Astronomical tomography:
An orbiting telescope, the Hubble, made, placed and maintained at considerable expense, has produced some pleasing pictures and done some good science. Advantages of being in orbit include the absence of air turbulence and glare from nearby cities scattering back into the instrument. One can try to get away from cities, but on the surface of the earth the air is a given.
I once heard that the Chinese were building a telescope in Antarctica to be placed atop a 100 foot tower. The expectation was that this would put it above 90% of the problems caused by turbulent air. Antarctica is not very convenient and is in fact farther away from China than the Hubble is from the earth, but it still has to be cheaper working in Antarctica than in space.
Years ago, before the world became digital there was a technique in x-ray studies called tomography. The point of an x-ray study is to be able to look through something to see something behind it, like to see a broken bone beneath skin and muscle. The technique was to move the film and the x-ray tube in such a fashion that one zone within the patient remained stationary on the film while things close to the film and farther from the film were blurred so that they effectively vanished. Similarly there is an old technique that used to be used with cameras. You could take a picture of a crowded street with pedestrians and traffic and by making the exposure long enough you could make all the cars and people disappear from the final picture.
In my heedless youth I would sometimes take long trips by motorcycle. Since I was too cheap to pay for a motel I would just drive through the night, which meant getting more experience than was prudent at driving in darkness and fog. I would spend what seemed like hours staring into a featureless white scene peering intently for any sign of tail lights, which would mean I was overtaking somebody, which didn’t happen often. What did happen rather regularly was the fog would begin to brighten and I would see two shadows of myself and my motorcycle cast in front from headlights behind me. The shadows would drift farther from each other as the car caught up with me. That was my signal to accelerate until the shadows were only diverging very slowly so the car’s relative velocity to mine was very low. That gave the driver the best chance of seeing me. I would know he was going around when both shadows moved abruptly aside. Then I would slow to make it easy for him to clear me. I would try then to keep up, but I found I was outrun on a regular basis. The fact that I am alive is a tribute to the reflexes of many strangers in those long lost times.
Two observations stuck me that made no sense. One was that the drivers of the cars obviously were seeing a lot more clearly than I was. They could successfully travel at speeds I could not manage even though my motorcycle was easily capable. The second observation was that although the way forward was invisible, the side of the road was always very easy to see. I simply decided that the glare from the headlight was causing the invisibility, but that wasn’t really a satisfying explanation.
Jump forward more years than I like to think about and here I am doing my research project on the fruit flies. The daily count of the flies amounts to the hard data. But now for years I have also tried to count when the first little maggots creep up the sides of the bottles. That count has never proven to be valuable but I keep it up in case something remarkable changes.
Of course the windows through which the census of adult flies is taken are kept fairly clean, but the maggot count window is rather neglected. There are lots of fly specs, and it is through these fly specs that I must read the date when the particular bottle was placed. After some years I began to move the bottle around to find a clearer spot to read through. And now after several years I notice that it works, but not because there is a clear area. It works because the bottle is moving. As with a tomogram the flies blur away as the eye follow the label.
That might be why the car drivers see so much better; the individual droplets of mist are too far away to see clearly, but they are much closer to the eyes looking through goggles. Similarly the side of the road is quite clear; the droplets are speeding past far too fast to be seen. I am not disposed to rent a motorcycle and go out some foggy night to do the obvious experiment; besides it would be illegal. You can’t turn off your motorcycle headlights these days. But if you could, and if you put a lamp on your head you could make two observations. When you are stopped things look equally clear in all directions. When you are moving the direction you are moving is the direction of greatest obscurity. Don’t do it. If you have read this far you are a frequent and alert reader of my web site and you are far too valuable to the world to risk your life on such a caper.
But think about a telescope and air turbulence. My first assumption would be that turbulence, like traffic, is random and cancels itself out. But perhaps not. Perhaps there are shifting but characteristic patterns that degrade the view. If so you could put the telescope on a track, something like a very smooth running merry-go-round and gear it to stay fixed with respect to the stars. If it helped it would be a very cheap way to improve the view.
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