Stop me if you have heard this one before. A physicist goes into to a lecture hall to hear a talk by a famous astronomer on the nature of stars. Throughout the presentation the physicist gets increasingly angered as the astronomer makes one sweeping approximation after another. "Assume stars are perfectly round," says the astronomer. "Assume they are perfectly stationary. Assume they are perfectly composed of nothing but Hydrogen gas." All the assumptions are driving the physicist crazy. Finally the astronomer closes his lecture by saying, "And so you see, stars are really very simple." The physicist, pushed beyond his limits, stands up and yells back, "You would look simple too from a hundred light years away!"

OK, so it's not a very funny joke. It is, however, an old one among scientists and it illustrates a real aspect of studying astronomy, the closer you look at something the more complicated it gets.

Astronomy has always been a science that paints with a fairly broad brush. The relation between astronomy's theories and the answers it gets from observations is much looser than what one expects from other sciences, such as physics. In physics, if your theory states the answer should be 10 and an experiment gives an answer of 12 then you are usually very, very wrong. In astronomy 10 and 12 would be considered close enough to call the theory a success. Of course I am simplifying here quite a bit myself (I have not said anything about error bars) but the nature of studying Astronomy does affect the nature of what it considers "being right."

The reason astronomy can be less stringent about what constitutes being right is pretty simple, as that bad joke I started with illustrates. Everything studied in astronomy is so far away you can't get a really good look at. If your data (an image of a galactic center or some spectra of a distant quasar) is pretty "fuzzy" then it is hard to pull exact answers out of that data. Physicists don't have this problem. Unlike astronomers they don't make observations, they perform experiments. In an experiment what you are studying is sitting right there in your lab. You can, to some degree, control the situation and interrogate it to your hearts content. It is not that astronomers are less disciplined or exacting than physicists (well at least that is what astronomers like to think) but things are both harder and easier for them. What they are studying is often more messy than what physicists study (a star has more moving parts than a single atom) and the data they get just isn't up to providing very exacting answers.

Of course nothing stays the same and what is impossible to see yesterday may come into sharp focus tomorrow. Consider for example the case of Planetary Science and Space Physics. For hundreds of years astronomy really meant the study of the planets. In the age of Newton and Galileo, understanding the nature and motion of the heavenly wonders occupied the bulk of an astronomer's time. As telescopes became more powerful and people learned how to take spectra as a means of diagnosing celestial objects, stars became more included in the mix. Then something really amazing happened. Space probes took instruments off the telescope and put them right were the action was. We landed robots on Mars and sent cameras to Jupiter. Suddenly, for the solar system at least, what had been distant and fuzzy became close and sharply detailed. From that "moment" on, our solar system was no longer the domain purely of astronomers. The onslaught of information that came pouring out of solar system space probes changed the way people studied the solar system. When you can see the pock-marks on individual boulders you ask a different kind of question compared to the case when all you could make out were fuzzy patterns on an planet's face. If you want to study the solar system these days you are just as likely to end up in a department of space physics or planetary science as an astronomy department.

Planetary science, space physics and astronomy all use the scientific method, they all require that every hypothesis be testable based on how the real world really behaves. But advances in technology that improve the quality and quantity of data can lead to real changes in how a science goes about its business. When humanity learned how to send probes to the planets, planets grew past astronomy. Who knows, if we someday manage to travel to the stars then maybe Departments of Stellar Physics will be born and astronomy may only mean the study of distance galaxies. At that point, perhaps, the once distant stars will be appear really close and really complicated.

Visit these web links dealing with Space and Planetary Science.
http://www.lpi.usra.edu/lpi.html
http://www.lpi.usra.edu/library/website.html
http://www-ssc.igpp.ucla.edu/

Questions for Discussion

You are a detective working on a murder case. Think about the different ways you would carry out the investigation if the only evidence you had was:
1. A blurry photo of the killers face and a noisy recording of his or her voice.
2. A sample of the killers DNA and fibers from his or her car.