Hi Steve: It's an interesting thought to use the moon's shadow at sunrise and sunset on the equinox to locate your east-west points. Although this can be done with the sun, you would have errors using the moon, unless there is an eclipse on the equinox also. If the moon is not in the same plane as the sun, it will not act like the sun.
Since the moon moves about two minutes/hour eastward in the sky, the only way you can do this with precision is to use precisely calculated times and lunar coordinates such as those sent to you by Jim Cobb. First you would find the meridian with the moon, using Jim's data, then find east/west. If there was a lunar eclipse on the equinox, then you would have to have a good unobstructed view of the east and west horizons which you probably have or else you wouldn't have asked the question. For fun, though, let's make the moon readings anyway to see what happens! We'll share our results after the event. Thanks for the luny question, John Carmichael >Hi all, > >It's only a few days to the equinox, which happens here in the middle of the >night (3:35 AST). I'm going to use the previous evening and following >morning to use a pole's shadow to make myself an East-West line, to compare >to my existing NS meridian line. I hope to find that they are at right >angles to each other. > >The moon becomes fully full just hours earlier, at 0:44 AST, so I'm >wondering if I can do the East-West thing by moonlight too. Is it a valid >thing to try? I've got a suspicion it only works when the equinox is also an >eclipse, so that all the bodies are all in the same plane. If that is so, >does the phase of the moon have any relevance, other than giving a strong >shadow? Unfortunately, my understanding isn't good enough to answer my own >questions. > >And are there any other special sundial-related phenomena which I should be >looking out for? > >Steve > >
