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What's the name for the dial on a wristwatch or clock which rotates to display a sun symbol at midday and a moon symbol or or night scene at midnight?

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'I doubt very much that there's a dedicated name for that particular "dial". It's usually just called a Sun and Moon indicator – FumbleFingers May 14 '13 at 16:49
@FumbleFingers: Actually, I wouldn't have been surprised at all to find there was a specific name for that piece – but an obscure word, and more likely answered on Clockmakers.SE than on English.SE. :^) Still, I found it interesting to learn that some clocks have sun-and-moon dials to indicate the time of day, but others have moon dials, to indicate the phase of the moon. – J.R. May 14 '13 at 18:52
Any thing but avoid sundial & moondial because they are commonly understood to mean entirely different things. sundial: 'An instrument showing the time by the shadow of a pointer cast by the sun onto a plate marked with the hours of the day.' moondial: 'a dial used to indicate time by moonlight.' – Kris May 15 '13 at 4:47
@Kris: I agree about avoiding sundial, but I think sun dial and sundial are not the same. – J.R. May 15 '13 at 10:02
up vote 4 down vote accepted

Antiquorum-Lexico.pdf, an “Illustrated Horological Glossary”, on page 134 (pdf page 13) apparently refers to that dial like that as a “Day/night” dial.

Astronomically-related terms elsewhere in the glossary's dial section include Astrolabe, p. 133; Moon phase and Planetarium, p. 136; Star chart and Sunrise, sunset, p. 137.

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From Wikipedia : An astronomical clock is a clock with special mechanisms and dials to display astronomical information, such as the relative positions of the sun, moon, zodiacal constellations, and sometimes major planets.

So, I gess, you could call that an astronomical wristwatch or dial, as they do in the article.

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except that it's just a half-speed version of the hour hand (like a 24-hour watch), rather than knowing about the positions of planets or phase of moon (but upvote because interesting link!). – OJW May 15 '13 at 11:31

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