Ancient Sundials

Dialface ID 416

ObjID375-1

Holder:: Casa Rossa, Anacapri, Italy
Site:: Unknown, Unknown
Material:: Unknown
Dating:: unknown
Type:: Sphere, Spherical-cut dials--central gnomon point

Abstract

La meridiana romana di Anacapri, come si vede allingresso della Casa Rossa, incastonata nel muro insieme ad altri antichi reperti. Veduta frontale della meridiana. E ben conservata con 11 linee orarie ben incise, le due curve solstiziali e la linea equinoziale. A destra il profilo del quadrante.

Measurements

Measurement record: pipeline ObjID 375, matched to this dialface by inventory number.

Quality grade	B (completeness 93 %)
Dial surface	sphere (decisive) · fit residual mm: cone 4.12, cylinder 4.44, sphere 0.82
Latitude φ	47.33 ± 2.59° (consensus of witnesses)
Klima	Borysthenes (VII), Mid-Pontus (VI), Massalia
Engraved lines	11 hour lines, 3 day lines
Cone half-angle α	not shown: surface fit decisively sphere: cone-specific quantities do not apply
Measured	2026-06-12 20:44

What the dial shows at this latitude

	Winter solstice	Equinox	Summer solstice
Noon altitude of the Sun	19.0°	42.7°	66.4°
Noon shadow (gnomon heights)	2.91	1.08	0.44
Length of the day	8.2 h	12.0 h	15.8 h
Length of a seasonal hour	41 min	60 min	79 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. 146-148.