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Herschel is the largest astronomical telescope ever launched. Its 3.5 m-diameter primary mirror is giving astronomers their best view yet of the Universe at far-infrared and submillimetre wavelengths.

The mission builds upon the legacy of ESA’s Infrared Space Observatory and subsequent infrared missions such as NASA’s Spitzer and JAXA’s Akari.

The telescope is named after the German–British astronomer William Herschel. In 1800 he discovered infrared radiation while studying the Sun. He also discovered Uranus, the seventh planet in the Solar System, and surveyed the sky.

The Herschel mission has an unprecedented view of the cold Universe, bridging the gap in the spectrum between what can be observed from the ground and earlier space missions of this kind. Infrared radiation can penetrate the gas and dust clouds that hide objects from optical telescopes, allowing astronomers to see deep into star-forming regions, galactic centres and planetary systems.

Cooler objects, such as tiny stars and molecular clouds, and even galaxies enshrouded in dust (which barely emit optical light) are visible in the infrared. It can even detect emissions from dust itself. Observing in the infrared provides us with a complementary view of the Universe.

But why go into space to do this? The simple reason is that Earth’s atmosphere blocks most infrared wavelengths. In addition, the atmosphere produces its own infrared radiation. So, observing in the infrared from the ground is like trying to view stars on a cloudy day.

Herschel was launched together with ESA’s Planck satellite. Since operations began, the two missions have been studying different aspects of the cold cosmos.

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