Night CAT

The night “Comisión de Asignación de Tiempos” (CAT) evaluates the observing proposals that guarantee to the Spanish community access to the majority of the night telescopes at the “Observatorios de Canarias” (OOCC): GTC, WHT, INT, TNG, NOT, Mercator, and Liverpool on La Palma, and Stella on Tenerife. Likewise, the CAT distributes the time allotted to Spain on the GTC, in the same way that it jointly manages, together with Mexico, the 2.5% of GTC time in collaboration with this international partner.

Telescope time is offered and allocated twice a year in periods of 6 months. Detailed information will be provided in the Call for Proposals. Allocation periods run differently depending on the telescope as indicated next: 

Semester Telescope Period

Semesters A

Due date: 1 Oct 2024, 21:59 UT  (2025A)

CAT meeting: end of November.


INT, Stella, TCS


NOT, TNG, Mercator


January – August*

February – July

March – August

April – September

May – October

Semesters B

Due date: 8 Apr 2024, 21:59 UT  (2024B)

CAT meeting: end of May.


INT, Stella, TCS


NOT, TNG, Mercator


July – February*

August – January

September – February

October – March

November – April

*A two month overlap period is adopted at the start and end of each period, when proposals from both semesters may be observed, in order to reduce problems with under-filled observation queues.

The night-time CAT is composed by three panels with five well-known astrophysicists each, one President (that represents the Director of the IAC), and one Vice-President.

There are different schemes to apply for observing time with GTC, WHT, INT, TNG, NOT, Mercator, Liverpool (LT), and Stella. They are all described in the menu on the left: Ordinary proposals (including regular and Large programs), DDT, Service Time, and various international agreements. See how to submit to learn how and when proposals  (of any category: regular, large, service, DDT, …) can be sent to the CAT.

  • The IAC80 is no longer offered through CAT since semester 2013A. Any interested potential users must directly contact the Head of Telescope Operations at the IAC [aoscoz at], or visit this web site.
  • TCS is now open to the CAT starting in semester 2024A.

 The night CAT can be contacted by e-mail to catiac [at], or by e-mail to its President.


Page updated: 3 Apr 2024.