Split-Night Policies


Support of split nights presents a distinct challenge to Observing Support. Normally Support Astronomers are available to help observers starting around 1 p.m. In order to properly support second-half observers they may be required to stay until 2 a.m. This long, 13 hour day is taxing on the SAs and prevents them from accomplishing more on other important Observatory work (e.g. Web page and infrastructure improvements). With some modest coordination of effort on the part of the split-night observing teams, we feel that this impact can be minimized.


When does the split occur?

Nominally the night is split at the midpoint between 12 twilights (which is almost the same as the midpoint between sunset and sunrise, 18 twilights, etc.). This time is displayed on the telescope schedule by holding your mouse over the date in the second column. A pop-up should show the sunset, midpoint, and sunrise times.

This implies that the first half observers should be done their final exposure at this time, and the second half observers and OAs should start switching to the new program and/or instrument, as appropriate.

Note that there are many reasons to argue for a switchover time either before or after the midpoint of the night: LGS-AO checkout takes time only at the start of the night; lost time tends to be at the start of the night; switching instruments includes overhead that might be shared between the groups; (the former two arguing for a switchover later than the midpoint, the latter arguing for one earlier). To keep it simple, we have chosen to simply use the midpoint for all instrument combinations.

Nonstandard switchover times

On occasion a TAC will award less than a half night to one observer and more than a half night to another, and pair them up. The TACs should let each observer know when the split is to occur. WMKO will not be responsible for arbitrating disputes over when the split should occur, although for both standard and nonstandard split times, observers are free to work out between themselves their own handover time. It is useful for observers to communicate such arrangements to their support staff, both OAs and SAs, so that the support staff can manage their time more effectively.

Protecting Your Data

The Keck Observatory Archive contains data from all instruments. This data is kept private for a certain proprietary period, nominally 18 months. (Observers can request extensions; see the KOA Web site for further details.) On nights with only one PI, assigning data to the correct PI and observing program is easy. On split nights, it can be harder. You can help protect your own data by setting the OBSERVER keyword when you are taking data. Ideally, include the PI's name in the keyword, even if the PI is not present. This will allow the automated ingest systems of the archive to properly associate your data with your observing program.

A GUI is being developed that will aid this, allowing the observer to change observer name, and possibly output directory (if the two observing teams are using different directories) with a single click.

Mahalo for your help,

Randy Campbell
Observing Support Manager