[Hannah LS (OP)]

Jane asks:

I have been wondering how ancient peoples would know that a SPECIFIC day was the shortest day of the year (or the longest day of the year, for that matter).

It is easy enough to see that in the northern hemisphere December the 12th has much less daylight than June 12th, for instance.

But without a time keeping mechanism, how would you know that December 12th was shorter than December 11th and longer than December 13th? And how would you particularly mark December 21st (or 20th) as the shortest day?

What do you think?

[alancalverd]

Put a stick in the ground and trace its shadow. Shortest day has the longest shadow. Build a stone structure aligned with the longest or shortest shadow, or the most easterly or westerly appearance of the rising sun, and refine your alignment over a few years by chipping bits off the stones.

This explains all the henges, pyramids, etc. Nothing to do with religion, but agriculture and trade. Once you have found the direction of the rising sun at the solstices, it makes sense to build a public structure that marks the solstice precisely. Then everyone knows when to start planting, fishing for herring, or setting out on a long journey to trade. If I have Scottish leather or wool to sell to a merchant in Birmingham and it takes 20 days to get there, it makes sense to arrive at the time that someone else is bringing gold or spices up from the south coast (10 day journey), hence trade fairs, on the one hand, and the need for  accurate public calendars on the other.

It comes as no surprise that henges and tombs in the Orkneys are aligned to the same astronomical phenomena as Stonehenge, and the discovery of vast quantities of pig bones at Stonehenge simply underlines the fact that Travelodge and Premier Inn were accommodating businessmen 6000 years ago. Likewise trepanned skulls, sawn human limb bones, and "ritual human sacrifices"  around so-called "sacred" sites: once you have established a trading hub with a calendar, it seems reasonable to announce that a travelling professional such as the surgeon will be in residence during the second moon after the solstice, and the judge and executioner will arrive at the third moon. Plus ca change, plus c'est la meme chose.

[Bored chemist]

Keep a note of the position of the Sun at Sunrise (or set).
Over the year it moves East or West.
There's a day when it stops moving one way + moves the other.
That's the day  when the Sun stops and that's the "solstice".

No clock required.