IT is difficult to overstate the intensity of the excitement among the world's astronomers. This week 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 lead not just 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 around 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.

For centuries this oldest of the sciences has been derided 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 Earth'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.

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.

NGC625 1 - 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 to form a galaxy of young stars.

But what is exciting astronomers most are the pictures this week of the galaxies at the edge of the universe. They have come to us 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.

"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 result will not simply be a remapping of the detail of the universe. It will mean a shift in paradigms, too, and 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 to be 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.

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 Prof Longair. "Between the two we're getting towards a chronology of what happened in the history of the universe. That has to be much more exciting than mere theory."