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We know that the Arctic circle experiences 6 months of continuous day light during the sun’s apparent northward journey (to the solstice) and vice verse for the Antarctic region. This is attributed to the tilt in the earth’s axis.

In the case of ancient models, the earth was not considered to be tilted and in some cases, not even a sphere (models before Ptolemy).

How then did these ancient models explain 6 months continuous sunlight and darkness at the respective poles?

Note: If they said that the sun simply moved north or south to shine directly there, it doesn’t explain the fact that the climate up there would still be cooler than at the equator. So also, how did they explain the climate being cooler, yet accounting for the 6 months of day and night?

Adiyarkku
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    Actually on the Arctic circle, the "24 hours of daylight" only occur for a short time around midsummer. To get six months of light you need to go the pole (and nobody in ancient times got anywhere near either pole). More generally few literate people in ancient times were aware of much north of about 50⁰. – James K Oct 15 '23 at 16:46

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First let me clear up what seems to be a misunderstanding: At the time of Ptolemy (100–168 AD), people had regarded Earth as spherical some 700 years back in time: According to the biographer Diogenes Laertius (~3rd century BC), the first to call Earth a sphere was Pythagoras (570–495 BC), although it was more likely his contemporary, Parmenides (~500 BC).

The Greek polymath Eratosthenes (c. 276–195 BC) famously calculated Earth's circumference and he also, as the first, calculated correctly the tilt of Earth's axis.

But if you go further back in time, both through the Greeks Xenophanes (c. 570–478 BC), Anaximenes (c. 586–526 BC), Anaximander (c. 610–546 BC), and Thales (c. 626–548 BC), and to Egyptians, Babylonians, and Chinese natural philosophers, it is true that the preferred model of the Earth was a flat, or semi-flat (shield-shaped), disk-like mass floating in either space or water. And it is true that in this model, you cannot explain the difference in the length of the day on different latitudes1,2.

So the answer to your question is: They didn't.

Natural philosophy at this time was dominated by Mediterranean and Middle Eastern civilizations, and although they did travel, their journeys were more in the east-west direction than in the north-south direction.

As I've mentioned in this answer about Aristotle's arguments for a round Earth travelers from the north did report shorter days, and journeys from east to west seemed to take a shorter time than the opposite direction (because the travelers followed the Sun's direction). However, these arguments weren't really used by Aristotle, possibly because he didn't trust any observations but his own.

1 Well, to some extent you can on a shield-shaped Earth, and if you're a modern flat-earther you can claim that the Sun shines like a flashlight in whichever direction fits your model.

2 Note also, as James K comments, that your premise is slightly inaccurate, as a six months of 24-hour daylight/nighttime only occurs at the poles, whereas the closer you get to the polar circles, the fewer days of constant darkness/light you will have.

pela
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  • And how does Ptolemy explain the 6 month thing using his geocentric model? – Adiyarkku Oct 15 '23 at 16:09
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    @Adiyarkku Ptolemy had no accounts of a six month's darkness, but had likely heard of somewhat longer/shorter days in the north. But the tilt of the earth can explain this no matter where you put your origin of the coordinate system. The heliocentric model had no better predictive power than the geocentric; it's just a matter of transformations. The main advantage of the heliocentric model, in addition to being simpler, is that it is in accord with the law of gravity, but at the time of Ptolemy, they didn't concern themselves so much with reasons of the motion, besides the power of god(s). – pela Oct 15 '23 at 16:30
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    Okay got it @pela – Adiyarkku Oct 15 '23 at 16:48
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    The question is besides the point, because ancient peoples didn’t know that there is six months of darkness and six months of sunlight at the exact pole. They didn’t think that humans lived that far north. Even in the Almagest (and I know, as I translated it to French), Ptolemy mentions that such parts of the world are most likely uninhabited, because they are too cold (just as the regions south of the tropics were thought to be too hot). – Pierre Paquette Mar 12 '24 at 21:29
  • @Adiyarkku: One can only wonder from what travelers did Ptolemy would have learned about the 6 month thing. – Lee Mosher Mar 12 '24 at 23:45