Next message: Frank Reed: "ebay: Navigation School Workbook 1886"
Greg, you wrote:
"It seems to be +/- 1 minute of arc. I can't tell where the error comes from
- but in the end it comes out within +/- 1 min of my MAC."
That's excellent. Honestly though, even your M.A.C. may not be that accurate
over its whole range. Have you tested your octant for large angles? Say,
above 70 degrees?
You asked:
"but lets say on the avg, to the nearest min. My experiments with running
the calculations, shows varying the Ho or Lat by 1min can move the AP about
4 miles. There are different combonations; Ho+ Lat=0, H0+ Lat+, Ho- Lat -,
etc., etc. some give better results; but 4 miles is a safe number when
speaking of errors.
Was this as good as it got ( Talking in period c 1800 if using a octant or
sextant with this resolution)? and didn't you need to resolve down to 10"
or 20" to do lunars?"
A mile or two accuracy in latitude was (and still is today) a reasonable
expectation. Even a perfect sextant with perfect input data is still limited by
the vagaries of terrestrial refraction which makes the horizon variable by
about one minute of arc. Note that sextants were developed specifically to
measure large angles and to measure them at an accuracy about ten times better
than you can do with an octant. Octants were used for measuring altitudes.
Sextants were used for measuring lunars (which are not affected by terrestrial
refraction). After 1850 (-ish) sextants were used for more or less all
observations.
-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
