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The Encyclopedia of Horology

Clock type · Precision

Sidereal Clocks

Partially verified

Clocks regulated to keep sidereal time (based on the earth's rotation relative to fixed stars), used in observatories.

Movement & mechanism

  • Gear train calculated to run at the sidereal rate (approx. 3m 56s faster per day than solar time)
  • Often have a 24-hour dial
  • Precision regulator-grade movements

Identification

  • 24-hour dial starting at 0 (or 24)
  • Observatory provenance or labeling
  • Extremely fine finish and deadbeat escapement

Terminology

  • Sidereal time
  • Observatory regulator
  • 24-hour dial

Known variations

  • Wall and floor-standing regulators

Collecting notes

Condition and originality are paramount. For technical clocks like regulators or atmospheric clocks, the completeness of the original mechanism is more important than case condition. For decorative clocks (Boulle, Empire), the quality of the case craft is central.

Related photographs

The Prague Astronomical Clock in Old Town - 8559
The Prague Astronomical Clock in Old Town - 8559 — Jorge Royan, CC BY-SA 3.0. Wikimedia Commons file page
Czech-2013-Prague-Astronomical clock face
Czech-2013-Prague-Astronomical clock face — Godot13, CC BY-SA 4.0. Wikimedia Commons file page

No confidently matched photograph of this subject has been found yet. These photographs show a closely related record, and are not examples of the type described on this page.

Sources & references

  1. Britten, F. J., Old Clocks and Watches and Their Makers
  2. Loomes, B., The Early Clockmakers of Great Britain
  3. Roberts, D., British Skeleton Clocks
  4. Museum catalogue records

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