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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Relative Importance of Accurate Timing of Sight for Lunars versus Altitude Sights
From: John Kabel
Date: 2003 Jun 10, 07:29 -0400
From: John Kabel
Date: 2003 Jun 10, 07:29 -0400
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?