Doing Astronomy

Left, a picture of astronomy in action. The astronomer is comparing his calculation (with an old-fashioned analog computer) to the sky, thereby acting both as theorist and observer. Nowadays the computer would be digital and the observation would be electronic; in fact they might be carried out by entirely different people. The process, however, is the same.
A Roman seal-ring from the first century BC/AD. Image © the Syndics of the Fitzwilliam Museum, Cambridge; all rights reserved. Reproduction by permission.

Why?

Astronomy has had practical applications. I myself have used a sextant to navigate at sea, relying on computations of planetary motion performed by the U. S. Naval Observatory. With the advent of various satellite navigation systems (especially GPS), though, that sort of technique is pretty much obsolete.

One could make a case that astronomy has provided the motivation for many advances in science and technology. Geometry and trigonometry, for instance, were in part developed to calculate the size and shape of the universe, as well as the motions of the planets (under the Ptolemaic system). Newtonian mechanics, including the law of gravity, came about the better to explain celestial motions, and calculus was developed to calculate them. Quantum mechanics was necessary to understand stellar spectra, and nuclear physics to explain how stars shine. Special and general relativity find few applications on Earth, though they are routinely used in astronomical contexts. And so forth.

Too much should not be made of this. Astronomy has always been the occupation of a very small proportion of people, and the regular concern of not many more. It is not a way to get rich or famous. The overwhelming, and best, motivation to study astronomy is because you want to. You find it interesting, or inspiring. You are moved by the brilliance of the stars at night, or the beauty of a difficult equation which matches the data. The sudden insight which makes the pulsation of a star real to you, finally matching your theory to the tiny ripples of the microwave background, or possibly the first picture from a new infrared imager you've designed and built: these are reasons to do astronomy.

Who?

Not all astronomers are professional; in fact, amateur astronomers outnumber us, and contribute a great deal to the science. For instance, there are thousands of comparatively bright variable stars in the sky. Professionals are simply too few to monitor all of them, or even just those in which they specialize. So amateurs, on their own time and with their own equipment, watch these stars. Their efforts are coordinated by organizations like the American Association of Variable Star Observers, whose Web site is highly recommended.

Professional astronomers, nowadays, follow an identifiable career path. As undergraduates they may study physics or mathematics, or perhaps another of the related sciences, since there are few universities with an astronomy major at that level. Graduate school, almost always ending in an astronomy doctorate, is followed by one or more ``postdocs,'' temporary jobs (one to five years) nominally concentrating on research. Most of us are looking for some job security eventually, in the form of an academic job (some mixture of research and teaching) or something on the staff of an observatory (like CTIO) or a similar institution. Even though it remains the nominal goal of higher education in the subject, most people with a doctorate in astronomy do not end up with a full-time academic job in the discipline.

Astronomers are thin on the ground. With few in any one place, we tend to come from all over, and go to many places. We must be prepared to travel. When your postdoc in Wisconsin ends, there may not be anything opening up in your field in the same part of the country, or even the same country. I went from graduate school at Cambridge, England, to a teaching position at Annapolis, Maryland, to an observatory post at La Serena, Chile: three jobs, three countries, three continents.

Astronomy is international. One of my collaborators on a project is English; the other was born in Hong Kong and now works for the European Southern Observatory in Chile and Germany. A conversation I overheard in the cafeteria of one of the observatories started in English, moved into Spanish without a pause, then French, German, Spanish again, and ended in English. (If you're going to become an observer, Spanish is a particularly good language to learn.)

What?

Astronomers are famous for sorting things into classes. It's said that, faced with two objects, an astronomer will define three classes, I, II, and Ib, with the option of Ic and III depending on more observations. Astronomers divide themselves into theorists and observers, with some defining numerical simulation as a third class (I lump them with theorists), and others breaking out instrument-builders separately. (Some hold them to be, instead, a type of engineer. I don't entirely agree.) I started out as a theorist, but found myself unexpectedly with an observing program on my hands. Now I work about evenly on both sides. (I have not designed an instrument. Yet.)

Observers concentrate on collecting data at a telescope, then publishing it in some usable form for theorists to explain. The telescope may collect radio waves, gamma rays or visible light; observational techniques vary greatly, so an astronomer may be identified (for example) as a mid-infrared observer.

Looking through the eyepiece of a telescope is almost exclusively reserved for amateurs nowadays. Our data are collected in electronic images (using more refined, and much more expensive, versions of the detectors in digital cameras, kept cool using liquid nitrogen). So an astronomer will be found during an observing run in the well-lighted control room of a telescope building, kept well away from the telescope itself (human body heat would disturb the air, causing poor images), examining data on the screen of a computer terminal. (I like to go outside and look at the stars also.)

But observers cannot ignore theory altogether. In order to get time on a telescope, they must convince the time-assignment committee (TAC) that the project they have in mind will answer some important question in astronomy; big telescopes are too expensive to build and operate to allow someone to just look around to see what pops up.

For example: in our search for undiscovered Local Group dwarf galaxies, I went through available data systematically, coming up with a list of objects that might possibly be what we sought. I then calculated how big a telescope I would need, and what kind of observations to do, in order to check each one. Then I put together an observing proposal, explaining why it was important to find this kind of galaxy, and showing my calculations. I was awarded five nights on the CTIO 1.5m, to start off with. (I have submitted other observing proposals which did not get time. Telescopes normally get between two and five times as many observing proposals as they can handle. It's pretty competitive.)

Theorists, of course, differ in detail just like observers do. As a general summary, I can say that it is their task to find a (mathematical) model which fits the data. This could be by putting together a series of computer simulations with various assumptions, and choosing the one which best fits observations. Or one could find, as I did in a recent paper, that nothing seems to fit, so something must be missing. Sometimes everything works (well enough), and the result is a number: the age of the Universe, say.

Or perhaps a theorist runs his calculation, and finds that there have been no observations of the proper kind with which to compare his results. He passes this on to an observer, possibly by publishing a paper, alternatively by setting up a collaboration with him. Then suppose the observer finds that there is no combination of telescope and instrument which can possibly make the necessary observation. This information is passed to an instrumentalist (a clumsy word, but I can't think of a better at the moment), who comes up with a design to do it.

Of course, in real life, it's a much messier process, with thousands of papers published yearly on all aspects from basic theory to the performance of a particular detector, information and speculation flowing several ways, some of it mistaken, and now and then statistics miscalculated or misused. That only proves that astronomers are people.