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Sidereal verge watch, c 1776.

Sidereal verge watch, c 1776.
4 0 c m
actual image size: 26cm x 32cm


Detail of dials. This verge escapement watch showing solar and sidereal time and with epicyclic maintaining power was made by James Green of London. The watch is in a silver pair case hallmarked 1776. It ndicates solar time on one set of dials and sidereal time on the other. A sidereal day is the interval of time between one pasage of a given star acros the meridian in the southern sky and the next pasage of the same star. It is nearly four minutes shorter than a solar day because the sun itself is moving slowly through the stars in a direction opposite to that of the apparent rotation of the stellar system round the earth's axis.

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© Science Museum / Science & Society Picture Library

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