Hello Big John,

One thing if for sure, when the Egyptians build their first Pyramids, around 3500 BC, they already new the exact position of the equinox in a way that even today we would have difficulty to build a so huge construction that is perfectly aligned with the True East and West line as the pyramids are.

On the equinox day the sun sets on the true West and the sun rises on the True East. Drawing a line from those two points at that time of the year gives a good idea of the direction for the true East/West line. Finding the place where the sun sets on the Equinox in those times is the only way I know of to find that line. Yet the finding with such precision the angle of that line in the way the pyramids where build would be a challenge for any surveyor and builders of today with all the tools we have.

As for realising that the time of day = the times of the night on the equinox day. Don't know how they did it, and when we realized it was such a thing on the equinox day.

The oldest sun clock dates from around 1500 BC. But then it only gives the time during the daylight. How did they calculate the time during the night time to compare with day time? Most probably from observation of the movement of the stars. But this is only speculation from my part.

Even more fascinating than the equinox, is the knowledge they had in those times, as shows for example the Mayan calender, of the north/sud pole axis of rotation of the earth doing a precessional circle in the sky that takes 25 920 years. It's from this movement of the axe of rotation of the planet that we say that we are entering the age of Aquarius that will last for about 2160 years.

Have a great day!