The William Herschel Telescope (WHT) is the largest UK owned telescope in the Canary Isles, and indeed throughout the northern hemisphere. It was built during the 1980's and first saw operation in 1987.

With a mirror width of 4.2 metres, it was amongst the largest telescopes in the world when first built, however, manufacturing improvements over the past 20 years have seen much larger telescopes relegate it to a medium-size telescope. That said, the WHT has some state-of-the-art instrumentation, and still produces world class science.

Some facts about the telescope:

• Observatory location: La Palma, Canary Isles
• Height above sea level: 2,332 metres (7,650 feet)
• Moving Mass: 210 metric tonnes
• Mirror diameter: 4.2 metres

This magnificant telescope is housed in a purpose built enclosure. Because the telescope is so complex, it requires engineers and scientists to be available in case any of the systems break. As such, an attached building is needed to house offices, workshops, toilets etc. This is the main reason why the telescope enclosure is so large.

The observatory building also contains an aluminising plant which is used to replace the mirror's reflective surface every couple of years. Over this period, dust and other contaminants reduce the mirror's reflectivity, lowering its performance and hence the light gathering power of the telescope.

The control room is the nerve centre of the observatory. Each evening astronomers make their way to this room, and spend all night here as they observe various objects throughout the Universe.