> Also, since light pollution is such a problem near cities, I wonder if that > pollution is mostly around a particular wavelength. If so, would it be > possible to make a filter to look through that would not pass a particular > range of wavelengths? I'm no physics expert, but something like this might > be possible to improve the visibility of objects the sky near large cities. yes, it's possible to filter out some wavelengths of light pollution. problem is that there are a lot of different wavelengths to filter out, depending on what kind of light pollution. High-pressure sodium, low-pressure sodium, mercury-vapor, household incandescent, and all the varieties of 'neon' each give off their own range of wavelengths. So if you're near high-pressure sodium highway lights, you'll have a different problem than if it's your neighbor's million-watt bug zapper. there was a really good article in Astronomy magazine about the subject, quite a few years back (like 10 years ago, when I was still reading it). try looking it up in the library. Carl Soderstrom -- Network Engineer Real-Time Enterprises (952) 943-8700