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It all began with astrology.
blaisepascal

When you look up at the night sky these days, you see a smattering of stars, but before the advent of large-scale artificial lighting most people looking up at the sky would see a vast collection of stars. The "Milky Way" really did look like a splash of pale cream across the sky. Although the pattern of the stars is random, it is fixed. Night after night after night folks looking at the sky would see the same patterns and came to know them very well.

One thing that's easy to tell from a years observation is that there is a complete globe of stars in the sky, but that we can only see half each night due to the sun. Each morning the stars fade out with the rising sun and fade in each night at sun set. Each night when the sun sets, a regular progression of stars are visible on the eastern horizon. Although each night only some stars are visible, and each night a different set are visible, the pattern is continuous, and repeats each year.

That the pattern repeats each year was very important in Egypt, because by coincidence the annual flooding of the Nile (an extremely important occasion in Egypt) happened very shortly after when Sirius, the brightest star in the sky, rose at sunset. The rising of Sirius was an important predictor and watched-for event Egypt.

I suppose that the annual rising of Sirius as a herald of the annual flooding of the Nile helped cause people to regard the stars, in general, as portents of significant events upon the Earth. Studying the stars, and relating them to events on Earth, became an important profession.

The pattern of the stars wasn't 100% constant. Amongst the thousands of lights in the sky, nine of them weren't fixed in the pattern; they "wandered". The Greeks called them πλανετες -- "planets". One was the Sun, which moved uniformly against the background of the stars and blotted out in its brightness all the stars near it. Another was the Moon, which moved uniformly against the stars (but at a different speed than the Sun), was as large as the Sun, and changed shape regularly. Two appeared only in the East, rising shortly before sunrise, and two appeared only in the West, setting shortly after sunset. These four came and went, sometimes being in the sky, sometimes not appearing. The remaining three moved across the entirety of the backdrop of stars and weren't limited to just being seen at sunrise and sunset.

It didn't take long for people to notice somethings about the two morning stars and two evening stars. One of the morning stars never got more than 30 degrees from the Sun, wasn't visible in the sky for that many mornings in a row, and reappeared every 115 days or so. One of the evening stars never got more than 30 degrees from the Sun, wasn't visible in the sky for that many evenings in a row, and reappeared every 115 days or so. And there were never any days which had both this morning star and evening star visible at the same time. Obviously, these two stars were really one, one which moved back and forth across the Sun and wasn't visible when it was too close to the Sun for the same reason no stars too close to the Sun were visible -- the Sun overwhelmed them with its brightness. We now know this "star" as the planet Mercury.

Similarly, the other evening star/morning star pair were never visible on the same day, had a common reappearance period of 584 days, and both had the same maximum "elongation" from the Sun, around 45 degrees. People quickly realized that these were also one planet that moved back and forth across the Sun. Today we call it Venus.

People noticed the planets moving across the sky. They noticed that the movement of the Sun across the stars was related to the seasons. They noticed that the movement of the Moon across the sky, including its phase, was related to the rise and fall of the tides. They noticed that during the Full Moon approximately twice a year the Moon would get inexplicably dimmer, sometimes turning a deep red. The noticed that, occasionally, during the New Moon the Sun would have a chunk taken out of it as if something approximately moon-sized moved in front of it and the skies would dim. They noticed that the movement of the other five planets was irregular and not uniform. They also noticed that their fortunes were irregular and not uniform, except as dictated by the turning of the seasons (predictable by the Sun) and the rise and fall of the tides (predictable by the moon).

Humans are good at many things. Noticing patterns is one of them. Humans are very good at noticing patterns, so good we are also good at noticing patterns which aren't there. We are also subject to what is now known as "confirmation bias" -- we remember things which reinforce our beliefs and forget things which don't. EMTs find the busy nights with full moons memorable because of the bright moon out all night. They don't remember the busy nights with quarter moons as much. Ask them later if full moon nights are especially busy, and they'll go "yeah, they are". This is why scientists are careful about recording data and checking statistics. Later analysis helps eliminate supposed patterns which aren't there -- such as full moons being exceptionally busy in the ER.

So people noticed the planets moving irregularly, and their lives were irregular. They made the connection: the movement of the planets was correlated to their lives.

At one point, someone said "Hey, if the movement of the planets is correlated to our fortunes, then if we can predict the movement of the planets, then we can predict our fortunes!". And thus, astromancyastrology was born.

It turns out that predicting the movement of the planets is somewhat tricky....(continued in a future post, if I get favorable replies).

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