Temporal Hours
Temporal Hours were used in the Medieval Age when the Natural Night was divided into
12 equal parts:
Examples:
•Short Temporal Hours (< 60’) in Summer
•Long Temporal Hours (> 90’) in Winter
•Temporal Hours = 60’ during Equinoxes
Temporal (or Apparent) Hours were used in the Medieval Age when clocks and watches were not widely available and when, for practical reasoons, the Natural Night and the Natural Day were equally divided into 12 equal parts. Since a night in winter lasts much longer than a night in summer, the night hour in winter lasted longer than 60 minutes and shorter than 60 minutes in summer. Only during Equinox (in March and October), when day and night are equally long, the Temporal Hours last exactly 60 minutes.
Temporal Hours were only abandoned after accurate mechanical clocks became commonly available.
The Ulysse Nardin Astrolabium shows Temporal Hours only for the night, because the dial would otherwise be too cluttered.