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Technical information




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For ING Staff (internal)

Cecilia Fariña
INT Telescope Manager

Isaac Newton Telescope

The Isaac Newton Telescope (INT) has a 2.54-m diameter primary mirror. It uses a polar-disc/fork type of equatorial mount. Instruments can be mounted either at Cassegrain or Prime focus, offering the possibility to carry out both intermediate-low dispersion spectroscopy and wide-field imaging.

INT Instruments

The instruments offered at the INT are:

  • Wide Field Camera (WFC): Imaging over a 33-arcmin field with a wide variety of broad- and narrow-band filters.

  • Intermediate Dispersion Spectrograph (IDS): Medium-low resolution long-slit spectroscopy. IDS is offered with a set of 16 gratings providing dispersions in the range of 4-0.24 Å pixel-1. It can be used with Red+2 detector (default) or EEV10 detector (if requested and justified in the proposal).

Detailed descriptions to operate the telescope and instruments can be found the in the instruments web pages and links therein.

Changing from WFC to IDS and vice-versa requires daytime engineering work. When WFC (mounted at Prime focus) or IDS (mounted at Cassegrain focus) are in use no other instrument option is available.

Information to apply for observing time can be found at Applying for Telescope Time.

For preparing and planning observations, read the information at Planning Observations.

Observing at the INT

Visiting observers

Visiting observers at INT should have considerable end-to-end observing experience with medium-sized telescopes and be familiarized with the instrument, telescope and health and safety documentation prior to the starting of the observing run. As there is no Telescope Operator (TO) at the INT, observers are responsible for all aspects of telescope and instrument operation during the night. A detailed introduction to the telescope and instrument is given by the INT Support Astronomers (SA), who will contact the PI in advance, to confirm the instrument configuration, discuss the observing plan, etc. The SA will be at the telescope from the afternoon until about midnight of the first day of the run and will be reachable at ORM Residencia during the whole first night of the run. Observers with little (or long ago) experience at INT are encouraged to spend the previous night to the start of their run at the telescope. Please contact your INT SA to coordinate this.

Service mode observations for regular INT programmes

PIs of regular proposals at INT now have the possibility to request service observations for their IDS or WFC programmes in the new scheme of INT Service-mode observations.


  • Please read through the Emergency Procedures for Visiting Astroomers, and if you have any doubt about it ask your INT SA.

  • Please read carefully the information about filling the WFC or IDS cryostat.

  • In WINTER time, before arriving to the telescope, read the recommendations and advices about Ice Safety.

  • When the laser is working at the WHT (e.g. by CANARY), the INT observers should monitor the "TELESCOPE SUMMARY" in the Laser Traffic Control System web page, to check if there is any limitation in the INT pointing due to possible collisions with the laser.

  • For any question do not hesitate to contact your INT SA, Instrument Specialist or INT Manager.

Other information

  • When the dome lower shutter is down the lower observation limit is to Elevation=33 deg. When the dome lower shutter is raised the observation limits are between Elevation=20 to 34 degrees (outside those limits the lower shutter stars to vignette).
  • The INT median seeing is about 1.2 arcsec (see INT seeing and image quality internal report). More information on local seeing can be found at the ING seeing measurements web pages.
  • Check the Site Quality page for information about extinction, sky brightness, weather conditions, etc at ORM.
  • The INT weather downtime is about 20-25% per year.
  • The INT technical downtime is around 2% per year.
  • Information about accessible sky area to INT at INT Pointing Limits.

INT looking ahead

ING is finalising an agreement with the Cambridge-led THE Consortium for the deployment at the INT of HARPS3, a high-resolution stabilised spectrograph which will conduct a 10-year survey aimed at discovering Earth-mass planets in Earth-like orbits around the nearest G and K-type dwarf stars. The THE Consortium will carry out a full upgrade of the INT to allow for remote or robotic operation. The 50% of the INT time will be devoted to the THE survey, the remainder being available as open time to be allocated by the TACs. For more information please check the ING page about Changes to the Availability of Instruments 2017-2019.

INT Brief History

The INT saw first light in 1967 in Herstmonceux, United Kingdom, the site of the Royal Greenwich Observatory. At the time, the INT was the 5th largest telescope in the world (acc. to wikipedia). Aiming at a site with better weather and sky observing conditions the INT was moved to the Roque de Los Muchachos Observatory (ORM) and resumed operations in 1984, as part of the Isaac Newton Group (ING). More information about the INT can be found on the public information web pages.

Front picture: "Moonlight", from

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Contact:  (INT Telescope Manager)
Last modified: 22 May 2017