Hubble
Highlights from the Hubble Space Telescope.
Overview
Hubble has operated since 1990 and produced much of the imagery that defines public perception of astronomy. Its scientific importance rests less on the pictures than on what a stable, serviceable, above-the-atmosphere platform made measurable.
- Hubble launched in 1990 with a flawed primary mirror, corrected by a servicing mission in 1993.
- Five shuttle servicing missions replaced instruments and kept it scientifically current for decades.
- Its deep field observations showed that faint patches of apparently empty sky contain thousands of galaxies.
- It contributed decisively to the extragalactic distance scale and to the discovery of cosmic acceleration.
The mirror, and the recovery
Hubble launched in 1990 with a primary mirror ground to the wrong shape — an error of about two micrometres at the edge, traced to a miscalibrated test instrument. The result was spherical aberration that blurred every image, and it was a serious institutional failure as well as a technical one.
The 1993 servicing mission installed corrective optics that compensated for the error, and later instruments incorporated the correction internally. The recovery is often cited as the strongest practical argument for serviceable spacecraft, and it is the reason Hubble's design philosophy is discussed alongside JWST's unserviceable one.
Why servicing mattered so much
Five shuttle servicing missions between 1993 and 2009 replaced instruments, gyroscopes, batteries and solar arrays. The detectors flown in 2009 were generations beyond those launched in 1990, so the observatory's capability increased over its lifetime rather than declining.
No comparable capability now exists — the Space Shuttle was retired in 2011 — so Hubble operates on its existing hardware, managing gyroscope failures with reduced-gyro observing modes, while its orbit gradually decays. It is a reminder that the servicing option was a product of a specific era.
The deep fields
In 1995 Hubble was pointed at an apparently empty patch of sky in Ursa Major for roughly ten days. The resulting Hubble Deep Field contained several thousand galaxies in an area a small fraction of the full Moon's apparent size, at a wide range of distances and cosmic epochs.
It was a deliberate use of scarce observing time on a target with no known content, and it produced one of the most consequential images in the history of astronomy. Later deep and ultra-deep fields extended the technique, and the approach — stare long enough at nothing and find everything — has since been repeated by other observatories including JWST.
What it measured
- Cepheid variables in distant galaxies, refining the extragalactic distance scale and the value of the Hubble constant.
- Type Ia supernovae at high redshift, contributing to the 1998 discovery that cosmic expansion is accelerating.
- Direct evidence for supermassive black holes in galaxy centres through stellar and gas dynamics.
- Exoplanet atmospheric composition through transmission spectroscopy, before JWST extended the technique.
- Ultraviolet observations, a range JWST cannot cover at all, which remains a distinctive Hubble capability.
Continue in the data
Catalogues, hubs, and reference pages that hold the underlying records for this topic.
Frequently asked
- What was wrong with Hubble's mirror?
- It was ground to slightly the wrong shape — an error of about two micrometres at the edge, caused by a miscalibrated test instrument during manufacture. The resulting spherical aberration blurred every image. A 1993 servicing mission installed corrective optics that compensated for the flaw, and later instruments built the correction in.
- Can Hubble still be repaired?
- Not with current capability. All five servicing missions were flown by the Space Shuttle, retired in 2011, and no operational vehicle is equipped for the task. Hubble continues on its existing hardware, managing gyroscope failures with reduced-gyro observing modes, while its orbit slowly decays.
- What is the Hubble Deep Field?
- An image assembled from roughly ten days of exposure in 1995 on an apparently empty patch of sky in Ursa Major. It revealed several thousand galaxies in an area a small fraction of the full Moon's apparent size, spanning a wide range of distances and cosmic epochs — a deliberate gamble with scarce observing time that became one of astronomy's most consequential images.
- Has JWST made Hubble obsolete?
- No. They observe different wavelengths. Webb is optimised for infrared and reaches ranges Hubble cannot; Hubble covers ultraviolet and visible light, where Webb has little or no capability. Ultraviolet observation in particular remains a Hubble-only capability among major space observatories.