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Archaic Astronomy and Heliacal Rising

September 10, 2005

Delphi ButtonSome time in the eighth century BC Hesiod, a farmer in central Greece, had a problem. He and his brother inherited a farm. However Hesiod had inherited the smaller share of the farm. He blamed his misfortune on his brother, Perses. Perses, Hesiod said, has bribed the magistrates. We know this because Hesiod was concerned his feckless brother was going to ruin his farm and so he wrote a farming manual. This manual, Works and Days, is possibly the oldest Greek text we have and reveals quite a lot about how the archaic Greeks saw their world. It also left Hesiod the last say in the argument and some the earliest words from ancient Greece a whinge against another man.

Perses, lay up these things in your heart, and do not let that Strife who delights in mischief hold your heart back from work, while you peep and peer and listen to the wrangles of the court-house. Little concern has he with quarrels and courts who has not a year’s victuals laid up betimes, even that which the earth bears, Demeter’s grain. When you have got plenty of that, you can raise disputes and strive to get another’s goods. But you shall have no second chance to deal so again: nay, let us settle our dispute here with true judgement divided our inheritance, but you seized the greater share and carried it off, greatly swelling the glory of our bribe-swallowing lords who love to judge such a cause as this.

Works and Days lines 25-40.

This continues for quite a while but around line 286 he says:

To you, foolish Perses, I will speak good sense.

And at line 381 he finally starts. What follows is a manual on when to perform various farming tasks.

If Hesiod had a modern calendar to hand when he wrote Works and Days, his life would have been a lot easier. However, he lived in a place that had a lunar calendar. This meant that any given month this year would start eleven days earlier next year, or possibly nineteen days later. This slide of the months against the solar year would continue, so that if Hesiod had used the names of the Greek months to plan his farming, he would have been talking about any one of at least thirty days in a year. Play the animation below to see how much a month can vary by falling 11 days earlier or 19 days later each year in just nine years.

[FLASH], 500, 100 [/FLASH]
Slide of a lunar month against a solar year.

In reality the month could have started even earlier of finished even later, what with weather or politicians manipulating the calendar for their own ends. Greek calendars would not have been very useful for agriculture and so Hesiod used other timing methods. An example is found starting at line 582

But when the artichoke flowers, and the chirping grass-hopper sits in a tree and pours down his shrill song continually from under his wings in the season of wearisome heat, then goats are plumpest and wine sweetest; women are most wanton, but men are feeblest…

He also uses the movements of snails and the flights of birds as indicators of seasons.

This is useful for a farmer. It might not have the accuracy of a modern calendar, but a farmer doesn’t just plant or harvest according to the time of year. He also changes his plans according to the current weather. If winter lasts slightly longer in a given year then he’ll plant later. Still, an accurate calendar would be handy as a general guide to the turning of the seasons. If you don’t have an accurate calendar what do you do? Hesiod also uses the movements of the stars. An example is in line 383 “When the Pleiades, daughters of Atlas, are rising, begin your harvest.”

Initially this makes little sense. The Pleiades are a star cluster and, like the Sun, they rise every day. Admittedly you can’t see them every day, as sometimes the glare of the Sun obscures them, but they are there. This line doesn’t refer to the Pleiades rising every day, but to one particular event that happens once a year, the heliacal rising.

The heliacal rising happens because in addition to rotating about its axis, the Earth makes an extra rotation relative to the stars as it orbits the sun. The means that each day the Sun obscures a slightly different set of stars.

[FLASH], 500, 375 [/FLASH]
The orbit of the Earth periodically blocks stars from view.

For an observer on Earth each day the stars rise four minutes earlier each morning and set four minutes earlier. The heliacal rising is the day when a star rises just before sunrise. It’s briefly visible over the eastern horizon and then vanishes as the sky brightens with the coming day. The first day that the star is visible in the dawn is the heliacal rising. The animation below shows the day before, when the sky is just a bit too bright before the star crosses the horizon, so it cannot be seen. Then it shows the next day when it rises just a bit earlier and you just see it before sunrise. Then it shows the day after when it rises higher into the sky before it disappears.

[FLASH], 500, 375 [/FLASH]
The day before, the day of and the day after the heliacal rising of a star.

The day of heliacal rising can vary a little. The most obvious reason is weather. Storm clouds would block out the star, but then you’d watch for it rising the next day. Even a turbulent or humid atmosphere could block out the starlight, but these conditions would make perhaps a week’s difference or less in the date from one year to the next. In comparison to the lunar calendar it it’s very accurate, and for people around the same latitude, visible at the same time.

This meant that Hesiod’s farming manual written for Boeotia, in central Greece, would have been usable for many Greeks, and therefore worth copying.

If this system could be used for farming, could it also be used to coordinate rituals? The constellation Delphinus, the Dolphin, usually rises just before rituals are performed to Apollo Delphinios. Is one a signal or omen for the other? It’s possible but there are few problems.

1. We need to show that this is a method of astronomy that ancient people were happy with. It’s not as sexy as the sun rising over a stone on a specific day. Would they have used it?
2. Was there even a constellation Delphinus in the eighth century BC?
3. They might sound similar but is Delphi, a city two thousand feet up a mountainside connected to Dolphins?
4. Is there any evidence that Delphinus, a faint constellation could be used to keep time?
5. If just Delphi that used it then it could be coincidence. Did anywhere else use the rising of Delphinus?

Well, the above is step one. This system is directly drawn from the ancient texts. So we know the Greeks used astronomy this way. But if you read through Hesiod or Homer, you won’t find a reference to Delphinus. So is it an ancient constellation or a relatively recent invention? That’s the next problem.

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