In a faraway corner of the universe ...

It is difficult to overstate the intensity of the excitement among the world's astronomers this week. Yesterday yet more images of distant galaxies began to coalesce on their computer screens - the products of the latest remarkable photographs sent back to Earth from the Hubble Space Telescope.

They are pictures the like of which no one has ever seen before. They will not just lead to a remapping of the universe. They will also cast new light on the nodal questions which have for generations preoccupied practitioners of astronomy. Did the Big Bang really happen? How are stars born? How do they die? How did the galaxies take shape? How fast are they expanding and, therefore, how old is the universe?

The answers to those momentous questions are becoming clearer. Already the Hubble team have concluded that the universe is a lot younger than had been supposed. Now they are edging towards more ambitious issues. Are there planets round other stars in other galaxies? With what they now estimate to be 400 billion galaxies in existence they have even begun to talk about life in outer space.

"It's been like taking off sunglasses and picking up binoculars," said Dr Robin Catchpole, research astronomer at the Royal Greenwich Observatory and one of the few Britons to work direct with Hubble.

For centuries this oldest of the sciences has been derided - perhaps unfairly - for its lack of hard data . Hubble has changed all that. For the first time they have extensive hard facts against which to check their theories and discover whether the fine details of notions like relativity are correct.

Why has this been so? "Looking at the stars from Earth is like looking at the sky from under water," said Dr Heather Couper, the Gresham Professor of Astronomy. "The Earth's atmosphere wobbles and distorts everything you look at."

Not for Hubble, orbiting 600 kilometres above the planet's surface. In the six years since it was launched it has sent back thousands of stunning images. Even in the early years, when it was operating on a defective mirror, it was beaming back images of a far greater clarity than anything that could ever be seen with the existing technology on Earth.

When Hubble was launched in 1990 the reflecting mirror in the telescope contained an error introduced by the lens grinders - these producers of US military spy satellites were so obsessive about security that they refused to allow their government's own space agency, Nasa, to take part in the process. The resulting error - of only one ten thousandth of an inch - produced a telescope that was in effect astigmatic.

But since 1993, when Nasa astronauts corrected the fault during the longest and most expensive space walk ever conducted, Hubble has produced a stream of images that are unparalleled in the history of science.

All have enthralled the world's scientists. Pictures of the Comet Shoemaker- Levy as it hit Jupiter. Close-ups of storms on Saturn. The astonishing Supernova 1987A with its loops and rings of gas. The vision of M87, a giant galaxy with, at its centre, what appears to be a massive black hole the size of 3,000 million suns. NGC6251 - unpoetically named because those who located it thought it too far off to ever need anything more than a mere number - a great disc of gas swirling into a black hole. Images of "gravitational lenses" - banana shaped galaxies which bend light just as Einstein had predicted in 1915.

Perhaps most spectacular was the Eagle nebula - a massive "stalagmite" of dust and gas in the constellation Serpens, 42 million billion miles away. Hubble's Wide Field and Planetary Camera caught a striking image of vast columns of cool gas and dust - dense enough to collapse under its own weight to form a galaxy of young stars. "They are structures that you never knew existed and you have to find ways of explaining," said Heather Couper with unbridled enthusiasm.

But what is most exciting astronomers is the pictures this week of the galaxies at the edge of the universe. They have come to us across the light years in the appearance they had adopted near the beginning of time.

Until now astronomers have had problems understanding how galaxies formed. "Before we had the model of the Big Bang, the formation of the elements and then ... a big gap before the formation of galaxies," said Dr Catchpole. "We really didn't know how all that started." Hubble is now filling that gap. "That's where the biggest excitement is."

"It is a big revolution in our understanding of the distant galaxies," said Dr Malcom Longair, Jacksonian Professor of Natural Philosophy at the Institute of Astronomy at Cambridge. "We're able now to identify many distant galaxies at a point when the universe was less than a quarter of its present age. And what we are seeing runs counter to many of the favoured theories - such as the Cold Dark Matter theory of how galaxies form, which concludes that most of the major systems are forming only now. It's an absolutely key piece of information in cosmology."

The Hubble telescope is named after the US astronomer Edwin Hubble who, using a 100-inch telescope - which then, in 1917, was the most powerful in the world - first looked at galaxies in a detailed way and worked out that the universe was expanding.

In the years that followed the pioneering work in astronomy shifted away from such optical instruments. Instead of using light technology switched to other forms of radiation - infra-red, ultra-violet, X-ray. Nigel Henbest, the writer and broadcaster on astronomy who is currently researching a major TV programme for Pioneer Productions on the Hubble, uses the analogy of a piano to explain the shift: "On a piano keyboard optical telescopes would represent only the few notes around Middle C; the other forms of radiation allow us to hear the whole range from low notes to very high - enabling us to hear the whole symphony of the universe."

