Part One showed the heliacal rising of Sirius in our time and in the Egypt of 2000 BC. Part Two was about geometrical vs. observed events, calendar shift, and heliacal setting.
The Pleiades
Whereas Egypt is one long narrow river valley incised across the world’s largest desert, Greece is a salad of peninsulas and islands, and the season to be watched for was the sailing season. The heliacal rising of the Pleiades was the signal that it was safe, or safer, to put out into the Aegean Sea. Plein, “to sail.”
Let’s use Athens, the chief maritime power. For the date, we might use the “golden age” of Athenian democracy, drama, literature, philosophy, and architecture, between 480 and 400 BC.
I thought of choosing 700 BC, around the time Hesiod composed his epic Works and Days. It is a farmers’ manual, preserving lore on, for instance, the seasons at which to plant crops. For that earlier year, the heliacal date would be 3 days earlier. Hesiod lived in Boeotia, an inland region – whose chief city was the other great Thebes. The distance of little more than 30 miles from Athens would make little difference.
What makes more difference is that the Sun passes much closer to the Pleiades (only about 3° north of the ecliptic) than to Sirius (about 40° south of the ecliptic). And the magnitude of the cluster is about 1.6, as against Sirius’s -1.46, meaning that the combined light sent to us by the seven stars is about 16 times weaker; and it is spread out (with low “surface brightness,” like a nebula). The Pleiades, about 400 light-years from us, are the most readily noticed deep-sky object, but much less readily than the one piercing star.
So the delay from the geometrical rising of the Pleiades, at April 18, to the first actual sighting would surely have been longer. And indeed the sailing season is said to have started in May.
And to have lasted till the heliacal setting of the Pleiades in November. No.
The heliacal setting was only a few days later, April 22. In our sky scene, the arrow through the Sun is its motion over 5 days, against the starry background. You can see that it won’t take the Sun long to get past the Pleiades, to where they will be level on the sunset horizon.
In May and on through summer, the Pleiades were higher at each dawn; in October they were on the meridian at midnight.
What happened in November was the heliacal rising at sunset, on the horizon opposite from the setting Sun!
The geometrical heliacal rising at sunset was on October 16. Then at each following sunset the Seven Sisters became higher, calling attention to themselves – “Don’t look west at the sunset, here are we over in the east!” – reminding fishers that November weather was coming. The Etesian north-easterlies of summer, that could waft them home, were about to die down.
It needs to be mentioned that translating ancient Greek dates into our calendar is a headache for scholars. Each district or city-state had its own calendar.
More
The subject could ramify on. Apparently the Maori began their year with the heliacal rising of the Pleiades – in June. Good old Allen’s Star Names quotes these bits from Hesiod:
Forget not, when Orion first appears,
To make your servants thresh the sacred ears
And:
When in the rosy morn Arcturus shines,
Then pluck the clusters from the parent vines
In 700 BC, the heliacal rising of Betelgeuse would have been in mid June, or the end of June for the whole figure of Orion; that of Arcturus, in September.
And there are probably many others such references to be found. But enough for now.
To be continued
I think we need a fourth, empirical part to this subject: how to look for actual heliacal events in the coming year.
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