Hubble Space Telescope launch
Launched on 24 April 1990, the Hubble Space Telescope first disappointed with blurry pictures. After a 1993 repair it helped measure the age of the universe and revealed distant galaxies, and more than 35 years later it is still observing.
The story
On 24 April 1990 the Space Shuttle Discovery launched with the Hubble Space Telescope on board. The next day Hubble was released into an orbit about 610 km high. Its main mirror, which gathers the light, is 2.4 m across, and the telescope weighs about 11 tonnes. The idea of observing from above the shimmering air had first been proposed by the astronomer Lyman Spitzer in 1946, and it came true 44 years later.
Two months later, however, the first pictures came back blurry. The edge of the main mirror had been ground about 2.2 micrometres out of shape. That is only about a fiftieth of the width of a human hair, but it was enough to stop the light from coming to a sharp point, and the pictures smeared. For a while Hubble became the target of heavy ridicule.
In December 1993 astronauts from the Space Shuttle Endeavour visited Hubble to fix it. They installed a device called COSTAR that corrected the light, like a pair of glasses, and replaced a camera with a new one. After that, Hubble's pictures became remarkably sharp. Hubble had been designed so that astronauts could repair it and swap in new equipment in space.
Hubble was serviced five times between 1993 and 2009. Each time, parts such as cameras, the gyroscopes that help it point, and batteries were replaced. That is why Hubble is still observing more than 35 years after launch, and astronomers still ask for several times more observing time than it can give.
Mission goals
On the ground, telescopes see starlight smeared because the air above them moves, much like the way the view shimmers above hot asphalt on a summer day. Hubble sits above the air, so it can see far more sharply without that shimmering. Thanks to this, it has found black holes at the centres of galaxies, studied the atmospheres of planets around other stars, and discovered small moons of distant bodies in our solar system.
One of Hubble's biggest achievements was measuring the age of the universe more precisely. It looked for Cepheid variables, stars that brighten and dim on a regular schedule, in distant galaxies and used them to measure how far away those galaxies are. That revealed how fast the universe is expanding to within about 10 percent, which narrowed down the age of the universe a great deal. In 1998 its observations of distant supernovae helped with the discovery that the universe's expansion is speeding up.
In 1995 Hubble spent ten days photographing a tiny patch of sky in Ursa Major that looked empty. This became the Hubble Deep Field. About 3,000 galaxies showed up in that small patch. The picture showed at a glance that the universe is filled with far more galaxies than people had imagined.
Mission chronology and background
The mirror was ground wrongly because of the manufacturer's test equipment. One lens inside the device used to check the mirror's shape was 1.3 mm out of place. During manufacturing two other test instruments warned that something was wrong, but they were ignored on the grounds that they were less precise. The story is often told as a lesson never to dismiss small warnings.
The fifth and last servicing mission, flown by Atlantis in 2009, was once cancelled. After the loss of the shuttle Columbia in 2003 it was judged too risky. But pressure from scientists, the public and Congress brought it back. The Wide Field Camera 3 and the Cosmic Origins Spectrograph installed on that mission are still among Hubble's main instruments.
The James Webb Space Telescope launched in December 2021, but Hubble did not retire. Hubble mainly sees visible and ultraviolet light and Webb mainly infrared, so the two work as partners. In 2024 gyroscope problems forced Hubble to switch to using just one gyroscope, but it keeps observing. Hubble is slowly sinking because of drag from the thin upper air, and it is expected to fall into the atmosphere sometime in the 2030s.
Where to see it — sky and simulator
Hubble now circles Earth about every 95 minutes at a height of roughly 520 km. When it passes overhead around dusk or dawn it can be seen with the naked eye, moving like a bright star. Switch on satellites in the sky view to see when and along what path Hubble will pass over your location (satellite display is available to supporters and above).
You can also find the site of the Hubble Deep Field in the sky view. It lies near the handle of the Big Dipper, at right ascension 12h 36m and declination +62°. Zoom in and you will see that it is a dark patch with hardly any stars. In the 3-D interstellar view and the sky view's object list, you can find subjects of famous Hubble pictures, such as the Eagle Nebula, about 7,000 light-years away, and the Whirlpool Galaxy M51, about 23 million light-years away, at their real distances.
FAQ
Why were the first pictures blurry?
The edge of the main mirror was ground about 2.2 micrometres out of shape, so light did not come to a sharp point. A correcting device fitted in 1993 fixed it.
Can Hubble be seen with the naked eye?
Yes. When it passes overhead around dusk or dawn it looks like a bright moving star. The sky view's satellite display shows when it will pass.
How much longer will Hubble work?
There is no fixed date, but it is expected to keep observing into the 2030s. After that its orbit will sink until it falls into the atmosphere.
Does James Webb replace Hubble?
No. Webb mainly sees infrared light and Hubble visible and ultraviolet light, so the two work together as partners.
Related
- James Webb Space Telescope launch
- Roman Space Telescope launch
- Shoemaker–Levy 9 hits Jupiter
- James Webb — object index
Times and figures are approximate — verify with official sources when planning travel. Simulation uses J2000 mean elements.