Hi Tom, Your question is a harder to answer than you might think because it depends on factors that you haven't provided -- specifically, the angular resolution of whatever optical system you are using to image the Moon. When someone says something is a "point source", all they're really saying is that the object in question is below the resolving limit of the optics being used. Stars are point sources; satellites are almost always point sources. (There are the obvious exceptions of tethered satellites, and ISS through a telescope or high powered binoculars.) Planets are generally not point sources, which is why they "twinkle" far less than stars when low on the horizon. So when you compare a portion of the Moon to a satellite, you're comparing a resolved object with an unresolved one. The perceived difference in brightness then depends on your resolution. The worse your resolving power, the fewer "elements" (think pixels) the Moon gets divided into, and the brighter each individual element will be. For example, if you're comparing a sunlit ISS to a first quarter Moon with your unaided eyes, the brightness difference will be quite different than if you're looking through binoculars or a telescope. This is why the reversed binocular technique is used to estimate the Moon's visual magnitude -- the intent is to decrease the angular size so that it is closer to a point source, allowing comparison with stars or planets. --Rob ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www.satellite.eu.org/seesat/seesatindex.html
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