Now, grant me that nothing that happens to the sun is so like its setting as a solar eclipse. You will if you call to mind this conjunction recently which, beginning just after noonday, made many stars shine out from many parts of the sky and tempered the air in the manner of twilight. If you do not recall it ... (ref.1, chapter 19)
There is no information neither where this eclipse was observed, nor when it was observed. But the appeal to remember is addressed to all participants of the dialogue, who apparently are from different places in the Roman empire such as Italy, Greece and Egypt.
What we are looking for is an - at least - annular solar eclipse with a maximum at noon over at least one of the urban centers of the antique world during the adult lifetime of Plutarch.
The commonly agreed to dating
Stephenson and Fatoohi (ref. 2) consider four possibly total solar eclipses in the central or eastern Mediterranean during the assumed lifetime of Plutarch (RomAD 46 to 120), and argue that the observation should be connected with the solar eclipse of 20 March 71 over Greece: (about year count and notation read explanation here, opens in new tab)
Fig.1.: The commonly agreed to solar eclipse corresponding to the observation of Plutarch. Visualized using the Nasa Eclipse Web Site .
Because of the 23° east offset from Greenwich, the local time of the maximum of this eclipse can be calculated to 09:26 + 1:34= 11:00. From the picture we can also see that the altitude of the sun changed from 37.8° through 47.8° and ended at 50.7°. The report saying "beginning just after noonday" is then not a very exact description of the eclipse.
Furthermore, the totality of this eclipse would have been visible only in Athens and the south-eastern part of Greece, which dramatically limits the number of participants in the dialogue who could have been eye witnesses and would remember the event.
With our 232-hypothesis in mind, we might question whether Plutarch actually was in Athens on 20 March 71.
Looking for an alternative dating
According to our 232-hypothesis, Plutarch would have lived in the period 278 to 352 and we would expect a major solar eclipse over the Mediterranean within that period.
Fig.2.: A solar eclipse corresponding to the observation of Plutarch, if his lifetime is redated by 232 years.
The annular eclipse of 17 July 334 was an event at noon (see the change of sun altitude above, also add one hour to the UT-times to get the local time) visible from Rome, Campania, southern Greece and Alexandria. It is actually a much better match towards the observation of Plutarch than the one suggested conventionally. "Everybody" would have seen it, and we may actually wonder why there are no reports of this eclipse with its "true" date. The only instance where we have found that this eclipse is mentioned is in the Mathesis, a book on astrology by Firmicus Maternus (ref.3).
About the Theon participating in Plutarch's dialogue
The above cited report of the solar eclipse continues as follows:
If you do not recall it, Theon here will cite us Mimnermus and Cydias and Archilochus and Stesichorus besides and Pindar, who during eclipses bewail 'the brightest star bereft' and 'at midday falling' and say that the beam of the sun 'is sped the path of shade'; and to crown all he will cite Homer, who says 'the faces of men are covered with night and gloom' and 'the sun has perished out of heaven' speaking with reference to the moon and hinting that this naturally occurs when waning month to waxing month gives way. (ref.1, chapter 19)
This Theon is recognized as the literary expert of the dialogue, and he lives in Egypt (ref.1, chapter 25). If the solar eclipse discussed is the one of Astr 334, this Theon could be identical with the young Theon of Alexandria, the man from the Mouseion who later reported a unique solar eclipse. This eclipse could be retrocalculated to Astr 364 (ref.4) and therefore placed Theon on the astronomical timeline.
Even more intriguing is the fact that Ptolemy, working in Alexandria, refers to a "Theon the mathematician" making astronomical observations in Alexandria, in his Almagest. As Ptolemy's lifetime is assumed to be RomAD c.85 to 165, and the Almagest (his earliest work) was finished about RomAD 150, this Theon is assumed to be Theon of Smyrna. But Theon of Smyrna was rather living in Smyrna instead of Alexandria, and he was not known to be an outstanding astronomer (ref.5).
However, if we redate Ptolemy's lifetime with 232 years according to our hypothesis, he would have lived c.317 to 397 and thus been contemporary and colleague with Theon of Alexandria (c.335 to 405). His Almagest (redated c.382) could have referred to Theon's observations, and Theon could have written his commentary on the Almagest after the latter was finished.
1. Plutarch, De facie quae in orbe lunae apparet, English translation by Cherniss (1957).
2. Stephenson F.R, Fatoohi L.J., The Total Solar Eclipse Described by Plutarch. Histos 2 (1998) p.72-82. download here
3. Firmicus Maternus, Mathesis, 1st book, chapter 4:10. read here
4. Stephenson F.R.: Historical Eclipses and Earth's Rotation, Cambridge 1997.
5. O'Connor J.J. and Robertson E.F. 1999. Claudius Ptolemy. School of Mathematics and Statistics, University of St Andrews, Scotland. read here