How can a sundial reliably work when the sun’s position in the sky changes from day to day and month to month with days getting longer/shorter, etc?
In: Technology
From an outside perspective, 24 hours is how long it takes for one point of the earth to spin around and directly face the sun again.
From an earthling’s perspective, 24 hours is how long it takes for the sun to reach the high point of its arc through the sky.
This high point is called “noon.” It happens at essentially the same time every day, whether it’s January or July.
The days get longer and shorter not because the sun is moving at different speeds or getting to its high point at different times, but because the arc it carves through the sky is getting higher and lower. In winter, more of the arc is below the horizon, so the sun is up less.
So the sun is still at the same *direction* every day at noon, just higher or lower in the sky, and so its shadow points the same direction at that time, just longer or shorter. So 11am and 1pm also cast the same shadow year round, as do 10am and 2pm, and so on. The only difference is the arc will be high enough where you’ll get a shadow at say 6am in June, but not in December, so the extremes of the sundial can indeed be useless in winter.
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