Re: Estimating "Miss Distance"

From: Peter Wakelin (
Date: Thu Apr 30 2009 - 18:17:26 UTC

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    To one Peter from another,
    In a recent message I recall your saying you used several pairs of
    binoculars.  With differing fields of view this must make estimating
    star separation very difficult.  I strongly recommend you stick to one
    Double star separations are usually measured in arcseconds which is too
    small.  There is a useful field in the bottom left corner of the
    ObsReduce screen that gives the separation of two marked stars which you
    could use to get an idea of what, say, 10 arcmin looks like in your
    field of view.  With a little experience you will then be able to
    estimate appulse distances to within about one arcmin up to distances of
    about 5 arcmin.
    In the ObsReduce mode I use, ie, azimuth / elevation, position angle is
    measured clockwise from the direction of the zenith.  This is probably
    not the case with the recently introduced 'north = up' mode though.  You
    don't need to enter the position angle but you may need to add 180 to
    the stated value if the satellite passed on the other side of the star
    to that predicted by ObsReduce.
    I hope this is helpful.  I must say I'm very impressed with your rapid
    progress and we certainly need more, younger observers as many of the
    most prolific ones are approaching age 70 and will inevitably start to
    'fall off their perches' in the not too distant future.
    Best wishes,
    In message <>, writes
    >Hi all:
    >Using 15x70 binoculars and trying to use appulses, reducing with Ted  
    >Molczan's ObsReduce--I've realized my eye isn't well-trained to estimate "Miss  
    >Distance" with this instrument.  So far, I've been trying to estimate  
    >distances by my recollection of "Jupiter Diameters"  To see if it helps  any, 
    >going to observe a list of appropriate double stars.  If anyone  has used 
    >other strategies to address this, I'd appreciate knowing about  it.  Also, in 
    >ObsReduce, is PositionAngle (for appulse) measured from true  north or from 
    >apparent "12 o'clock?"
    >Peter Gertson
    >Cospar 8039
    Peter Wakelin
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