NavList:

   

Reply

On 2018-05-17 11:15, Ed Popko wrote:
> Look towards the bottom in the final steps.  The example shows Apparent Time 
at the Ship to be 3:56:42 and Greenwich time 7:45:27. Given the date above, 
1880, we know we are dealing with GMT Civil Time or 12:00:00 at noon.

I don't think so. Didn't the Almanac in that era follow the astronomical
time convention? I.e., GMT was 12 hours behind Greenwich Civil time. In
a controversial step adjustment, GMT changed to the civil time
convention at the beginning of 1925.

In the example from Lecky, ship time is 1880 June 25, "about 4 p.m." At
the observation, the chronometer reads 7:47:57 after correction for
rate. Longitude by DR is 57 12 W, so GMT (modern style) is about 4 hours
ahead of local time. Thus chronometer time corrected for rate is
19:47:57 GMT modern style, or 07:47:57 GMT old style, June 25 in both cases.

At that time I get these values from the USNO MICA software:

14 05 14.2 Greenwich apparent sidereal time
  6 19 47.0 Sun apparent right ascension
----------
  7 45 27.2 Greenwich apparent solar time (old style)

That matches the "Apparent Time at Greenwich" near the bottom of the
page in Lecky. Since I calculated solar time in the old style, the
12-hour adjustment required by the modern style isn't necessary. In
other words, old style apparent solar time is simply the GHA of the Sun.

   

Reply