Here’s a blog post from Martha about some recent observing time we lucked into. Enjoy!
Although the majority of the observing time at Arecibo goes to passive radio astronomy, observers also make use of its powerful transmitters to do radar astronomy (remote sensing of the Moon, planets and their satellites and rings) and atmospheric science, especially incoherent scatter radar to study the Earth’s ionosphere. The atmospheric sciences experiments are organized as large campaigns (“World Day’s”) making use of simultaneous experiments using a “chain of radars”, one of which is Arecibo and conducted over a week or so. But they depend on the use of the transmitter, and once in a while, the transmitter fails and cannot be fixed in the short run. If towards the end of an ionosphere campaign, there is a hardware breakdown and it is clear that it cannot be fixed, the telescope schedule is quickly reassigned to other programs (so that the telescope does not go unused). The ALFALFA observing program (A2010) is one of those that is “on call”, ready to fill in on short notice.
So, on Dec 14th, we were notified that we could observe on two nights rather unexpectedly. Since we were notified late in the day and it was during the week of final exams for many students and also snowing (which complicates travel and parking; fortunately MH and RG have vehicles which drive well in the snow), Martha decided the best thing to do was to run the observing herself.
The first issue was “What should we observe”? The time allocation was also for the “spring block”, 07h30 < R.A. < 16h30, and we had not really been expecting to observe before January. Scheduling a many-year survey in an optimally-efficient manner is not always as easy as one might think. Since we only observe at night (the Sun is a strong radio source which moves through the sky and therefore interferes with our "minimum intrusion" observing technique), the time we were assigned covered only 07h30 < R.A. < 11h50; we will have to observe the rest of the block later. Martha also realized that since AUDS (program A2133, another large scale survey using Arecibo) was not scheduled before (as is normally the case), it would be an ideal night to observe south of zenith. The AUDS target is north of zenith, so if we follow them, the telescope has to be slewed all the way around to the other half of the sky. Because of her quick thinking, we got in two south of zenith runs, almost completing what we need south of the zenith strip.
It is rumored that the atmospheric scientists think of us as "telescope vultures", circling nearby, hoping that their experiment fails. But, that is not really true, though indeed, their disaster becomes our opportunity. We point out that on occasion there is reciprocity: if a target-of-opportunity (like a potential Earth-impacting asteroid) needs immediate observing time, then our allocated runs can be (and have been on occasion) preempted at the last minute. The main point is that telescope time is a precious resource, best used to maximum efficiency, which sometimes requires last-minute changes to the schedule.