In the 1960s radio telescopes showed up giant explosions or concentrations of energy - quasars (galaxies that are blowing apart) and pulsars (which are the highly compacted corpses of dead planets). In the 1970s X-rays showed gas swirling around and disappearing down what were later identified as black holes. In the 1980s infra-red cut through the dense clouds of gas and dust that surround the birth of stars, which are hidden from optical telescopes. It seemed as if the day of the telescope that operated like the human eye was over.

But then came the idea of launching one to orbit above the distortions of the Earth's atmosphere. It was not a new thought. The US astronomer Lyman Spitzer proposed it in 1946 but the only rockets around then were V2s and it was 11 years before the first satellite, Sputnik, entered planetary orbit. When the technology (and political will) caught up with the vision the results were everything Spitzer could have hoped for.

The result will not simply be a remapping of the detail of the universe. It will mean a shift in paradigms, too. Some theories look to be confirmed. "Scientists were 90 per cent sure that black holes existed," said Nigel Henbest. "Since Hubble they are 99.9 per cent certain."

But there could also be profound changes. "One of the major problems Hubble has set out to solve is the calibration of distance in space," said Dr Catchpole. What will result - the Hubble Constant - "will calibrate the scale of the universe in terms of physical units. If we can tie down the distance scale we can move ahead a lot; we may even have to revise our physics."

Already scientists are having to face up to the post-Hubble consequences of the universe being younger than had been supposed. Previously they thought it between 12 and 15 billion years. Now 10 billion seems more likely. "We may have to look again at the whole theory of the origin of the universe," said Dr Catchpole. "It would be very exciting if we had to have a fresh look at the Big Bang theory."

The repercussions of Hubble are hard for the lay reader to comprehend. "It has impacted on all fields," said Professor Longair, who is also chairman of the Space Telescope Science Institute in Baltimore, which runs the Hubble project. "There is no aspect of astronomy that hasn't been touched. What we're learning is the sort of physics that is needed to understand the large-scale structure of the universe and how we all came about."

So what else might Hubble reveal? The nominal life of the orbiting telescope is 15 years. That would take it up to the year 2005. In practice Nasa - which funds 85 per cent of the $1.4bn project, with the European Space Agency forking out the other 15 per cent - will keep it going as long as they have maintenance funding.

There is a plan to send a Space Shuttle team to Hubble in 1997 to install a parallel infra-red camera that will allow astronomers to see inside the stellar nurseries of the Eagle and Orion nebulae.

"The optical telescope is showing the younger galaxies forming; infra- red will show the older already-formed ones," explained Professor Longair. "Between the two we're getting towards a chronology of what happened in the hostory of the universe. That has to be much more exciting than mere theory."

"One of the things we hope for is evidence of planetary systems," said Dr Catchpole. That is astronomer-speak for the possibility that with planets will come some form of life.

The universe may contain up to 400 billion galaxies, one Nasa scientist pointed out this week. "If only 1 per cent of the stars have planets and only 1 per cent of them have life ... well, you can draw your own conclusions," he said portentously. British astronomers prefer to be more circumspect. But suddenly nothing seems impossible.

A FANTASTIC VOYAGE

April 1990 After 10 years of preparation, and many delays, the Hubble telescope is launched into a low orbit by the Space Shuttle Discovery.

July 1990 As the first pictures are sent back, it becomes apparent that the telescope is afflicted by a focusing flaw, rendering the major on-board camera, the Wide Field Planetary Camera (WFPC), virtually useless. A subsequent Nasa investigation puts it down to an error in the grinding and polishing of the main mirrors.

September 1990 The first images taken by Hubble's Faint Object Camera (FOC) - of a supernova, a star cluster and a quasar - become available. The photographs are impressive, in spite of the telescope's optical deficiencies.

July 1991 Observations of the core of the distant star cluster 47 Tucanae, made with the FOC, provide new evidence that stars may collide and capture each other and become revitalised in the process.

April 1993 The European Space Agency announces that the US Shuttle Endeavour will embark on a maintenance mission to Hubble that December.

December 1993 The Space Shuttle Endeavour successfully undertakes an 11-day mission to fit Hubble with corrective optics and to replace damaged solar panels.

May 1994 Hubble discovers a whirling spiral disc of ultra-hot gas rotating at 1.2 million mph, providing firm evidence of the existence of black holes (essentially collapsed stars that create fields of extremely strong gravitational pull)

July 1994 Hubble detects the presence of helium in the primordial universe, confirming a critical prediction of the Big Bang (the explosion of a small, dense mass of gas which some scientists believe to have constituted the birth of the universe). Later in the month the collision of the comet Shoemaker- Levy 9 with Jupiter is observed, prompting speculation that the Earth could one day be subject to a similar onslaught from space.

June 1995 Hubble identifies the birthplace of the comets on the fringes of the Solar System, the images suggesting that there are at least 200 million comets orbiting the Sun in a belt that lies beyond the orbit of Neptune and engulfs that of Pluto.

January 1996 Hubble sends back pictures from the edge of the universe. They show far- off galaxies as they were almost at the beginning of time.