From: roelle@uars_mag.jhuapl.edu (Curtis Roelle)
Subject: Re: Old astronomical events
Organization: Johns Hopkins University
Date: 11 Dec 92 20:41:22 GMT

wbb@hpcuhe.cup.hp.com (Bill Buzbee) writes:

>   Can anyone out there help me find some about some old astronomical
>   events?

>   One of my hobbies is collecting old books.  Because I'm not rich,
>   though, sometimes I can only afford single leaves of old books and
>   manuscripts.  A while back I picked up a page from a mid-16th
>   century book which, in Latin, described the following:

>       o  A solar eclipse on September 18, 760 a.d. at 9:00.

>       o  A solar eclipse the following year (761) on the fourth
>	  of the month (probably Sept.) at 6:00.  [My Latin
>	  isn't very good; this could have meant a lunar eclipse
>	  on September 4, 761.]

I have a preprint version of Volumes I and II of _The Moon's
Acceleration And Its Physical Origins_ by the late Robert R. Newton.
Ths work was published by the Johns Hopkins University Press.  My copy
of Vol. I, subtitled _As Deduced From Solar Eclipses_, is dated
December, 1977; Vol. II, _As Dedeced From General Lunar Observations_,
is dated 1984.  Last year he passed away on June 2, 1991.

Table XIII.13 in Vol. I, "Coefficients of Condition For Eclipses from
702 to 841", updated in Table A.I.9 in Vol. II, includes two solar
eclipses in the years 760 and 761, designated as:

			760 Aug 15 E, CE
			760 Aug 15 M, B
			761 Aug 5 C,
where:
  E = England
  CE = Central Europe, including Austria, Czecholslovakia, and Switzerland
  M = Countries around the eastern Mediterranean, including Greece
  B = Byzantine Empire
  C = China

Vol. I indicates that the 760 eclipse was observed in Gottweih (Table
XI.1) and Constantinople (Table XII.1).  Other than this, no other
information except for the sources are given by Newton for the 760
eclipse.

The 761 eclipse was viewed in heartland China and Newton provides a
sketch of the path in Figure III.2.  Newton defines the Chinese
heartland as "a rectangle extending from 31N to 34.5N and from 108.95E
(the longitude of Charng-an) to 117E."

Newton makes several references to the 761 eclispe when discussing two
1975 works by Muller and Stephenson (MS) and Muller (M).  He considers
their assumption that during years of revolution, the astronomers fled
with the emperor to a location where the recorded eclipse observations
were made.  In summary, Newton writes in Vol. I Chapter III,

"..M and MS conclude that an observation appearing in an astronomical
treatise was made at the capital unless there is a specific statement
that the observation was made somehwere else.  However, they then
attach a special meaning to 'capital'.  They cite the eclipses of 756
October 28 and 761 August 5, which both occurred during a prolonged
period of revolution when the emperor was not able to be in his
nominal capital.  However they find that both were complete at the
place where the emperor was temporarily residing.  From this they
conclude that the records in the astronomical treatises were made by
the imperial astronomers who, as M [p. 8.45] picturesquely puts it,
'are _always_ with the Emperor, even when they must pack bag and
baggage, and go into hiding at the remotest edge of the Empire!'
Hence, M and MS use the term capital to mean the place where the
emperor was at any particular moment, and I shall follow their usage
in this immediate discussion.  When I need to refer to the city which
was the usual capital, I shall refer to the nominal capital...

"M and MS use the Tarng eclipses of 756 October 28 and 761 August 5 to
prove ... that eclipses in the treatises were observed only where the
emperor was, and not 'anywhere in China'.  The revolution mentioned
above began in 756 and was not completely put down for many years.
Both these eclipses were total and at both times, according to M and
MS, the eclipse was not total at the nominal capital although it was
total where the emperor happened to be.

"Let us take up 761 August 5 first because it is the easier case to
discuss.  The zone of totality for this eclipse passes through
heartland China although it missed the nominal capital.  Therefore it
proves nothing relevant to the point of M and MS"

Newton goes on to examine records of several other eclipses recorded
by the chinese, and then makes his point that,

"As it happens, for the eclipses that are involved in testing the
place where the observations are made, the emperor was at the nominal
capital, so far as we can tell.  Hence, there is no disctinction
between the nominal capital and the capital in the sense of MS and M."


I hope this helps you.  Newton gives August rather than September as
the month for both eclipses in 760 and 761.  Also, the former was
visible in Central Europe while the latter was visible in heartland
China, and so apparently neither location would have observed both
eclipses.

Curt Roelle roelle@sigi.jhuapl.edu