bringing the incoming light into sharper focus. Four further servicing missions replaced or repaired equipment and added more capable instruments. On the final mission, in 2009, astronauts installed the Wide Field Camera 3 and Cosmic Origins Spectrograph and repaired two instruments that had stopped working. The upgrades extended the observatory's capabilities without returning it to Earth.

Hubble collects observations selected through a competitive process in which astronomers propose investigations for peer review. The Space Telescope Science Institute (STScI) coordinates the observatory's science operations, calibrates and distributes observation data, and maintains an archive. Researchers can use archived observations to pursue questions beyond the original purpose of a program.

Hubble's long-running observations have contributed to work on many subjects, including stars and planetary systems, galaxies, and the history and expansion of the universe. For example, ESA describes Hubble observations of discs of gas and dust around young stars and measurements of exoplanet atmospheres. Its ultraviolet access and detailed imaging complement other observatories, including the James Webb Space Telescope, which works in tandem with Hubble on astronomical research.