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Successful_Box_1007 t1_jaayq46 wrote

Reply to comment by Ansuz07 in Eli5: How did people know how long a year was in olden times? by Slokkkk

Cool AF! Didn’t know that they were able to track and measure they solar altitude! How did they do this with their rudimentary tools?

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redvillafranco t1_jab7ala wrote

You can just look at where on the horizon the sun rises/sets every day. On the first day of summer, the sun rises the furthest north in the northern hemisphere. So you just count the days until it rises that far in the north again.

Also, you can measure the highest point of the sun in the sky each day. If you have the same length stick or rock on the ground. On the first day of summer, at high noon, the shadow will be its shortest length of the whole year. So you can just count the days until the shadow is that short again.

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Successful_Box_1007 t1_jab7kef wrote

And the ancients just assumed this meant that the earth had made a full rotation (or in their eyes, the sun had)? I mean why did they settle on that assumption? I am sure one could have made a dozen others.

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yogert909 t1_jab8ny7 wrote

They didn’t necessarily care about the rotation of the earth. They cared about how long until they should plant their crops again.

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redvillafranco t1_jab8rba wrote

They knew that a cycle of 365 days had passed. And this period of time was extremely consistent and repeatable. And they called that cycle a “year”. But they didn’t necessarily need to know what was causing the cycle.

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AliMcGraw t1_jabaz04 wrote

There was a NOVA episode just a few weeks ago that demonstrated exactly how people could do this with very simple tools! (Like, stick in the ground simple.)

The records they were sharing and recreating were from the last 1,000 years, but it's not appreciably different from what Eratosthenes did, and what we assume older calendar-making societies did. And they demonstrated so beautifully exactly how it works, A+++ go watch the show and then plant your own stick in the ground to measure sun things!

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PlanetLandon t1_jabiddd wrote

It doesn’t really take anything special. If you have eyes and something to write with you can keep track of where the sun rises every day.

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Successful_Box_1007 t1_jabk5wa wrote

True but isn’ the variation super small all things being equal (including time of day you measure)? With their rudimentary tools it must have been tough.

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TheSkiGeek t1_jabknby wrote

Yeah, but you only need to get close. It’s okay if you’re off by a day or two if all you’re using it for is to decide when to plant and harvest crops.

If you’re staying in one place for a while you can set up more permanent solutions. Structures like Stonehenge have notches and openings that line up with the sun position in different seasons, so you can tell exactly which day is the solstice or equinox (or whatever days are important to you).

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p_m_a_t_t t1_jabkoi0 wrote

Just because a tool is 'rudimentary' doesn't mean it doesn't work!

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Mr_Mojo_Risin_83 t1_jabucot wrote

remember, there was no telly or movies or anything at this time. this sort of knowledge would have been carried by everyone in the tribe. this is the sort of thing they could have devoted time to every single day.

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