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    Re: Figure out LAN?
    From: Frank Reed
    Date: 2014 Sep 27, 11:04 -0700

    Sam wrote:
    "I usually calculate LAN from 12 UT and subtract the 1 hour for DST."

    Well, that sure won't work. If your purpose is just sight-planning, so that you don't waste too much time waiting for high noon or don't miss it by waiting a few minutes too long, then there are many ways to get the time of noon. One of the easiest is to take the average of the sunrise and sunset times for your location which you can find in numerous apps, online sources, tv weather, and even newspapers (just make sure the source is for a location with nearly the same longitude as you). All you do is split the difference. Near the equinoxes, there's a small difference between this average and the time of noon, but it's nothing to worry about in practical terms. Another way to get the time of high noon (local apparent noon) is to use some sky simulation software like Stellarium (if you don't have it installed or haven't learned how to use it --or similar-- you really should do so). Then all you have to do is advance the Sun across the sky using the time controls in the software until its azimuth is exactly 180°. That's high noon. Another advantage of such software is that you can experiment and see just how much the altitude changes with time. Does it really matter if you're 30 seconds late observing the Sun at LAN? How about one minute late? When does it actually become an issue given your own accuracy expectations?



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