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The William Herschel Telescope (or WHT or Herschel Telescope) is a 4.2-meter monolithic-mirror optical/near-infrared reflector telescope in the Canary Islands, operated by the Isaac Newton Group of Telescopes (ING). It came into service in 1987 as the world's fourth largest telescope and was early among modern large telescopes to use an altazimuth mount. WHT has now been dedicated to the multi-object spectrograph, WEAVE (for WHT Enhanced Area Velocity Explorer), which it will use whenever the instrument is operational, much of that time for WEAVE-based surveys. WEAVE commissioning took precedence in 2023, with some science operation beginning in October 2023. Some WEAVE functions (additional modes of operation) are expected to enter science operations in late 2026 or early 2027. These older WHT instruments are now available only when WEAVE is offline for maintenance:
Other WHT instruments listed before WEAVE's commissioning:
Some of WHT's earlier-listed (past) instruments:
Another Herschel is the Herschel Space Observatory.