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Venus ex-mer backsight dipshort
From: Jeremy C
Date: 2011 Jan 16, 01:41 EST
From: Jeremy C
Date: 2011 Jan 16, 01:41 EST
You HAD to ask for that Greg. Well, since you did, and I happen to be
in the proper place to do something completely off the wall like that, I
did. I will say that I didn't like the results. I can
think of three main sources of error:
1) i didn't get the apex of the arc when swinging the
sextant for azimuth. There were some clouds so I am not 100% sure with
this.
2) Dip short is incorrect. The shoreline at
that bearing slopes away from me steeply so the range changes quite a bit with
azimuth. I might have the range wrong and at 106 ft and 1.x miles, it's a
big correction.
3) Math blunder. It's been ages since I've
done a back sight, so i might have loused up the math somewhere along the
lines.
For those who are daring enough to try this sight, I'd like to see the
following to see if I did something wrong.
1) "A" for the ex meridian
2) The correction to Ho for the ex-meridian
2) Dip short correction
3) Latitude
I'm actually really curious to see your math from Hs to final Ho to see if
I did this right at all if people are willing to type it all out.
So here it is, an Ex-meridian backsight, dip short of Venus during the
day:
Date: 16 January 2011
ZD -6
Lat 7 deg 16.3' South
Long 72 deg 26.8 East
Height of eye 106 feet
Range to shore 1.25 n miles
Index error 0.8' on the arc (normally an IC of -0.8)
Hs observed 102 deg - 20.5' to the shoreline
Time 10h 08m 52s Local time.
My Lat was 7deg 8.3' South which is obviously a big error (8
minutes).
In a message dated 1/14/2011 7:44:39 P.M. Central Asia Standard Time,
gregrudzinski@yahoo.com writes:
Jeremy,
Excellent assortment of CN on your last trip. On my short list of unusual observations to try is a daytime Venus ex-meridian/transit back-sight with a dip short horizon. Maybe you can try some back-sight exotica on your next trip and post the reductions. It looks like extra care is needed for this type of sight.
Greg Rudzinski
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