Benchmarks: Double vision

Construction of two of the world's largest telescopes has begun. The Gemini telescopes will be sited in Chile and Hawaii. Groundbreaking commenced at Mauna Kea, an extinct volcano on Hawaii, following a blessing by a Hawaiian religious leader to placate Pele, the volcano goddess.

The twin 8.1m telescopes, costing pounds 120m for the pair, should provide images 10 times more sensitive than on existing telescopes.

Astonomers hope that the Gemini telescopes will help them answer puzzles such as the origin of planets, stars, galaxies and the chemical elements.

The improved optical systems in the telescopes will also avoid the twinkling effect of stars caused by the atmosphere and will provide clearer images than the Hubble Space Telescope.