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Kieran Kelly wrote:
> My main worry is the errors in the Nautical Almanac for the period,
> which have come to light on this site. An example calculation is shown
> below. I wonder if one of the list members could run the calculation
> though modern software and check for accuracy.

The JPL HORIZONS web app can calculate the quantities you need:
http://ssd.jpl.nasa.gov/cgi-bin/eph

For example, here's sunrise on Mount Wilson, California, on 4 July 1856:

  Date_(ZONE)_HR:MN     R.A.__(r-apparent)__DEC Azi_(r-appr)_Elev
****************************************************************
  1856-Jul-04 05:34 C   06 52 44.72 +23 15 57.0  59.7344  -2.1839
  1856-Jul-04 05:35 C   06 52 44.70 +23 15 53.5  59.8800  -2.0053
  1856-Jul-04 05:36 C   06 52 44.69 +23 15 50.0  60.0253  -1.8264
  1856-Jul-04 05:37 *r  06 52 44.67 +23 15 46.6  60.1702  -1.6473
  1856-Jul-04 05:38 *   06 52 44.65 +23 15 43.1  60.3148  -1.4679
  1856-Jul-04 05:39 *   06 52 44.64 +23 15 39.6  60.4591  -1.2883

Letter C after time means civil twilight. Letter r means sunrise,
allowing for dip and refraction. Asterisk indicates "solar presence".

Those are refracted apparent coordinates. With no refraction, the last
line becomes:

  1856-Jul-04 05:39 *   06 54 56.50 +22 51 28.2  60.4591  -1.9349

Note that RA and dec are affected by refraction, so to compare its
output to an almanac, HORIZONS should be run in "airless" mode.
Differences in reference frame and time scale may have to be considered too.

Operating HORIZONS via email is more complicated but allows finer
control than the web interface. For example, email allows time steps
smaller than 1 minute.

   

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