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## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Predicting transit using Bowditch section 2010
From: Jim Thompson
Date: 2003 Dec 22, 15:55 -0400

```I second that.

By the way, below is my prediction for transit of the sun from the east end
of the Dominican Republic on February 3/04.  All 3 methods give the same

The sun and stars line up very nicely for my compulsory evening twilight
3-body sight while we are down there for a week of R&R.  I hope Customs in
the DR doesn't balk at the sextant and GPS unit in my luggage.

Jim Thompson
jim2{at}jimthompson.net
www.jimthompson.net
Outgoing mail scanned by Norton Antivirus
-----------------------------------------

> -----Original Message-----
> [mailto:NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM]On Behalf Of Fred Hebard
> Sent: Monday, December 22, 2003 3:27 PM
>
> Doug,
>
> Having somebody present these techniques is precisely why I am on this
> list.  If you can, I would appreciate hearing of any you wish to share.

Punta Cana Predicted Transit Sun on Feb 3/04
12h  47m 14s

Airport
L 18d 34.584' = 18.5764d
Lo 68d 21.804' = 68.3634d

Method 1:
L 18d 34.584' = 18.5764d
Lo 68d 21.804' = 68.3634d
GHA 68.3634d
Next lowest GHA 561d 33.3' = 56.5550
Whole GMT hour of lower GHA = 16
DLo 68.3634 -  56.5550 = 11.8084d
Increment 11.8084d = 11d 48.5' = 47m 14s
=> Time of transit GMT = 16h  47m 14s
ZD +4
Time of transit ZT = 12h  47m 14s

Method 2:
Meridian Passage almanac = 12h 14m that day.
DLo 8d 21.8' = 33m 27s past central meridian = 33 min.
=> Transit is 12h 47m +/- 1 minute.

Method 3:
Greenwich:
Lo 00d 00.0' = 00.0000d
GHA 00.0000d
Next lowest GHA 356d 33.6' = 356.5600
Whole GMT hour of lower GHA 12
DLo 360.0000 - 356.5600 = 3.4400d
Increment 3.4400d = 03d 26.4' = 13m 46s
=>Time of transit GMT = 12h  13m 46s which rounds to Almanac's 12h 14m.
ZD +0
Time of transit ZT at Greenwich = 12h  13m 46s.
Add DLo 8d 21.8' = 33m 27s past central meridian.
Time of transit ZT at Airport = 12h  47m 13s.

EqT = (shaded so negative value)
1200 -13m 46s
0000 -13m 52s that night
1600 -13m 48s interpolated
Subtact EqT from GMT to get GAT, since meridian passage is after 1200, but
since EqT is negative, then add its absolute value to GMT to get GAT, which
is logical.

```
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