Learning from an observation
What we see depends on what we’re looking for.
Our astronomer has almost completed his evaluation of planets passing in front of other planets, one result of which we noted last week, and his conclusion is not too surprising. An expert naked-eye astronomer, knowing what to look for and when, could in some cases have seen some effect. But of course an ancient astronomer would not have known either of those: he had neither the idea of a planet as a small disk, nor a prediction accurate enough to say when one would pass in front of another. If “chance favors the prepared mind,” as Pasteur said, his mind would not have been prepared.
But we note that the mind can be too prepared. The ancient philosopher-physicists, epitomized by Aristotle, concluded that the heavens (the Moon and everything above it) must be eternal, unchanging, and therefore only moving in perfect circles. Any sign of change must be either illusion or confined to the lower regions closer to the Earth. Thus comets and meteors are (in our terms) phenomena of our atmosphere, and not the proper subjects for astronomical observation. In particular, changes in stars are ruled out.
This was not a universal conviction. Indeed, throughout the ancient and medieval world there was a tension between the physicists (upholding the principles) and the astronomers (trying to match the observations). The latter, trying to “save the phenomena,” indulged in not-quite-perfect circles, and in particular Ptolemy and Hipparchos recorded observations in case stars appeared or disappeared, or changed their place slightly. Still, a medieval observer would certainly have dismissed as erroneous any obvious violation of physics as he understood it.
The idea of “saving the phenomena” as a test of the validity of the physics was perhaps the greatest advance of the Scientific Revolution. Among other things, it allowed much greater freedom for observers to record what they (thought they) actually saw.
Our astronomer enjoys leafing through records of nineteenth-century observations. The observers were sufficiently scientific to set down everything, and did not yet know enough of stellar structure and evolution to edit their conclusions. Hence we find many very steady stars suspected of variability, and others that might be shining by reflected light. There is a freedom of speculation that, one might say, is missing nowadays. Indeed, the nagging question appears: what may we be ignoring in observations now, because we know what has to happen?
Reviewing the current literature, we (cautiously) suggest that it’s not a great danger. Indeed, there seems to be more of an opposite tendency. Data of borderline significance are often published, because they might show something important, if true. And mostly they are not. We’re not sure that the “over-prepared mind” has been banished, but it doesn’t appear to be the main danger to science nowadays.
