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intrinsicrice t1_ja9iyd9 wrote

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

How could they determine that the 21st of december is the shortest day? Luck?

Without any research, I guess that it can’t be more than a couple of minutes shorter compared to the 20 and 22 december?

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DressCritical t1_ja9npti wrote

They didn't, not always. Many cultures celebrated, not the solstice, but the day when they could tell that the day was getting longer and thus someday summer would return again.

The solstice wasn't necessarily the shortest day of the year (though it is). To these people, it was the day when the Sun at noon was lowest in the sky. That it was definitely the shortest day seemed likely given what else they knew, but they often could not measure the length of the day.

Measuring the comparative height of the Sun in the sky, however, takes a stick, the ground, something that can mark the ground, and some patience.

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KarmaticIrony t1_ja9ngu2 wrote

They didn't pick December 21st, they did the inverse in a way. The people who built it didn't use a calendar with December as a month if they had any sort of calendar at all.

What they did was use their knowledge of how daylight changes seasonally each year, which is something they could observe, to ensure that the sun would illuminate a chamber specifically during the Winter Solstice, which happens to be December 21st on our calendar.

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IrishFlukey t1_ja9jfim wrote

Simple things like lengths of shadows. The same kinds of simple things that we can do now.

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annomandaris t1_jaantsm wrote

put a stick in the ground, at noon on each day, measure the shadow, the higher the sun is in the sky, the closer to the stick the shadow will be. On the day the shadow is the farthest from the stick, that means the sun is the lowest in the sky, and that's the shortest day.

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TheSkiGeek t1_jabkzg4 wrote

Hard to tell when it’s exactly noon.

More reliable to mark where on the horizon the sun sets/rises each day. When the movement of that point stops and reverses, that’s either the winter or summer solstice.

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