Apollo 11

Pete Mao (Caltech) sent me a note for Newton's birthday, pointing out that all sensible transfer orbits to and from the Moon ought to have half-periods (transfer times) of about 5 days. And yet, as he also pointed out, Apollo 11 came back in 2.5 days. What gives? Did NASA waste fuel to improve the filmic value of the mission, or does the enormous tidal effect of the Sun change the sensible set of transfer orbits for some reason I don't understand?

(His note on this subject also had a nice discussion about what a 5-year-old wants when he or she asks a scientific question, and why just answering it is the wrong response.)



I posted about diagnosis on my research blog and that made me realize that I should post here too. Almost all of science is diagnosis: You must diagnose your code, you must diagnose disagreements between theory and observation, you must diagnose inconsistencies in results. And yet diagnosis is so far outside any formal curriculum, no-one knows what you would even think about teaching there! It is taught to doctors and automobile mechanics, but not astronomers, who need it just as much, or perhaps even more.

Seymour Papert makes this point very clearly—and much more generally—in his book Mindstorms. One of his main arguments that computers must play an important role in education, or in thinking about thinking, is that programming a computer forces us to confront bugs. These require diagnosis (and also lead to interesting insights, a consequence he discusses extensively).


astronomical detectors

Another problem-set problem, inspired by an email today:

Imagine measuring the brightness of two stars, one of which is a 100,000 K blackbody, and one of which is a 3,000 K blackbody. You are interested in the flux ratio in the V band. In one experiment, you perform this pair of measurements with a (flatfielded, calibrated, etc) CCD with a standard V-band filter on it. In another, you perform this pair of measurements with a bolometer with the same filter on it. Do you expect the flux ratio you measure to be the same in the two cases, and, if not, what is the expected difference? Imagine that both detectors are very high in quantum efficiency over the wavelength range of interest, and that you are capable of making accurate, calibrated, sky-subtracted measurements in both cases.



Future problem-set problem: These two images were taken from the same three-space camera position, with the same digital camera. What, physically, was changed about the camera, and why did it have the effect that it did?