Science · 6 pages · 12 min

Why a sundial is not a clock you can trust all year

A sundial follows the uneven true Sun, while clocks follow a smoothed average Sun.

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From the opening

A sundial is not a year-round match for a clock because it reads the true Sun, whose noon-to-noon pace is uneven, while civil clocks follow mean solar time. The difference between those two times is the equation of time, and it grows and shrinks in a pattern that returns each year. The opening covers ellipse and tilt as two causes, what the equation of time corrects, and what the analemma draws.

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Inside

Ellipse and tilt as two causes
What the equation of time corrects
What the analemma draws
What a time zone adds
Where the idea stops applying
A distinction worth keeping

Sources

The equation of time
Apparent solar time versus mean solar time

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Why a sundial is not a clock you can trust all year

From the opening

Inside

Sources

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