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In a 1917 issue of The Observatory I saw this letter complaining about
the definition of sunrise and sunset in the tables of an ephemeris. I
must admit my inability to grasp the "parity of reason" in his argument,
but it does show that "obvious" notions of rise and set are not
universal. (The "Companion" mentioned in the letter apparently refers to
a supplement to the magazine.)

"There can be little doubt as to the usefulness of the tables of rising
and setting of the Sun and Moon, lately published as a supplement to the
American Ephemeris... From the figures in these tables it appears that
sunset is defined as the instant when the upper limb is on the visible
horizon. This, therefore, implies that sunset does not happen until the
whole of the disc has disappeared, and it might be expected by parity of
reason, that sunrise should not happen until the whole of the disc has
reappeared, but in these tables, on the contrary, the times given are
again those when the upper limb is on the visible horizon. By defining
sunset or sunrise as the instant when the centre of the disc is on the
visible horizon, as is done in your 'Companion,' any inconsistency of
this kind is avoided."


http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1917Obs....40..345H&db_key=AST&page_ind=0&data_type=GIF&type=SCREEN_VIEW&classic=YES

A later letter supports the "upper limb" definition:


http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1917Obs....40..410O&db_key=AST&page_ind=0&data_type=GIF&type=SCREEN_VIEW&classic=YES

   

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