For any who haven't opened the attachments,
here is Patrick Goold's message, slightly edited
for formatting, with a table replaced by
commas:
BEGIN-----------------------------------------
I.
Determining the time of the meridian passage.
Norfolk, Virginia. 22 January 2011.
I was confident it was sometime well after
noon local watch time but I found I could not
make sense of how to use NA�s equation of time.
NA gives mer. pass. as 12 hrs. 11 m and the
equation of time for noon as 11 m 29 sec. (I
inferred from Bowditch that I should add these
two. But adding them gives a value outside the
range of possible variation.) The website
timeanddate.com put LAN at Norfolk, Va at 12:17.
I used this as my initial estimate.
I recorded five shots, all lower limb sun
shots. The first two I made at set times and
recorded the angles. The last two I waited for a
return of the second and then the first
altitudes, recording the times when this
occurred..
Sight(WT), Hs, Ha, Ho
noon, 66� 16�, 33�
08�, 33� 22.8�
12:15, 66� 36�, 33� 18�, 33�
32.8�
12:17, 66� 35.6�, 33� 17.8�, 33� 32.6�
!?!
12:19:23, 66� 36�, 33� 18�, 33�
32.8�
12:34:20, 66� 16�, 33� 08�, 33�
22.8�
Because I am using an artificial horizon I
made no dip or altitude corrections. Ha is just
Ha divided by two. Ho is Ha plus 14.8 for lower
limb correction.
The noon sight and its mirror altitude sight
gave an average of 12:17:10. The 12:15 sight and
its mirror average to 12:17:12. The average of
those two averages is 12:17:11. My time zone is
GMT plus five. So I made out meridian passage at
my site as occurring at 17:17:11 GMT.
II. Determining Latitude
Zenith distance = 90� - 33� 32.8� = 56� 27.2�
N
Dec (tab) = S 19� 38.5�
d = .06 d corr =
0.4�
Dec = S 19� 38.9�
Latitude = z - Dec = 36� 48.3� N
III. Determining Longitude
GHA (hr) = 72� 06.8�
GHA m/s = 4�
17.8�
GHA = 76� 24.6�
Longitude = GHA = 76� 24.6� W
According to my handheld GPS, a Garmin GPSmap
76Cx, my location was actually
36� 50� N
76� 21.7 W
for a difference of 1.7� of latitude and 2.9�
of longitude.
Conditions were somewhat less than ideal and
accuracy may have suffered. Obviously there is
something wrong with the middle of my five
sights. It was a very windy day and the glass
covers on the Davis artificial horizon permit
some drafts to intrude and disturb the
reflective surface. It was a very cold day (-4
C) and this made for some fogging of the AH and
perhaps of sighting scope. Finally, there was a
haze becoming clouds and overcast as the
sighting progressed.
END-------------------------------------------
Just to reiterate, everything between the
"BEGIN" and "END" above is from Patrick
Goold.
-FER
----------------------------------------------------------------
NavList
message boards and member settings:
www.fer3.com/NavList
Members may optionally
receive posts by email.
To cancel email
delivery, send a message to
NoMail[at]fer3.com
----------------------------------------------------------------