ObjID182-1
‹ Ancient Sundials
Dialface ID 181
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Abstract
The museum has restored this dial by joining two halves. Eleven hour lines cross three day curves. The third, sixth, and ninth hour lines are specially marked. A simple sloping base supports the dial face.
Measurements
Measurement record: pipeline ObjID 182, matched to this dialface by inventory number.
| Quality grade | B (completeness 100 %) |
|---|---|
| Dial surface | cone (decisive) · fit residual mm: cone 0.61, cylinder 5.86, sphere 6.27 |
| Latitude φ | 30.92 ± 4.01° (consensus of witnesses) |
| Klima | Alexandria (III), Rhodes (IV), Syene (II) |
| Engraved lines | 11 hour lines, 3 day lines |
| Cone half-angle α | 32.9 ± 0.11° (cone residual on all points 0.62 mm) |
| Measured | 2026-06-12 20:32 |
What the dial shows at this latitude
| Winter solstice | Equinox | Summer solstice | |
|---|---|---|---|
| Noon altitude of the Sun | 35.4° | 59.1° | 82.8° |
| Noon shadow (gnomon heights) | 1.41 | 0.60 | 0.13 |
| Length of the day | 10.0 h | 12.0 h | 14.0 h |
| Length of a seasonal hour | 50 min | 60 min | 70 min |
Computed for the measured latitude with the obliquity of the JPL ephemeris at 101 BC (year -100). The latitude is the one the dial was made for, not a find-spot coordinate.
References
- – Gibbs, Sharon L., Greek and Roman Sundials, New Haven and London, 1976, p. 300.
- – Severino, Nicola, De Monumentis Gnomonicis apud graecos et romanos. Le meridiane greco-romane. La storia, il catalogo, gli articoli, Roccasecca, 2003, p. 46.
3D Models
