Hubble - the telescope that transformed astronomy
Sen—Way back in 1990, a telescope was launched into space to bring us new views of the heavens. Astronauts aboard the shuttle Discovery released this valuable new astronomical tool from the spacecraft’s cargo bay in an orbit high above the Earth.
The Hubble space telescope, with a two-meter wide mirror to collect starlight, was only about the size of an average professional telescope on the ground. But free from the distorting effects of our atmosphere and bad weather, and viewing in eternal darkness, it promised to deliver exciting new results for astronomers.
Today it is clear that Hubble has not only been a powerful research tool, exploring the universe almost back to its beginnings, but it has also been a powerful ambassador for astronomy, exciting the imagination of ordinary people all over the world.
The idea for a telescope in such a perfect location was formulated by noted astronomer Lyman Spitzer way back in 1946, though a German rocket scientist, Hermann Oberth had suggested the idea even earlier in 1923. NASA's plan for the Large Space Telescope as it became known were approved in 1977 and it was later named after ground-breaking astronomer Edwin Hubble who first proved in the 1920s that our Milky Way was just one island galaxy in a vast and expanding universe. Spitzer later received recognition of his own work when another NASA space telescope was given his name.
Hubble's birth was not painless. There were long delays in getting it built as politicians tried to cancel it and then the Challenger shuttle disaster in 1986 grounded the space fleet that would put it in orbit around the Earth. But finally, on April 25, 1990, the shuttle Discovery soared aloft, with current NASA Administrator Charles Bolden among the crew, carrying the precious telescope into the heavens. They released it into an orbit nearly 560 km up (347 miles).
The telescope, a reflector of Ritchey-Chrétien Cassegrain design, is 13.3 meters long and its "eye" is a single primary mirror 2.4 meters wide (94.5 in). Solar panels provide the power it needs to function, and it uses special sensors to lock on to guide stars when it turns in space to pinpoint its targets.
As soon as the telescope began sending pictures back to Earth, astronomers realised to their horror that there was a serious problem with the telescope. A tiny error in shaping the curve of the primary mirror meant images were not sharp but blurred. The blunder threatened the project with disaster. But with classic ingenuity, the Hubble engineers came up with a correcting lens, rather like an equivalent of spectacles, which were fitted by astronauts on the first servicing mission to Hubble, by the shuttle Endeavour, in December 1993.
Four further shuttle flights were carried out to service Hubble, update instrumentation and keep it functioning until 2014 at least. Eventually it will be brought out of orbit, probably to a fiery demise in the atmosphere unless there is the will and ability to preserve it to be carried home one day to a place in a museum.
Dr Heidi Hammel is a leading planetary scientist who has worked extensively with Hubble and is now helping prepare its successor, the James Webb Space Telescope. She told Sen: "My first programme with Hubble was when Comet Shoemaker-Levy 9 was crashing into Jupiter. I was a young astronomer, fresh out of my post-doc, and I got to watch this amazing event.
"Hubble has done a terrific job on getting astronomy out there for everyone to see. It has been so powerful in reminding people that there is a big universe out there, thanks to iconic pictures such as the Eagle Nebula's Pillars of Creation.
"When you see those images it really makes you take a little step back by providing a different perspective on the world. It reminds you that there's a whole lot more out there than just getting stuck in a traffic jam or picking up your dry cleaning."
The Hubble Space Telescope in orbit. Image credit: NASA
Hubble currently carries a number of instruments to produce its valuable results.
The Wide Field Camera 3 sees the universe in near-ultraviolet, visible and near-infrared light and operates in higher resolution than the other instruments and with a wider field of view. Its targets include dark energy, dark matter, star formation and distant galaxies.
The Cosmic Origins Spectrograph only views ultraviolet light analysing the chemical make-up and nature of faint objects with great sensitivity.
Hubble's Advanced Camera for Surveys looks at visible light to study, in particular, the origin and evolution of the most distant galaxies in the universe.
The Space Telescope Imaging Spectrograph views in ultraviolet, visible and near-infrared light, and a speciality is locating black holes. Other targets include stars, quasars and galaxies.
Lastly, the Near Infrared Camera and Multi-Object Spectrometer is sensitive to the hotspots of the universe, peering into interstellar dust clouds to image the sites where stars are being born.
Hubble's views of the heavens have extended from detailed close-ups of the planets to ancient galaxies as they looked billions of years ago. Among the most memorable are:
In the Solar System:
Martian weather; aurorae on Jupiter; the rings of Uranus; discovering Pluto's moons; watching the impact of Comet Shoemaker-Levy 9 on Jupiter; and measuring the size of icy new worlds in the Kuiper Belt beyond Neptune. In 2014 it identified potential targets for NASA's New Horizons spacecraft to visit after it shoots past Pluto.
In our own galaxy:
Stellar nurseries in the Eagle Nebula (the famous Pillars of Creation image) and the Carina Nebula (a picture taken to mark Hubble’s 20th anniversary); planets forming in the Orion Nebula; supernova remnant the Crab Nebula with its central neutron star; an image of an exoplanet orbiting the star Fomalhaut; the detection of methane in another exoplanet's atmosphere; and pictures of shells of gas forming so-called planetary nebulae which show how stars like the Sun will die.
Beyond the Milky Way:
Following up Gamma Ray Bursts; the universe's biggest explosions, caused by the collapse of massive stars or collision of neutron stars; plus the aftermath of a supernova explosion in the Large Magellanic Cloud; discerning individual stars on the outskirts on neighbouring galaxy M31 in Andromeda; weighing supermassive black holes at the heart of other galaxies; observing cepheid "distance markers" in the galaxy M100 mapping dark matter; finding clues for mysterious dark energy; studying active galaxies called quasars; measuring the expansion of the universe and imaging the Hubble Ultra Deep Field—a remarkable photo showing thousands of galaxies in a minute patch of sky as they were a few hundred million years after the Big Bang.
Though Hubble is becoming advanced in years, it is performing some of its most challenging and important research ever.
One survey called CANDELS (Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey) is its largest project ever and aims to discover how galaxies evolved in the early Universe, by imaging 250,000 galaxies in five different directions.
To carry out this census of galaxies between 13 billion years old, when they first appeared, and nine billion years old, Hubble is combining the power of its latest infrared camera, the Wide Field Camera 3 (WFC3), and its Advanced Camera for Surveys (ACS). The survey covering the first third of the Universe's life requires around three and a half months of telescope time, spread over two to three years.
Another major project is commonly known as the Frontier Fields program and combines Hubble's observations with those of two other NASA observatories in space, the Spitzer Space Telescope and the Chandra X-ray Observatory.
The program is detecting the most remote and early galaxies in the Universe by finding their images as naturally magnified by gravitational lensing, the effect produced by massive objects lying in the foreground, between Hubble and the distant galaxies.