As I write this, we are just getting on-sky with the Green Bank Telescope to do some neutral hydrogen (HI) observations. We are remotely observing and David is at the controls getting things going. The first step is to focus the telescope (easy to do at L-band!), determine pointing offsets (difference between where the telescope thinks it’s pointing, and where it actually is pointing), and balance the IF rack (ensure the system responds linearly to incoming signal). This first portion takes about 10 minutes or so. Once that is done, we will move to a strong calibrator source, generally a radio loud quasar or a radio galaxy which is unresolved by the GBT. We will do quick observations of a calibrator so we can later calibrate our data to accurate measurements.

Once the setup and calibration is completed, we will move to our source and begin taking data. This evening’s observations are part of a modest survey to look for HI in compact groups of galaxies. They are an interesting selection of objects, much smaller than large galaxy clusters or groups. There is a mix of elliptical galaxies and spiral galaxies, although elliptical galaxies seem to be more prevalent. We only have a 1.5 hour observing block tonight, so with calibrations and overhead (slewing the telescope, etc), we will only be observing a single compact group. We have already observed a number of groups, and will observe more during future runs, including one tomorrow and one on Wednesday.

But, soon it’s off to the calibrator!