They knew one obelisk did not cast a shadow at a certain date (the solstice) so, on that date
Surely it's also about the time of day, not just the date? You need to compare shadow lengths at the same time on the same date. How could they accurately measure time back then?
I'm guessing they measured the shadow when it was shortest.
On the southern obelisk the sun was directly overhead so they measured no shadow at its shortest.
On the northern obelisk they measured the shadow at its shortest which had to be at the same time the other obelisk had no shadow. So no need to synchronize clocks. Just measure the shadow at its shortest which must be at the same time for both.
Pretty shitty attitude to lash out at someone asking legitimate questions. This is how people learn. It sucks that if they were to take you seriously, they would be discouraged from asking questions the next time around. Just pretending like they understand when they don't.
I am most certainly not a flat-earther, but I also was curious how they managed to ensure that they measured at the same time. They did not have watches, maybe they had sun-dials (if they did, would they be accurate enough? They are based on shadows, obviously)?
The answer is not obvious; and as expected, the people back then were clearly pretty smart to come up with it.
I'm happy understanding more clearly how the experiment was conducted. And if I ever run into a flat-earth loon, and they ask the same questions I had, I'll have the answer ready for them... And then they'll deflect and probably go on about some ancient Egyptian conspiracy, or just ignore me and start talking about the ice wall.
You measure the shadow when the sun its at its peak. Since both places are (roughly) on the same longitudinal line (i.e Alexandria is to the north of Syene), it will happen at (roughly) the same moment of the day.
or, as the other commenter said, you measure when the shadow is at its shortest (which is another way of saying you measure when the sun its at its peak, for places that are on the same longitude)
the method is very dependent on the two cities being on the same longitude. if the cities were Ecuador and Alexandria, the measured angle would be the same, but the distance is much greater.
You are a scholar in alexandria and always walk by this nice obelisk and maybe even sit down in it‘s shade to relax for a while. You read in a book, that there is another obelisk wich doesn’t cast a shadow ob a specific date. It strikes you as odd, because you can’t remember your obelisk not casting a shadow. So you set out on that day to look at your obelisk and there it is: a long shadow. You must find out why that is.
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u/ilikepix Nov 11 '23
Surely it's also about the time of day, not just the date? You need to compare shadow lengths at the same time on the same date. How could they accurately measure time back then?