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From: Henry C. Halboth (no email)
Date: Sun Jul 24 2005 - 22:38:22 EDT
Again, have spent a couple of weeks at NC beaches and was able to
indulge myself in a number of celestial observations for Lat + Long.
By testing oneself in a known position, some idea of personal accuracy
can be obtained, as well as a real feel for the reliance which may be
placed on observations based on a sea horizon. For those who may be
interested, the following are offered .
In all, a Plath vernier sextant was employed. IC = 00'24" on the arc.
HE = 20-Ft. ZD = +4
July 5, 2005: Latitude by meridian transit - Sun's LL
LAN = 13-12-37 LMT + 4 = GMT 17-12-37
DEC = 22-43-42 N
hs 77-53-10 + corr 00-11-00 = ho 78-04-10
LAT = 89-59-60 - 78-04-10 + 22-43-42 = 34-39-32 North
July 6, 2005: Latitude by meridian transit - Sun's LL
LAN = 13-12-47 LMT + 4 = GMT 13-13-47
DEC = 22-37-40 N
hs 77-47-10 + corr 00-11-00 = ho 77-58-10
LAT = 89-59-60 - 77-58-10 + 22-37-40 = 34-39-30 North
July 8, 2005: Latitude by meridian transit - Sun's LL
LAN 13-13-07 LMT + 4 = GMT 17-13-07
DEC = 22-24-21 N
hs 77-33-15 + corr 00-11-00 = ho 77-44-15
LAT = 89-59-60 - 77-44-15 + 22-24-21 = 34-40-06 North
July 10, 2005: Longitude by time sight - Sun's LL, bearing about
111 drgrees, true
LMT = 11-36-04 + 4 = GMT = 15-36-03
DEC = 22-10-03 N
LAT = 34-40-06 N by previous meridian transit
hs 63-22-20 + corr 00-10-48 = ho 63-33-08
LHA = 26-39-15 E, by time sight formula
GHA = 50-21-42 W, by NA
Long = 77-00-57 West
July 10, 2005: Latitude by meridian transit - Sun's LL
LAN = 13-13-24 LMT + 4 = GMT 17-13-24
DEC 22-09-32 N
hs = 77-20-20 + corr 00-11-00 = ho 77-31-20
LAT = 89-59-60 - 77-31-20 + 22-09-31 = 34-38-11 North
July 12, 2005: Latitude + Longitude @ LAN by equal altitudes
+ reduction to meridian
1. For the Longitude
AM obs @ chro time = 17-00-12; Sun's LL = 76-42-00
PM obs @ chro time = 17-26-59; Sun's LL = 76-42-00
Mean chro time of obs = 17-13-35.5 = GMT of LAN
GHA Sun @ 17-13-35.5 = 76-59-06 West = Longitude
2. For the Latitude
hs Sun's LL @ 17-00-12 = 76-42-00
DEC = 21-53-12 N
GMT of LAN by equal altitudes = 17-13-35.5
Time of obs before LAN = 17-13-35.5 - 17-00-12 = 00-13-24
Altitude corr to meridian - Bowditch Tabs 29 + 30 = + 00-19-36
hs 76-42-00 + 00-11-00 + 00-19-36 = ho 77-12-36 @ transit
LAT = 89-59-60 - 77-12-36 + 21-53-12 = 34-40-36 N
3. Position @ 13-00-12 LMT = Lat 34-40-36 N + Long 76-59- 06 W
Note: If one were to "analyze the analyzed analysis", and, if the
assumed correct Longitude given below is absolutely correct,
there is roughly a 4.5 sec discrepancy in this solution, indicating
possibly some unaccounted for chronometer or sight timing error -
perhaps a combination of both.. However, as subsequently stated,
I cannot be absolutely sure of the charted Longitude, nor can I deny
the possibility of a small error in timing. There are a number of ways
to resolve this error, but they seem to be beyond the purpose of
this posting.
July 14, 2005: Latitude by meridian transit - Moon's UL
LTT = 19-13-36 + 4 = GMT 23-13-36
DEC = 10-55-40 S
hs = 44-06-20 + corr 00-19-24 = ho 44-25-44
LAT = 89-59-60 - 44-25-44 - 10-55-40 = 34-38-36 North
I was in position 34-40.073 N + 77-00.097 W. I cannot vouch for
the accuracy of this position, as the location is somewhat off
the beaten path, and may not be well charted on the map program
available to me. Unfortunately, I do not have a GPS to verify it.
Regardless, it is my opinion that these results demonstrate the
average accuracy + repeatability attainable by celestial navigation,
under good to average conditions, utilizing the sea horizon.
As previously reported, the horizon used, at the edge of the
Gulf Stream, is plagued with a light haze which may have induced
a bit of foreshortening, with resultant altitudes a somewhat greater
than true.
I am surprised at the apparent accuracy demonstrated in the
equal altitude solutions shown. I did experiment with equal
altitudes many years ago at sea, and it is my recollection that
results were comparable. It might prove interesting and informative
if some of our members who employ an artificial horizon would
give equal altitudes a try and report accordingly. Their value may
be being understated in available literature as well as on this List.
Henry
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