Observing Constraints

During the observing night, the selection of targets to be observed depends on current conditions, especially seeing, sky transparency, sky brightness (Moon phase) and distance to the Moon. Night observing schedules will be adjusted accordingly, if weather changes. For each individual target they are set in the Phase 2, but the strictest ones must be well defined already in the Proposal.

In their proposals, the PIs should explicitly give the following information:

the maximum value of seeing, at which observation may be performed, in arcsec.
Sky transparency
the sky clearness and magnitude drop due to clouds, defined as a number between 0 (totally cloudy) and 1 (clear).
Moon phase/sky brightness
the acceptable brightness of the sky, coming from the illumination and elevation of the Moon - “dark” or “gray”. “Dark” is 0-3 days from the new moon or while the moon is set. “Gray” time is defined when the moon is over the horizon between 4-11 days. HSC runs are not allocated during bright time.
Moon distance
the minimum separation from the Moon, at which the target can be observed, in degrees. Only distances larger than 30 deg are allowed (to avoid significant contamination with stray light). For “dark” time, 30 deg is set by default, and cannot be changed by the PI. For “gray” time, it is the PI who sets the constraint.
Time constraints
window of time when the PI wants the observations to be performed. There are no particular limits for its length, and multiple windows are allowed. It is allowed to put several targets per window, or define several windows for one object. Note that the chance for the OBs to be observed becomes higher by specifying the time windows as relaxed as possible.

Observation constraints in the proposal (item 13 in the application form) should be the strictest value for each constraint : seeing (upper limit), transparency (T; lower limit), Moon phase (brightest allowable phase), and Moon distance (lower limit). For example, if one target requires seeing $\lesssim 0.8''$ while the others can be observed with seeing $\sim1.6''$, the PI needs to set the seeing constraint as $\lesssim 0.8''$ in item 13 of the ProMS.

Note that if an OB of a highly-ranked program is intended for restrictive conditions (for example seeing $\le 0.8''$) that are not currently met ($\sim1.0''$), this OB will not be executed at such moment, and a lower-ranked one that allows for given conditions ($\le 1.0''$) will be chosen. Relaxing the constraints increases the probability of performing observations. Defining different constraints for different targets is allowed.

In order to help choose the optimum observing constraints for a project, which will increase the probability of execution and still allow to accomplish the science goal, the PIs should familiarize themselves with the Statistical Information for Observing Condition Constraints in:


Starting from semester S17A, time-critical observations may be proposed. If the PI requires the targets to be observed at a specific time, please provide sufficient information, such as: date(s), time, and duration of the time windows. Use the Box 13 of the Application Form, or add comments in the target list (see Sec. 2.2). Note that the chance for the OBs to be executed may increase by specifying the time windows as relaxed as possible. If during the proposed time window the environmental conditions (seeing, transparency, etc.) are not met, the observations will not be carried out.