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The Encyclopedia of Horology

Complication · Calendar & astronomy

Star Chart Display

Partially verified

A rotating chart showing the visible night sky for a given latitude.

Definition

A rotating chart showing the visible night sky for a given latitude.

Historical origin

An astronomical display revived in modern watchmaking, descended from astrolabe and celestial-globe traditions.

How it works

A transparent or pierced disc carrying star positions rotates at the sidereal rate behind a mask representing the visible horizon for one latitude.

Because the mask is latitude-specific, a given watch is only correct for the latitude it was made for.

Pocket watch context

Related to astronomical pocket watches and pocket celestial instruments.

Wristwatch context

A decorative and educational modern complication.

Identification

  • A star field disc with a horizon mask
  • A stated latitude on the dial or in documentation

Servicing notes

This is specialist work. Levers, springs and cam profiles in complicated work are calibre-specific, and incorrect reassembly commonly damages parts that cannot be bought. Refer the movement to a watchmaker experienced with this mechanism.

General guidance only. Complicated mechanisms should be assessed and serviced by a qualified watchmaker or clockmaker specialist, not adjusted at home.

Diagram

date ring, thirty-one positionsdate aperturedriving wheel and jumper
Schematic: calendar work under the dial. An outline schematic drawn to show the arrangement of the parts discussed here. It is not a dimensioned working drawing and does not depict a particular maker's calibre.

Sources & references

  1. de Carle, D., Watch and Clock Encyclopedia
  2. Britten, F. J., Old Clocks and Watches and Their Makers
  3. Horological Journal (British Horological Institute), technical articles

Where sources disagree, the disagreement is stated rather than resolved silently.