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Sidereal

$[[Patek Philippe Sky Moon Tourbillon Ref. 5002]],\\ with (among others) display of the **sidereal time** (click to enlarge!)$
Patek Philippe Sky Moon Tourbillon Ref. 5002,
with (among others) display of the sidereal time
© Patek Philippe

Sidereal time measures the earth's movement relative to fixed stars rather than the sun.

Similar to solar time, sidereal time measures the earth's movement rather than a fixed increment of seconds. A mean sidereal day is 23 hours, 56 minutes, 4.0916 seconds, slightly shorter than a mean solar day.

Watches that measure sidereal time generally use a full sub-dial with hour and minute hands on a 24-hour scale. In contrast, solar time is generally displayed with an arrow, since it varies more or less than the calculated length of a day.

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