The Herschel telescope is a classic Cassegrain design with a 3.5-m primary mirror — the largest ever launched into space — and a smaller secondary mirror. This powerful telescope allows astronomers to look deep into space by detecting light emitted in the far-infrared and sub-millimetre regions of the spectrum. Earth's atmosphere prevents most of this light from reaching ground-based telescopes. From orbit around the second Lagrange point of the Sun-Earth system, L2, 1.5 million kilometres from Earth, Herschel bridges the gap between previous infrared observatories and ground-based radio telescopes. This picture of the satellite was taken during testing at ESA’s European Space Research and Technology Centre, ESTEC, the Netherlands.