When Galileo constructed his first telescope in the early years of the 17th Century, it allowed him to record the phases of Venus, to pick out spots on the surface of the Sun, and to discover the four moons of Jupiter that would later take his name.
But no early Italian genius of astronomy could ever have conceived of the images that today's most famous telescope have given us. Since the space shuttle Discovery left it dangling in the heavens on 24 April 1990, Nasa's Hubble Telescope has produced unfathomably beautiful photographs of expanding supernovas six light years wide; thousands-strong clusters of stars held together by their own gravity; far, far away galaxies resembling deep-sea creatures; echoing black holes and vast, glowing clouds of hydrogen gas, floating somewhere out in the dark.
Hubble has shown us that space is everything that we – or David Bowie, or Pink Floyd, or Stanley Kubrick, or George Lucas or, indeed, Galileo himself – always imagined it might be. The images of the universe that it has beamed back to Earth in its two decades aloft have validated and outstripped Star Trek, a thousand prog-rock LP covers, even that speech of Rutger Hauer's from the end of Blade Runner about "attack ships on fire off the shoulder of Orion." As far as we ignorant masses are concerned, its discoveries have turned science fiction into scientific fact.
The Hubble telescope was named after astronomer Edwin Hubble, who died in 1953, 37 years before its eventual launch. Yet like the contraption christened in his honour, he was responsible for a profound shift in our understanding of the universe: Hubble not only proved that other galaxies existed beyond our own Milky Way, but also contributed to the scientific dialogue that discerned those galaxies moving away from each other. In short, he showed that the universe was expanding – a phenomenon that his technological namesake would later observe with unerring clarity. There were other space telescopes before Hubble, but its range and versatility made it the most admired satellite in the sky, and transformed the public image of astronomy.
The renowned astrophysicist Lyman Spitzer first proposed the notion of a space-based telescope as early as 1946, though it took a further 40 years for Hubble to be agreed upon, designed, named and primed for launch. After the space shuttle Challenger crashed in 1986, it was postponed for a further four years. When Hubble was finally sent into orbit, after decades of frustration and delay, a flaw in one of the mirrors crucial to its operation left it unable to operate to its full capacity. Yet a visit by a team of space-walking repairmen three years later restored its intended capabilities. The telescope's longevity is due to its being the only space telescope ever designed to be maintained in space by visiting astronauts. Four more teams of Nasa technicians have returned to Hubble since 1993, the last of them in 2009. That final MOT will allow the telescope to continue serving up wonders until 2014, when it will be replaced by its hi-tech successor, the James Webb telescope.
Hubble has found black holes at the core of every galaxy in its range. Based on calculations made by Edwin Hubble, it has helped scientists to clarify the age of the universe based on its rate of expansion – and demonstrated that it is picking up speed. Many light years closer to home, it took crystal clear pictures of the comet Shoemaker-Levy 9 crashing into the gaseous surface of Jupiter in 1994, teaching Nasa's astronomers valuable lessons about both planet and comet. These were discoveries that could never have been achieved using ground-based equipment.
Nasa polled internet users in 2001, asking which astronomical phenomenon they would like the telescope to study next. They chose the Horsehead Nebula, a dark cloud that hangs from Orion's belt, some 1,500 light years from Earth. The organisation has made sure to maintain the public's interest in Hubble by releasing high-quality reproductions of its most striking images, like those on these pages, for the Hubble Heritage Project. If ever science and art could be shown to overlap, it is in these pictures.
What looks like a face nestling from the cold in a thick fur jacket is actually a dying star, nicknamed – for obvious reasons – the Eskimo Nebula. What looks like delicate, rainbow-coloured mist to you and I in fact represents a dying star with a surface temperature of 200,000C (35 times hotter than the Sun), 3,500 light years away in the Bug Nebula, behind a cloud of dust and ice.
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