Observatory 1: Green Bank, part 2

Radio astronomy is a fascinating branch of science, in part because it is in some ways very different from optical astronomy. Since we can’t see radio, you can observe and gather your data anytime, day or night. The dishes that act as telescopes get basically one-pixel resolution. So where your phone or camera has several megapixels resolution, the largest radio dishes basically act as a single point, if I understand correctly. It is by panning the dish across an object that you are able to form a picture from it. But there is also a great deal to be learned from radio data without even making it into a picture. For example, different chemical elements give off unique radio frequency signatures. Hydrogen emits radio at 21 cm wavelength, which translates to a frequency of 1420.4 MHz. Since hydrogen is the most abundant element in the galaxy and the universe, you might think that trying to map it would be a little crazy. But an interesting thing happens when you observe a span around that 1420.4 MHz. Because of the nature of space and time and electromagnetic waves, we can detect if the hydrogen being observed is moving toward us or away from us, and how fast it is coming or going, and how far away it is from us. That’s a lot of information! So mapping the hydrogen in the galaxy is like making a navigational map of rivers, harbors, lakes, and seas. It gives you an idea in 3-D of how the galaxy is built and how it is moving and changing.

At the Green Bank Star Quest, I got to do some of that kind of science directly! After a workshop on the basics of radio astronomy (where I learned some of the above), we were given the opportunity to use the 20-meter dish to look at … anything we wanted! A couple others in the class and I looked at two significant radio sources, Cass-A (supernova remnant) and Orion-A (star-forming region). Later we added the Owl Nebula, the moon, Mercury, and a variety of other objects. Some were strong radio sources and others less so, and Mercury not at all, which is weird. I still have a lot to learn about what our scans mean, but it was amazing to be able to run a world-class instrument.

I also got to use the 40-foot radio dish at GBO. It is, I think, the smallest of the active dishes at GBO, but let me tell you, 40 feet is not a small dish! About seven of me end to end would fit across it. This dish is also rather historic in that, as I am led to understand, it was used by Frank Drake for the first SETI (search for extraterrestrial intelligence) experiments in the 1950s and 60s, Project Ozma. This is a transit dish, which means it is always pointed along the N-S meridian, rotating up and down but not side to side. There is a control room in a below ground bunker that looks like a science office from the 1960s. A couple stacks of electronic equipment stand in one corner, the instruments appearing to be of 1980s vintage. By means of analog dials and switches and a digital frequency selector and a tractor-feed data record with two pens, one can collect actual science data by aiming the telescope, selecting a frequency range, and interpreting the graph on the paper strip. It is wildly old school science, and it was a blast! Three of us worked together to get some data under the tutelage of our guide Sophie, but I got to take home the data. I followed some directions on a hand-out and found that the blob of hydrogen we investigated near the center of the galaxy was moving away from earth at (if I recall correctly, as I don’t have it here with me) 48 km/sec. How cool is that?

Along with experiences in several other lectures and workshops, I found that I was just having the best time being a science student again. It gave me a thrill, not only to be learning from professional scientists, but also to do actual science. To be transparent, I also got a thrill from being a good student, knowing or figuring answers to questions ahead of others in the class. Yes, I like being an overachieving, curve-busting, teacher’s pet and always have.

But really, it’s the thrill of the science.

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