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During the day, the sky is bright blue and, along with the yellow light from the Sun, it illuminates the surface of the Earth.

What is the earliest recorded knowledge that the sky wasn't self-illuminating, but simply something that was itself illuminated by the Sun?

Ray Butterworth
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    I think only modern people, who spend a lot of time indoors and with artificial lights, are able to not know that. Anyone else should have noticed that the sky gets bright when the sun rises, and dark when the sun sets. Also, at those times it's visibly darker on the site opposite the sun. That's not rocket science. – Torsten Schoeneberg Jan 26 '23 at 03:23
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    @TorstenSchoeneberg Alternatively, they could believe that when it grows bright, the sun rises, and when it grows dark, the sun sets. I have read a tale in which the gods intend to make a brother the sun and a sister the moon, and she insists on reversing it because it's not proper for women to go out at night, and then she shines very brightly so people will not stare at her, because she's properly modest. That would make the day first and the sun after. – Mary Jan 27 '23 at 00:38
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    @Mary Nice tale, what is its source? Anyway, I stand by my claim that if one actually watches a sunset or a sunrise, it becomes quite clear what illuminates what. – Torsten Schoeneberg Jan 28 '23 at 16:46
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    @TorstenSchoeneberg In the Book of Genesis, day and night are created on the first day, but the sun and the moon are created only on the fourth day, as objects to rule the day and the night. Also, living in a coastal climate, I am used to heavily overcast days (like today) when no trace of the sun is visible. It is still light outdoors, and the source of light is not immediately obvious. – Per Manne Jan 30 '23 at 14:19
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    Well I'm a person, and I knew it in 1965, so we know it's before that at least :-) – uhoh Jan 30 '23 at 22:00
  • The Ancient Egyptians at least knew this. It was a major part of their worldview. – Spencer Jan 31 '23 at 14:17
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    @Spencer, if you have a reference for the Ancient Egyptians, it would make a good answer. – Ray Butterworth Jan 31 '23 at 17:14
  • Interestingly, the Mesopotamians had separate gods for the sun and for daylight. – nwr Feb 01 '23 at 19:18
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    @TorstenSchoeneberg, I agree with your theory. Additionally to what you have said, for so long as humanity has known fire, it has known the concept of both illumination and of radiant heat, and of shadowing. Whilst the exact mechanics of the heavens may not have been known, the inference that the sun was providing the source of both daytime warmth and light in a manner comparable to a fire, is not a significant leap. To argue that the sky was "self-illuminating", was probably never a widespread belief, since the sun is always co-present with the illumination and sufficiently explains it. – Steve Feb 04 '23 at 15:28
  • @nwr: I think that is an imprecise account. Just from reading the Wikipedia articles linked from there, there is a Mesopotamian / Akkadian sun god, and his wife, the goddess of dawn. They come together in the morning and re-unite in the evening. The concept of "dawn" seems significantly different from the concept of daylight. – Torsten Schoeneberg Feb 05 '23 at 23:10

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