Arecibo is an amazing, amazing telescope. It’s often easy to forget just how impressive it is, but I had the point driven home the other day, and I wanted to share. The sensitivity of a telescope is driven by the collecting area of the dish (or mirror, for optical telescopes) since a dish with a bigger collecting area can collect more photons from distant objects. Arecibo has a 300 meter diameter – it is the world’s largest telescope and hence is extremely sensitive.

I realized just how sensitive Arecibo is last week. I was working on a proposal to observe some sources from the ALFALFA survey with the Very Large Array (VLA) in New Mexico in order to see structure in these sources more clearly. (I talk here about how the VLA achieves better resolution of astronomical sources.) In order to write this proposal, I had to calculate how long we needed to observe my sources in order to have a good detection. These were all objects that were strong detections in the ALFALFA survey where they were observed for only 43 seconds in all (less than a minute!) by Arecibo. I calculated that in order to have a decent detection level with the VLA, it would take upwards of 10 hours of observation time. This strong difference comes from the vast difference in collection areas; the VLA only has twenty-seven 25 meter dishes while Arecibo is a 300 meter dish. I had always known that Arecibo is an awesome facility, but looking at this difference in time necessary to detect the same sources really impressed upon me what an amazing and unique facility Arecibo is.

43 seconds or 10 hours? I know which I’d choose.