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Subject: Re: Relative Importance of Accurate Timing of Sight for Lunars versus Altitude Sights
From: John Kabel (jjkabel@XXX.XXX)
Date: Tue Jun 10 2003 - 07:29:50 EDT
I agree. When I was studying celestial, I didn't get really good until
I got the mechanics of timing the sights down pat. I ended up with my
watch with its face on the inside of my left wrist. I would swing the
sextant and start a chant of "and one and two and three ... " as the
body touched the horizon. Then an immediate glance to the watch while
pressing the sextant light, which illuminated the watch somewhat,
correcting the observed time for how far I got in my chant. At that
point I read and recorded the angle and the time on a log sheet.
When my observation plans matched reality, on a few nights, I got to 50
s per sight, 45 to 50 or so sights in a row. The watch would be
carefully compared with a radio time signal, and I was keeping track of
its drift day by day, on a chart. I could predict error fairly
accurately. Only once all these pieces came together did I get any
sights under 0.5 ' at a known land position. Then I started expanding
the conditions of sights, to partly cloudy twilight, artificial
horizons, etc., to build up more practice.
It must have worked, because I passed. And still enjoy the use of my
sextant to this day.
Great discussions on the list lately, folks!!
John Kabel
London, Ontario
> It has taken me a long time to where I can consistently get my altitude
> sights to under 0.5' of arc from a known position on dry land, often,
> now, under 0.2' of arc. A critical component of that has been judging
> the exact moment of contact and hitting the stop watch accurately at
> that moment. After setting the angle, I generally wait for the object
> to converge with the horizon, or itself in the artificial horizon, and
> try to hit the stop watch when contact occurs.
>
> However, I always had a fair amount of luck with lunars, even before
> improving my timing technique for altitude sights. That was back when
> I would look down at my watch after perfecting the contact and record
> the time.
>
> I still prefer this second method for lunars and believe it is the best
> for that observation. That is because 12 seconds of time elapse, more
> or less, between each shift of 0.1' of arc in a lunar. It doesn't make
> much difference whether you're 2-4 seconds out. It's much more
> important to get the angle measured to the utmost precision possible
> than to time the sight accurately. You need to concentrate much more
> on proper manipulation of the micrometer than on the time, like when
> checking index error by determining the semi-diameter of the sun.
>
> Any comments?
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