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Herschel Overview

The Herschel Space Observatory is the fourth and final "Cornerstone" mission of the European Space Agency's (ESA) space science program. Initially called the Far Infrared and Sub-millimetre Telescope (FIRST), it was renamed in honour of German-born astronomer William Herschel, who discovered infrared radiation. The Herschel Space Observatory was launched on May 14, 2009 on board the same Ariane 5 rocket that carried Planck.

Over the next three years, Herschel will allow scientists to study the "cool Universe" and hope to learn about important astronomical questions ranging from how the first galaxies formed and evolved to how stars and planets form today. Because much of the Universe is too cold to emit light in the visible spectrum, Herschel will observe cold celestial objects by capturing the radiation emitted in the spectrum ranging from the far infrared to sub-millimetre wavelengths. "Herschel will detect objects that are too cold to emit visible light, and see through clouds of dust and gas that obscure new stars and planets from other telescopes," says Professor David Naylor from the University of Lethbridge, one of the Canadian scientists on the Herschel team. The space observatory should thus provide a wealth of discoveries during its planned three-year lifetime.

Herschel carries three instruments that analyze the light captured by the telescope:

• Heterodyne Instrument for the Far Infrared (HIFI)

• Photodetector Array Camera and Spectrometer (PACS)

• Spectral and Photometric Imaging Receiver (SPIRE).

HIFI is an ultra-precise spectrometer while PACS and SPIRE are cameras connected to spectrometers that can take photos of the sky in six different colours in the far infrared spectrum. These three instruments have different fields of view and cover different wavelengths.

These three instruments aboard the 3300-kg satellite are kept at a temperature close to absolute zero using liquid helium. It is important for the temperature of the instruments to be as cold as the surrounding environment in space so that the telescope can gather light from very distant stars and planets in the form of infrared radiation (or heat). To be able to maintain temperatures so low, the observatory must also be put into orbit far from Earth and away from any sources of heat. Herschel is therefore deployed about 1.5 million kilometres from Earth where it orbits around the second Lagrange point L2. It is also equipped with a sunshield that blocks radiation from the Sun, Earth and Moon.