NavList:

Brad, you wrote:
"I believe we can perceive about a 4' change in angle, so 4" is out of the question for the naked mark one eyeball."

It's hard to say what would qualify as the smallest "perceptible" change in angular size. The limiting resolution of the unaided eye is about 1 minute of arc (a little better under ideal conditions). But noticing a change in size is a very different task. If we could view the perigee Moon side-by-side with the apogee Moon, the difference would be small but plainly visible. The small variations in perigee from one month to the next would almost certainly not be visible even in a side-by-side comparison. You can experiment with a scale model. Hold a common pencil at arm's length. The eraser on an ordinary pencil at arm's length is just about the right size to match the Moon. Now hold another pencil three inches closer to your eye in the other hand. That's the difference from perigee to apogee to scale. If you bring your hands together so that the scale moons (pencil erasers) are next to each other, there is a small but noticeable difference in apparent size. If you separate them by anything more than maybe twenty degrees, there's no comparison and they look the same.

You suggested:
"If you're really good, I suppose you could measure it with a high magnification scope. I may just try."

Yes. You could measure it with a sextant. It's a lunar, where the other body just happens to be the SAME body. A limb-to-limb measurement of the Moon's diameter has many of the observational properties of a lunar distance. It's easier since it's a very short angle. You should be able to measure the Moon's actual diameter to an accuracy of about 0.1' of arc by averaging a handful of observations. As always, the IC is everything here. If you don't have that pinned down to a tenth of a minute of arc, your measurement can't be better than that. It would be fun to try to measure the diameter (pole to pole, btw!) for several days around perigee. You should be able to detect the maximum diameter easily.

-FER
PS: You said you thought you saw the story on a CNET feed. Yes, they did have an early article on it so that makes sense. By the way, in case you follow their science stories regularly, the guy from Massachusetts almost certainly did NOT find a piece of the Mir space station on the banks of the Merrimack River! :)

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