Observing Policies

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The Green Bank Telescope is operated as a national visitor facility for qualified professional astronomers, including both expert and novice radio observers. General information on observing at the GBT and visiting Green Bank are described in the visitor information.

In addition to web documentation for self help (see the GBT Proposer’s Guide and the GBT Observer’s Guide), GBT Operations has a limited number of staff support astronomers who will aid observers in the setup and execution of their observations. In order to make most efficient use of the telescope and to conserve the time of our staff, we describe here the present practices and policies for GBT observing. Any changes and enhancements to policies, procedures, and observing facilities will be publicized through the Newsletter, our web pages, and through contact with the support staff.

General Information

OBSERVER RESPONSIBILITIES: As a general rule, the principal investigator has the responsibility for proper supervision of all aspects of the observing program. This means, for example, that each principal investigator is responsible for enabling all observing sessions, ensuring observers are available for observations, and obtaining all calibrations and other receiver/telescope parameters necessary for the reduction of his or her data. For this reason, we require that an observer be on site to conduct observations or a qualified remote observer be available.  In the case of student observers, the student’s adviser must accompany the student for at least the first observing run on the GBT.

REMOTE OBSERVING: The GBT supports remote observing provided the remote observer has been qualified for remote observing by the Head of GBT Science Operations. Most but not all of the required tools, procedures, and infrastructure are in place. Only those observers who have used the GBT before and have demonstrated that they are fully able to set up and observe on the GBT without staff assistance may observe remotely. Experience has shown that if an observer requires significant assistance, the process of providing this remotely is awkward to all involved, is an inefficient use of telescope time, and is overly time-consuming and taxing for our staff. Observers who are less experienced with the GBT are required to observe on site.

Observers who are sufficiently experienced and wish to observe remotely must contact the GBT Head of Science Operations (Toney Minter) at least two weeks in advance to request approval. The decision will be based on demonstrated experience of the observer and suitability of the program for remote execution. If permission for remote observing has been granted to a particular observer, it is required that he or she carry out the observations. The approved remote observer specifically must not pass off the responsibilities to an unapproved collaborator or student.

For approved remote observers, guidelines and suggestions for remote observing are posted online.

OBSERVER ASSISTANCE: Each observing program will be assigned a staff support astronomer (“friend”) to assist in the preparations for the observing run. You will be notified of who your support friend is when your project is approved for scheduling. The friend will serve as your contact person both before and after your run for all scientific and technical issues. Because of the support rotation scheme in use, a different scientist may be assisting you during your observations. This support scientist is generally available at the start of your run to assist in initial setup. This person or another scientist will be available as required during the course of the run, according to duty rotations. The friend or on-duty support scientist (or in his/her absence, the Telescope Operator) will coordinate contacting the technical or scientific staff whose assistance or expertise may be needed.

STUDENT OBSERVING: Many proposals have students who are either the P.I. or a CoI where the observations are conducted by students. To minimize the load of the GBT support staff, the first time that a student observes using the GBT, he/she must be accompanied by their supervisor (or an experienced GBT astronomer) and must carry out their first observations on site in Green Bank.

NON-STANDARD INSTRUMENTATION/SOFTWARE: Visitors who require special hardware or software configurations for their projects must make their requests at the time their proposal is submitted. Requests for non-standard facilities or capabilities will be considered in light of feasibility, priorities, project schedules, etc. Observers will be notified of the outcome when the results from the NRAO Time Allocation Committee are distributed. Last-minute requests for non-standard capabilities cannot be granted, in general.

PROPRIETY: Observers are scheduled on the telescope with the understanding that they will pursue only the program described in their observing request. Since we have many observers from various institutions working on related programs, we require that any observers wishing to change their program (e.g., source list, observing frequencies, etc.), or to exchange time with other observers, do so only with the consent of the Site Director and Head of Telescope Operations.


Regardless of whether observations are conducted on site or remotely, the observing will be most efficient if the observer and the support scientist work together to prepare for the run well in advance of the observations. Please make the following arrangements:

  • Contact your assigned staff astronomer before the start of the semester in which you may be scheduled. The program can be discussed, computer accounts and disk directories set up, and initial observing scripts created and reviewed. Having these scripts in place prior to the run will save much time in starting up the observing run.
  • If you plan on coming on site, arrive on site at least one business day in advance of your observations. This will allow observing plans to be reviewed and all last-minute preparations made. The staff astronomers can also give demos of the control and data reduction software which will save much time at the telescope.
  • Enable your project sessions as soon as you are prepared to observe to ensure the maximum possible opportunities are given to your project.

Telescope Scheduling

The GBT presently operates from ~300 MHz to ~100 GHz. Observations at frequencies above ~10 GHz are affected by atmospheric water vapor, and are best done in clear, cool, and dry weather conditions. Since Green Bank weather is highly variable, a dynamic scheduling system has been instituted.  This system is fully described on the GBT scheduling page.

Triggered Observations

Triggered proposals are for pre-planned observations of transients whose event times are unknown a priori.  Well defined triggering criteria are required. 

Triggered proposal for open skies observations must be submitted at the normal February 1 or August 1 proposal deadlines.  

Similar to fixed and windowed observations, triggered proposals should be ranked in the top quartile to be accepted with an A ranking.  Triggered proposals ranked below the top quartile would only be accepted as a result highly unusual circumstances and would receive a B or C ranking.

Once a trigger is activated, the following guidelines will be followed:

  1. A triggered observation will not be allowed to automatically override a sponsored time observation.  If the trigger has an A ranking and time permits, the GBT scheduler will attempt to negotiate with any sponsor to determine if the sponsored observation can be rescheduled in a reasonable and timely fashion to allow the triggered observation to occur.
  2. A triggered observation will not be allowed to override a fixed time observation (such as a VLBI observation or a pulsar Shapiro delay observation, etc.). 
  3. A triggered observation will only be allowed to occur under high frequency observing conditions if the trigger has an A ranking.  B or C ranked triggered observations will be limited to low frequency weather condition observing.
  4. Triggered observations can not automatically override a windowed observation’s default time.  For an A ranked triggered observation the GBT scheduler will work with the windowed observation’s proposal team to secure a new default observing time when possible. 
  5. A triggered observation will not be allowed to automattically override a maintenance period, a maintenance chance, shutdown periods, or any other time when telescope motion is not permitted (Thanksgiving and Christmas shutdowns, high winds, snow, etc.).  If the triggered observation has an A ranking, the GBT scheduler will work with the GBT Head Enigeer to determine if the observation can occur without interference to necessary maintenance activities if the observation can be scheduled on a maintenance day or a maintenace day chance.

Extra-Large Proposal Observing Blackout Policy

Extra-Large proposals are defined as any proposal requesting more than 1000 hours of observing time and typically running over multiple semesters.

Extra-Large proposals require a significant scheduling commitment for the Green Bank Observatory (GBO).  These proposals can strongly influence the ability to schedule other projects on the GBT.  In order to maintain a fair and balanced environment for all projects that are dynamically scheduled on the GBT, Extra-Large proposals must be able to observe any time they can be scheduled.  This means that while individual observers can take advantage of the blackout dates, Extra-Large proposals will not be allowed to blackout any time when observations can be scheduled.

The GBO is willing to work with projects to develop alternatives that may include operator run observing or service observing if the observing process is straightforward.

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