Mighty telescope to see again

Heyday: The telescope was once the world's largest

By BBC News Online Science Editor Dr David Whitehouse

What was once the world's largest telescope will soon be able to make observations of the night sky again.

The so-called Leviathan is to be fitted with a new mirror and will look once more at the stars and galaxies it first saw over a hundred years ago.

It was a telescope ahead of its time. It was built in 1845 by the Third Earl of Rosse in the grounds of his castle near the Irish town of Birr.

The tube of the telescope was suspended between two walls and it took four people to pull at the ropes to move it as the Earl, perched on ladders, looked through the eyepiece.

Between 1845 and 1914, the Leviathan was the largest telescope in the world and attracted astronomers from all over the globe.

Spiral galaxies

Perhaps its most famous observation was that of the M51 galaxy. At the time, it was thought to be just a cloud of gas and dust.

The original mirror

But the observations made with the Leviathan showed a curious spiral structure within it. It was the first hint at the spiral structure of galaxies that we now take for granted.

The telescope was so far ahead of its time that even into the 1970s, its mirror could still claim to be one of the largest ever made.

The original mirror was made of a metal alloy called speculum. However, it tarnished quickly and had to be removed and polished frequently.

It was not until the 1850's that the silver on glass mirrors used today were developed. In 1914, the telescope was dismantled and it became a sorry ruin. The mirror was sent to London's Science Museum where it can still be seen.

Largest in Europe

The telescope tube was lain on its side and there it remained, derelict, until 1979 when it was renovated.

Now it is to have its eye back. Within weeks, Birr will be restored to the status of a fully functional telescope with the installation of a new mirror.

The original mirror took two years to make. Its replacement has occupied University College London engineers for 18 months. They have just completed the mirror and it is currently undergoing its final tests prior to delivery to Birr castle.

After its has been installed, it will have its "first light" and it will become the largest telescope in Ireland.

But one mystery remains: the location of an original reserve mirror used when the other reflector was being polished. It has been lost.

"It is a mystery," says Alicia Parsons of Birr castle. "It weighed three tonnes, so it would not have been easy to lose."

In the making: The new Rosse mirror