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    Re: An exotic lunar distance puzzle
    From: Frank Reed
    Date: 2011 May 3, 16:27 -0700

    You will not be able to come up with a really definitive value for dip because that beautiful sharp horizon you see in the photo is probably the top of a high altitude cloud deck. What would the dip be under various assumptions? Suppose that cloud deck is six miles above sea level (in thin air). Then you would have to measure height from that altitude. Also, what was the actual altitude of the space station? The number I gave previously is really an average altitude. At heavens-above.com, there's a nice graph that shows station altitude over time, but it doesn't go back far enough for this photo. We could dig it up, but given other inevitable inaccuracies in the analysis, it might not be worth the effort.

    By the way, don't bother with an exact value for the Jupiter-Moon angle since they frequently use lenses up there that have a significant "fisheye" effect. Long anglesare suspect. There are lots of fifth and sixth magnitude stars right near the horizon. Have you identified the star just above the Moon? I think that's our best bet for a lunar distance here. That star appears to be almost exactly one lunar diameter away from the dark limb of the Moon. You won't be able to use common lunar distance analysis software for the analysis, but you don't have to. You can do it "backwards". Just play with the time and location in your favorite astronomy software until the "topocentric" view looks exactly like the image.

    And just to remind you from a post I made late last year, NASA astronauts actually shot real lunar distance sights using handheld sextants in one of the "make-work" experiments aboard the Skylab space station in 1973. When the experiment was planned, folks at NASA with stars in their eyes were thinking about a manned Venus flyby mission, and they were trying to develop a true manual navigation system. The Venus flyby and all such expensive manned missions were cancelled years before Skylab was launched. In some ways, Skylab WAS that interplanetary spacecraft, marooned in Earth orbit.


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