As Hubble reaches the autumn of its life, astronomy is looking to the future with a new batch of telescopes. Simon Singh outlines advances in the field

Astronomy is a unique discipline. Astronomers cannot touch a star, taste a black hole, listen to a supernova or smell a galactic cluster. They can merely look. Everything we know about the deep universe is based on the light that reaches the Earth, and our knowledge is limited by the power of our telescopes.

Astronomers are building a new generation of telescopes that will allow them to see objects that have previously been too faint to be detected. Seeing distant objects is equivalent to looking back in time, so astronomers will be able to refine their models of the early universe.

There are numerous telescopes, some already operational, that will push back the boundaries of visibility. The Hubble Space Telescope stands head and shoulders above other projects. Since its deployment in 1990, it has made the headlines because of the images that it has captured, made possible by its position above the Earth's hazy atmosphere.

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In March 2002, Hubble will receive its fourth and final maintenance visit, which should allow it to continue sending pictures for another decade. Meanwhile, plans are under way for other space telescopes, including the Next Generation Space Telescope, to be launched in 2007.

It is important to remember that ground-based telescopes still make significant contributions to astronomy. A telescope's power largely depends on the diameter of its mirror, which determines the amount of light it can gather. The Space Telescope has a mirror that is 2.4m across, which means that it can detect objects that emit as much light as a glowing cigarette in India as observed from London. However, the European Very Large Telescope (VLT) will have a mirror equivalent to 16m in diameter when it becomes fully operational later in the decade. It would be prohibitively expensive and risky to put such a large mirror in space.

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Sited in the Chilean desert, on a mountain above much of the atmosphere, the VLT will outperform the Space Telescope. This is partly due to adaptive and active optics, which allow astronomers to compensate for the blurring caused by a turbulent atmosphere and to correct for deformations in the mirror caused by its own weight and thermal expansion. The VLT will have several objectives, such as observing low-mass stars and brown dwarfs, studying the surface of stars and staring at the centre of our galaxy, seeking evidence of a black hole.

Astronomical bodies emit energy across a range of wavelengths, and only a fraction of it will be in the part of the spectrum visible to the human eye. The remaining energy consists of infrared, radio waves, X-rays and other forms of light. Some objects that emit only a tiny amount of visible light may emit enormous quantities of radio waves. Or the object may emit a range of wavelengths, but the visible light might be absorbed by dust clouds, while the infrared light may pass through easily. Therefore, it makes sense to look at wavelengths beyond the visible part of the spectrum. This may mean that ground-based observations are impossible.

For example, infrared light is absorbed by moisture in the atmosphere. While infrared telescopes in space are one solution, an intermediate approach is Nasa's Stratospheric Observatory for Infrared Astronomy (Sofia), a 2.5m telescope mounted in a Boeing 747 that will fly above 99 per cent of the atmospheric moisture. From 2002, it will observe the Sun, our neighbouring planets and their moons, comets, asteroids, stars and galaxies. Part of Sofia's function will be to relay images to classrooms.

Another telescope that can operate only above the atmosphere is Planck, a satellite due to be launched in 2007. It will measure the so-called cosmic background radiation field. When the universe was 1 million years old, the ambient radiation had cooled so much that it no longer interacted with the atoms that had been formed. The radiation has, in effect, not been altered for 10 billion years, so its current distribution and intensity reflect the features of the early universe.

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In 1992, the Cosmic Background Explorer (Cobe) published an image that showed the first detailed map of the background radiation. The map indicated tiny fluctuations, about 1 part in 100,000, in the level of radiation from different regions of the sky. The fluctuations were remnants of the earliest structures in the universe, which developed into stars and galaxies.

The Cobe measurements confirmed the broad Big Bang model, but they did not differentiate between sub-theories. For example, what caused the differences in levels of radiation? Some argue that the radiation fluctuations are the result of quantum fluctuations, others prefer a theory based on so-called topological defects. The Planck satellite should generate a detailed enough map of the radiation to settle the argument.

There are strong British contributions to the Planck mission. However, over the past decade, British involvement in such projects has declined steadily due to lack of funding. Sir Martin Rees, the astronomer royal, has repeatedly expressed concern that the UK, once the most powerful force in European astronomy, is falling behind.

The point of astronomy is to understand the universe. Nations fund astronomical research because it enriches civilisation.

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One positive sign is the government's support for UK membership of the European Southern Observatory, which already consists of eight nations and is running the VLT and other projects. This would certainly be a move in the right direction but even more support is required if Britain is to regain its previous level of excellence.

Simon Singh is a science journalist and author of Fermat's Last Theorem , The Code Book and The Science of Secrecy.

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