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Herschel, the space observatory

Nearly 1.5 million kilometres away from the Earth is the European Space Agency’s Herschel Space Observatory, the largest space telescope ever launched. Thanks to its 3.5-metre diameter telescope mirror, it can collect light from the full far-infrared and submillimetre waveband, meaning it allows astronomers to see the most-distant stars and galaxies, the ones that Earthbound telescopes are simply unable to see.

Facts & figures

Height: 7.5 metres

Width: 4 metres

Weight: 3,300 kilogrammes

Orbit: Lissajous orbit around Lagrange point L2 (situated 1.5 million kilometres from Earth in the opposite direction to the sun). Herschel’s average distance from L2 is 800,000 kilometres;


What will it do?

Across the Milky Way are massive clouds of dust and gas. When conditions are right, some of these clouds collapse and eventually form new stars. (Our sun was created this way.) Unfortunately for astronomers, it is exceptionally difficult to see these newly born stars due to the clouds that surround them and only when the dust disappears do they become visible. The Herschel Space Observatory collects infrared light emitted by stars, light that passes through these clouds of dust, allowing astronomers to see inside and study the birth of stars, something until now impossible.

Herschel will also investigate the formation and evolution of galaxies billions of light years away by picking up the infrared radiation emitted by their hot nascent stars. This light has also, until now, been invisible to astronomers because it is absorbed by the Earth’s atmosphere.


Why call it Herschel?

Sir William Herschel, born in Hanover, Germany, in 1738, was one of the most innovative and successful astronomers of all time. Originally a musician and composer, he moved to London in 1757. In 1766 he moved to Bath in south-west England to take up a job as organist at the Octagon Chapel. It was there that he first became interested in astronomy and began experimenting with constructing his own mirrors and telescopes. In 1781, using one of his own telescopes and aided by his sister Caroline, he discovered the planet Uranus – the first planet detected since ancient times. This brought him overnight fame and he was awarded a salary by the king, which allowed him to dedicate himself to astronomy full-time.

In 1800, he turned his attention to light and performed a simple experiment, the results of which explain why the Herschel Space Observatory bears his name. He used a prism to split light into its constituent colours and using a thermometer took each one’s temperature. He discovered that the hottest light was the ‘invisible’ one, which he called ‘calorific rays’ – what is today known as infrared radiation, the light that Airbus Defence and Space’s mirror collects to produce its remarkable images of deep space.

When William Herschel died in 1822, he left behind a series of discoveries that changed the way space was seen. As well as his discovery of Uranus, he proved that nebulae were indeed groups of individual stars – many believed at the time that their milky appearance was due to a strange cosmic liquid – and observed 2,500 nebulae and star clusters, as well as two moons of Uranus, Titania and Oberon, and two of Saturn’s moons, Mimas and Enceladus. These last two moons he found using the world’s largest and most powerful telescope – it had a 122-centimetre mirror and focal length of 12 metres – one he had built himself in 1789 thanks to a £4,000 grant from King George III.


HerschelSpace Telescope