The London Planetarium has been a landmark since its construction in 1958. Thousands of audiences have enjoyed relaxing under perfect night skies as soothing voices revealed the secrets of the universe.

But this year a dramatic transformation took place beneath the familiar green dome. After a six-month refit the planetarium reopened with its own entrance, remodelled auditorium and new interactive exhibition. However, the most fundamental change has been at the very heart of the planetarium. Gone is the venerable Zeiss projector: Digistar has arrived.

Traditional projectors like the Zeiss focus tiny beams of light on to the dome to make the stars. Digistar uses electronics to create its effects. A cathode ray tube and optical system throw images on to the dome: computer graphics generate the starfields and much, much more. The computer can create wireframe images of almost anything. We can travel through cities, galaxies and the human brain or watch spacecraft tumble among the planets.

The most exciting feature, unavailable using conventional projectors, is the ability to travel through space in three dimensions to vantage points anywhere in a 900 light year radius of the sun. Digital technology has created a whole new genre of planetarium show - it is Star Trek in virtual reality.

Digistar is accompanied by a sophisticated slide and video array which can portray 360 degree landscapes and all-sky scenes which fill the dome. Backing this visual feast is a superb wrap-around audio system which moves narration around or floods the auditorium with sound. The differences between old and new are immediately striking. The new entrance disentangles planetarium-goers from the queues for Madam Tussaud’s and there is wheelchair access throughout.

The inaugural presentation is Cosmic Perceptions. The rich tones of Ian McKellen provide the narration with versions available through earphones in four other languages. Beginning with sunrise over Stonehenge, Cosmic Perceptions takes us through the development of our vision of the universe.

Digistar follows light through the eye into the synapses of our brain and to the limits of space to show us strings of galaxies. Familiar constellations decorate the night sky only to distort and disintegrate as we leave Earth on a trip through the galaxy.

Digistar has its drawbacks. Its monochrome images cannot depict star colours and the stars seem to be less crisp than those produced by its mechanical predecessor. But it indicates how multimedia will transform the planetarium experience. It will be fascinating to see how the talented staff at London Planetarium exploit the power of their remarkable new instrument.

Outside the auditorium it is well worth lingering in the three-tier exhibition. Launch Zone features astronauts and astronomers while Space Zone explores aspects of deep space. Most impressive is Planet Zone with its magnificent scale models of planets, touch screen video and data files. The popular schools’ programme recommences this term: education packs are now available.

The refurbishment has been both radical and (at a cost of Pounds 4.5 million) expensive. With it London Planetarium has guaranteed future audiences a memorable insight into the wonders of astronomy.

* The London Planetarium, Marylebone Road, London NW1 5LR. Tel: 0171 486 1121.