The Herschel Space Observatory was a space observatory built and operated by the European Space Agency (ESA). It was active from 2009 to 2013, and was the largest infrared telescope ever launched until the launch of the James Webb Space Telescope in 2021. Herschel carries a 3.5-metre (11.5 ft) mirror and instruments sensitive to the far infrared and submillimetre wavebands (55–672 μm). Herschel was the fourth and final cornerstone mission in the Horizon 2000 programme, following SOHO, Cluster II, XMM-Newton and Rosetta.