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Chris Benn
WHT manager

William Herschel Telescope


After the commissioning of WEAVE, i.e. from ~ spring 2020, 70% of the time on the telescope will be used to carry out dedicated surveys with the new instrument. The remaining 30% of the time is available to the community for observations with the current Cassegrain instruments, with visiting instruments or with WEAVE. Given the complexity of mounting and dismounting WEAVE, the current plan is to change to non-WEAVE instruments every ~ 9 - 12 months.

The current common-user instruments on the 4.2-m William Herschel Telescope are:

  • ISIS - single-slit spectroscopy, R < 10000, 4' slit, spectro-polarimetry
  • LIRIS - IR spectroscopy, R < 4000, and imaging (including imaging polarimetry), 4' field
  • ACAM - optical imaging, low-resolution spectroscopy, 8' field

Visiting instruments are mounted at the Cassegrain or Nasmyth (GRACE) f/11 foci or at the f/3 prime focus. The enclosure at the Nasmyth focus includes an optical bench. Recent visiting instruments include AOLI, CANARY, EXPO, FASTCAM, GHaFaS, HiPERCAM, PAUCam, PNS, SAURON and ULTRACAM.

The time-application procedure is documented here.

AF2, prime-focus imaging and NAOMI (AO) are no longer offered.

It takes less than a minute to switch incoming light between straight-through Cassegrain (usually ISIS or LIRIS) and folded-Cassegrain (ACAM) foci, and a few minutes to switch between Cassegrain and Nasmyth foci. Switching between Cassegrain and prime foci (which involves installing or removing the secondary mirror) is a daytime job.

Targets with significant proper motion (e.g. comets) can be observed with differential tracking.

The median seeing at the WHT is 0.8 arcsec during April - November. The dark-of-moon sky brightness at high ecliptic latitude is similar to that at other good dark sites, V ~ 21.9 mag arcsec2.

The CANARY laser guide star is in use at the WHT during a few nights per semester. During these nights, the risk of collisions with the pointing of other telescopes can be queried via the laser traffic control system pages.


2019 May 28: Update on the item below: due to a delay in delivery of part of WEAVE, ~ 3 months of 2019B is being returned to science, see the revised announcement of opportunity.

2019 February: In 2019B, the amount of time available for observing with the WHT will be very restricted, due to the upcoming assembly, integration and on-sky commissioning of the new MOS fibre spectrograph WEAVE from 2 September 2019 until spring 2020. The remaining 2019B nights, August 1 - September 1, will be used to finish off existing high-priority science programmes requiring the current instrumentation. Recent information about the timescale of the developments under way at the WHT (and INT) can be found on the ING instrumentation-update pages.

2017 March: The lower dome shutter has been repaired. Observations at elevation < 25 deg will no longer be vignetted by the dome (plot).

2017 February: AF2 and the prime-focus imager (16-arcmin field) will not be available in 2017B.

2017 January: Vignetting at low elevation: the WHT lower dome shutter is currently stuck in a raised position, and observations at elevation < 25 deg will be vignetted (plot).

2014 August: As a result of the ongoing rationalisation of instrumentation at the WHT, the adaptive-optics suite (NAOMI/INGRID, NAOMI/OASIS) will not be offered after 31 January 2015, i.e. from 2015A onwards.

2013 February: Differential tracking with autoguiding is now available, but is not compatible with some dither/nodding scripts (as often used with e.g. LIRIS). Observers interested in dithered, autoguided, observations of a moving target should contact ING.

For older/retired news items, click here.

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Contact:  (WHT Manager)
Last modified: 29 May 2019