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George Huxtable wrote:
> That's an odd way to denote a Greenwich time after Greenwich noon, isn't it?
> Remember, in those days, the Greenwich day started at Greenwich mean noon,
> so 0 hrs GMT for 24th April corresponded to noon, halfway through the civil
> day of  24th April. That was the way Greenwich dates and times were noted in
> almanacs of that era, recorded in Astronomical Time, which ran 12 hours
> later than ordinary civil time.

You're correct that zero hours astronomical time came 12 hours after
zero hours civil time of the same date. But that made the astronomical
time of an event 12 hours *earlier* (i.e., less than) than the
corresponding civil time.

One way to remember the difference between the astronomical, civil, and
nautical day is to arrange the names in alphabetical order: 0000
astronomical = 1200 civil = 2400 nautical (same date for all).

The change to the meaning of GMT commencing in 1925 was controversial.
For example, in 1921 The Observatory published several letters to the
editor on the subject:

http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?ref_stems=Obs....44&jou_pick=YES&return_req=no_params&end_year=2009
(Search the page for the word "time", and note that the articles are in
reverse chronolgical order.)

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