DDT proposals are accepted for every night allocated as Service Time on the NOT, TNG, and INT. For the WHT, DDT nights are scheduled exclusively as CAT DDT (see available nights). Full and half nights can be requested for DDT programs. These proposals can be submitted at any time once the scheduled dates are known and must be received 10 days (strict limit) before the observing date. DDT proposals can only be submitted through the online form. This period can only be reduced under exceptional circumstances.

DDT programs will always be executed in visitor mode. Programs using less than 4 hours must request Service Time. The Director will decide whether the proposal meets the requirements to receive the requested time.

Owing to the special nature of the observing time, the conditions for its use differ from those of normal CAT time. Some of the features of DDT on the WHT, INT, NOT, TNG, and Teide Observatory telescopes are listed below:

  • After the semestral CAT meeting, and once the normal observing time has been allocated, the nights reserved for CAT DDT and service-IAC will be made public.
  • CAT DDT time will generally be awarded on the most frequently used instruments of the telescopes concerned in order to better accommodate the observing calendar.
  • Any research group may apply for this kind of observing time.
  • Proposals may be presented at any time after the public announcement of the telescopes calendars for the semester. There is a strict limit for the submission of DDT proposals on the NOT, TNG and INT: 10 days before the required DDT observing night.
  • Proposals shall be submitted by means of a form (see instructions below).
  • Once the form has been received, the Director of the IAC shall make the appropriate contacts to ensure that the submission receives the necessary technical and scientific assessment as quickly as possible. The Director’s decision will be final and not subject to appeal.
  • The CAT DDT shall initially be programmed as service time, so that it will be used in this way in case no proposal receives a successful scientific and technical appraisal.
  • Any CAT service night on the INT, NOT, and TNG can be converted into DDT time (visitor mode) if requested and reasonably justified by the applicants These proposals must be submitted through this form.


  • Full and half-nights may be applied for CAT DDT.
  • As a general rule, proprietary period will be that of the applied telescopes.
  • Suitable proposals for CAT DDT include:
    • unforeseen or urgent transitory phenomena;
    • a topic of particular impact or importance needing urgent action;
    • those with a high element of risk, but also having high impact if successful;
    • follow-up of previous observations, where urgent action might lead to a result of high impact or be of a decisive nature;
    • to demonstrate the viability of a given program or type of observations;
    • high impact programs initiated by the Director of the IAC.
  • Unsuitable proposals for DDT-IAC include those that:
    • could be carried out during the next CAT semester with no significant loss of impact;
    • could have been comfortably accommodated within the previous CAT semester;
    • have been rejected by the CAT through its usual process of assessment, with no significant changes being made to the DDT-IAC proposal.
  • Inexperienced WHT and INT observers must be accompanied by an experienced observer. ‘Inexperienced’ here means unable, alone, to make efficient (and safe) use of the observing night, whether from general lack of observing experience, or from lack of experience with the specific techniques to be used. This lack of experience will not adequately be compensated by the start-of-run training provided by observatory support staff.
  • Any publications originating from this kind of observing time shall include a passage of acknowledgement along the following lines: “Based on observations made with the … telescope under Director’s Discretionary Time of Spain’s Instituto de Astrofísica de Canarias“.