Ancient Sundials

Dialface ID 358

ObjID316-1

Holder:: Museo Nazionale Romano, Rome, Italy
Site:: Unknown, Unknown
Material:: Sandstone
Dating:: unknown
Type:: Sphere, Spherical-cut dials--central gnomon point
Inventory Number:: 538381

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Abstract

Manca buona parte del quarto di sfera sinistra. Presenti 7 linee orarie dalla Prima alla Settima e le tre curve di declinazione. Manca una scheda e qualsiasi descrizione. Ignota la provenienza. Ritrovamento casuale nei depositi da parte della consegnataria Panatta.

Measurements

Measurement record: pipeline ObjID 316, matched to this dialface by inventory number.

Quality grade	C (completeness 95 %)
Dial surface	cone (preferred, not decisive) · fit residual mm: cone 1.41, cylinder 1.41, sphere 3.01
Latitude φ	36.97 ± 0.60° (single witness: path-III-front-back)
Engraved lines	7 hour lines, 3 day lines
Cone half-angle α	5.1 ± 0.34° (cone residual on all points 1.49 mm)
Measured	2026-06-12 20:43

What the dial shows at this latitude

	Winter solstice	Equinox	Summer solstice
Noon altitude of the Sun	29.3°	53.0°	76.7°
Noon shadow (gnomon heights)	1.78	0.75	0.24
Length of the day	9.4 h	12.0 h	14.6 h
Length of a seasonal hour	47 min	60 min	73 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.

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References

– Severino, Nicola, De Monumentis Gnomonicis apud graecos et romanos. Le meridiane greco-romane. La storia, il catalogo, gli articoli, Roccasecca, 2003, p. 48.