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Re: Lunars question for Frank
From: Bill B
Date: 2005 Dec 9, 18:04 -0500
From: Bill B
Date: 2005 Dec 9, 18:04 -0500
> No. There is no "obvious" way to do this that is unambiguously correct. > Also, if phase is large enough to worry about, you can *see* it (once you > know > what you're looking for at least). As Venus gets closer to us, take a look at > it with your sextant's telescope. If it's approaching one arc-minute in > diameter, then through a 7x telescope, it will have an apparent diameter of > more > han five arc-minutes. That's plenty big enough to resolve with the human eye. > You'll actually see a tiny crescent through the sextant. So you should still > be able to estimate the location of the planet's center and park that spot > right on the lunar limb when you're shooting lunars. And by the way, when in > doubt about the size and phase, pull out a little telescope and take a look! Frank Thanks. Even with Alex's excellent binoculars I cannot see what he can, so would need a telescope. It strikes me that for practical purposes a combination of phase and apparent size would dictate use. At maximum elongation Venus would be half illuminated, but only 23" diameter, so offset from true center would be <0.6". Even if apparent elevations were equal, 0.1' would not be too much to worry about for most of us. Bill