How do I choose the Observing constraints?
Most of the Observing Constraints must be specified by the user at Phase 1 and can not be changed at Phase 2. Since the execution conditions required by each programme are an important ingredient in the process of building up the Long Term Schedule of an observing semester, and thus determine which programmes can or cannot be scheduled, users are not allowed to specify at Phase 2 constraints that are more strict than those specified in the original proposal. Users can however relax the constraints during the submission of their Phase 2 material. The values in the OB constraint sets that are selected (and approved) during Phase 2 preparation (and review) cannot be changed later during the observing period.
The choice of the observing constraints is dictated by the nature of the observation: e.g. the observation of faint objects requires low sky brightness and, thus, dark time, while very bright objects might be observed also in grey or bright time. Compact and/or distant objects need very good seeing conditions to be resolved, while if such resolution is not desired, the observation is suited to more relaxed constraints.
Setting the Observing constraints, thus, requires a good understanding of the nature of the observations and of what the chosen instrument can or can not do. The user manual and the template manual of each instrument contain not only explanation but also good tips on how to use at best each instrument. Thus, if you have any doubt about what limit to choose for your Observing conditions, first look at the UM and, if still in doubt, ask for help.