Determining Az/El (was: Re: Gorizont 14 back again)

From: Markus Mehring (m.m@gmx.de)
Date: Wed Aug 29 2001 - 12:15:26 PDT

  • Next message: Matson, Robert: "Determining az/el"

    On Wed, 29 Aug 2001 00:03:31 +0530, you ("Ulhas Deshpande"
    <dulhas@im.eth.net>) wrote:
    
    >Question: How do I go to AZ and Elev data from what the heavens above page
    >shows?
    
    Okay, this may make for a boring read for anyone with just a bit of
    experience, but some newbies might appreciate it.
    
    The azimuth value gives you the direction, like cardinal points on a
    compass, clockwise. 90 is East, 180 is South, 270 is West, and 0
    (=360) is North. To determine the direction, you need to know where
    (geographically) north is for your location. Looking for Polaris is always
    a good idea on the northern hemisphere, since it sits almost exactly north
    (they don't call it Northern Star for nothing... :). Note that Polaris is
    significant because of its prominent location, not because of its
    brightness. It is a frequent misconception that Polaris might be the
    "brightest star" or something, which it of course is not, it is actually
    somewhat faint.
    
    The elevation tells you how high the object is in the sky. 0 is your
    horizon, 90 your zenith, exactly straight up. Negative values are below
    your horizon (the opposite of the zenith at -90 is called "nadir", BTW).
    Of course there can be no elevation value beyond 90 or -90.
    
    Knowing this, a pair like Az 90 and El 45 tells you to look exactly east
    and halfway up. :)
    
    It generally helps during observations to know your sky, know which stars
    and constellations are where at what time. It also helps if you pick
    yourself landmarks for a specific spot where you're standing, like a
    rooftop or a tree that you know is exactly west when you're situated in
    exactly that corner of your backyard, something like that.
    If you know one direction, you can easily determine the others, of course.
    I'm using a bit of a trick for the more "odd" directions if I need to get
    it done quickly: if you set one foot into one direction, let's say your
    left foot to north, and then set the other foot exactly in a 90 angle to
    it, heel to heel (!), you not only know where east is, but your body will
    also swing exactly in between and you'll automatically end up looking to
    the NE at Az 45. From there you can step-and-swing into other directions
    (such as leaving the right foot at 90 and turning your left foot to the
    known 45, your body tension will let your end up looking into Az 67.5,
    a.s.o. a.s.f.). This is not a very accurate method, but it can be quite
    helpful at times.
    
    A similar yet more "guessing" method works for determining the elevation.
    It is surprisingly easy to point your hand, arm, binoculars or what else
    you have to an elevation of 45, because (surprise surprise...) that's
    halfway between 0 (horizon) and 90 (zenith), so it's very easy to guess
    and check. From there your can try to "step through" the angles up and down
    to roughly end up where you want to get. The "known landmark" method also
    helps a lot, e.g. it's good to know that this treetop over there is 20
    high when I'm standing right here, etc.
    
    Hope that helps, for a start,
    
    
    CU!	Markus
    
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