William Herschel Telescope

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. In 2023, WHT was dedicated to WEAVE's commissioning. As of 9/2025, WEAVE commissioning continues, with normal WEAVE surveying expected to begin before the end of the year. Possibly some science has been carried out during WEAVE test runs. WHT instruments listed before installation of WEAVE:

• ACAM - Auxiliary-port Camera - optical imager/spectrograph.
• A&G Unit - Cassegrain Acquisition and Guidance Unit.
• GHRIL - Ground-based High Resolution Laboratory.
• GRACE - Ground based Adaptive optics Controlled Environment.
• ISIS - Intermediate dispersion Spectrograph and Imaging System.
• LIRIS - Long-slit Intermediate Resolution Infrared Spectrograph.
• PF-QHY - Prime Focus (WEAVE optics) sCMOS camera.

Some of the above may be available for science when WEAVE maintenance allows for such use. Some of WHT's earlier-listed (past) instruments:

• AF2 - robot fibre positioner.
• GLAS - Ground-layer Laser Adaptive-optics System.
• INGRID - Isaac Newton Group Red Imaging Device.
• INTEGRAL - integral field unit.
• NAOMI - Natural-guide-star Adaptive Optics for Multi-purpose Instrumentation.
• OSCA - Optimised Stellar Coronagraph for Adaptive Optics.
• OASIS - Optically Adaptive System for Imaging spectroscopy.
• PFIP - Prime Focus Imaging Platform.
• SAURON - Spectrographic Areal Unit for Research on Optical nebulae.
• WYFFOS - Wide Field Fibre Fed Optical Spectrograph.

Another Herschel is the Herschel Space Observatory.