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Robert Eno asked:
"Can anyone tell me at what  point in time navigators moved from using right
ascension to sidereal hour angle  for reckoning celestial coordinates?"

In 1933 an experimental American  Air Almanac was published which used
GHA/SHA instead of RA (or so they say --I  haven't seen it). Though this early air
almanac was not continued, some of its  features were incorporated into the big
revision of the American Nautical  Almanac in 1934. In this year, the
appendix on calculating geocentric lunar  distances was finally dropped along with
some other flotsam, and for the first  time ocean navigators found GHA in
parallel with RA. Those who wanted to could  now use GHA, while conservative
navigators could stick with Right  Ascension.

In the late 1930s and early 1940s, various countries began  regular
publication of air almanacs and these apparently used GHA/SHA  exclusively with short
intervals between tabulated values (e.g. GHA given every  ten minutes). This
allowed "eyeball interpolation" and shortened the work by a  few minutes per
sight. For air navigation every second counts.

The  American Nautical Almanac was again revised in 1950 and from this date
it  broadly resembles the modern Nautical Almanac with GHA/SHA tables and no
more  Right Ascension. This is also the year that the cardboard orange cover
appears.

Meanwhile across the Atlantic, the "Abridged Nautical Almanac",  which was
the standard almanac for British mariners, was not revised during this  whole
period. In 1953 there was a major revision of the AbNA which finally  replaced
RA with GHA/SHA. This year also marked the beginning of serious  attempts to
create a common, unified almanac. After considerable negotation the  American
Nautical Almanac and the (British) Abridged Nautical Almanac were  unified in
1958, mostly along the lines of the American almanac. The titles  remained
separate until 1960 when the astronomers' almanac finally lost its  nautical title
and the combined mariners' almanac could recover the logical  title: The
Nautical Almanac.

Modern celestial navigation reached its apex  in 1958. The new, drastically
revised Bowditch was released that year. And the  Nautical Almanac achieved its
final, modern form. Apart from the inclusion of  sight reduction tables
starting in 1989, there have been almost no changes to  the almanac since the
pivotal year 1958.

-FER
42.0N 87.7W, or 41.4N  72.1W.
www.HistoricalAtlas.com/lunars

   

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