Case Study 11.
3: Strasbourg Cathedral, France,
and Astronomical Time
Presentation and analysis of the site
Geographical position: City of Strasbourg, Département du Bas-Rhin, Alsace region, France.
Location: Latitude 48º 34´ 55˝ N, longitude 7º 45´ 5˝ E. Elevation 150m above mean sea level.
General description: The Cathedral of Notre Dame, constructed from the 11th to the 14th
centuries, forms the core of this site. Several original timekeepers which have been removed
from the cathedral are now in Strasbourg’s Museum of Decorative Arts and Musée de
l’Œuvre Notre-Dame. The Cathedral forms part of the World Heritage property ‘Strasbourg–
Grande Île’ inscribed on the List in 1988 under criteria (i), (ii) and (iv).
Inventory of the remains related to astronomy:
Location Description
Sundials
Niche in buttress of south transept; original Statue of youth with a sundial (1225 × 1235)
in Musée de l’Œuvre Notre-Dame
Gable of south transept Three vertical sundials, Conrad Dasypodius (1572)
Exterior wall of the Treasury Vertical sundial (1488?)
Exterior buttress of the Treasury Vertical sundial (15th century)
South transept above clock; original in Relief of astrologer with a sundial (c. 1490)
Musée de l’Œuvre Notre-Dame
Inside door of south transept Meridian line (1838–42)
Tower’s four sides at platform level Four vertical dials (16th century)
Tower’s south side at platform level Meridian with triangular stylus and single vertical noon line
(16th century)
Tower Statue of man holding sundial-like shield with concentric
circles (late 15th century)
Clocks
South transept, above entrance External clock shows hour of day and day of week (and
corresponding planet)
Formerly opposite the present clock in the First astronomical clock (1352–4)
South Transept; cock-automaton in Museum
of Decorative Arts
Formerly in the location of the present clock Second astronomical clock (1571–4), Conrad Dasypodius
in the south transept; mechanism now in
Museum of Decorative Arts
In the south transept Third astronomical clock (1838–42), Jean-Baptiste Schwilgué
Zodiac
West front, right portal, niches in bases of Zodiac and occupations of the months (late 13th-early 14th
statues centuries)
Medieval astronomy in Europe 185
History of the site: With the construction of the west front, the cathedral obtained its earliest
known display of astronomical time—one that the cathedral shares with many other large
churches—the carved reliefs depicting the signs of the zodiac and the labours of the months in
the bases of the statues flanking the right portal (Fig. 11.3.1).
The most widely known of these astronomical displays of are the cathedral’s elaborate
astronomical clocks. The 14th-century clock included a calendar, a mechanically driven
stereographic projection showing the movement of the stars, and pointers showing the
positions of the Sun and Moon. Atop the clock was an automaton of a cockerel, which crowed
at noon, flapping its wings.
The 16th-century clock added to these elements a rotating celestial sphere on which were
depicted all 1020 stars of Ptolemy’s star catalogue together with figures of 48 constellations,
a disc showing the ecclesiastical calendar for 100 years, and depictions of all eclipses over an
interval of 32 years. A stereographic projection of the stars, Sun and Moon, like the one in
the original clock, was enhanced with additional pointers showing the positions of all the
visible planets and the ‘Dragon’, or lunar node, which served to explain eclipses (Fig.
11.3.2a). Elements of the case and display were incorporated into the current clock. Although
the clock reflected the geocentric model of astronomy, its decoration included a portrait of
Nicolas Copernicus.
The 19th-century clock reflected Copernican astronomical concepts. The geocentric
stereographic projection of the Sun, Moon, and planets was replaced by a heliocentric model
of the visible planets, plus the Earth and Moon, in the solar system (Fig. 11.3.2b). It displayed
both uniform civil time and the apparent time indicated by the daily motions of the Sun. The
stellar globe now portrayed more than 5000 stars, extending down to faint sixth magnitude
ones. In addition, the clock incorporated a perpetual calendar, computing the ‘solar’ cycle of
28 years, the lunar cycle of 19 years, the date of Easter, and other calendrical parameters
traditionally found in ecclesiastical computus.
The concern with time that we see in the cathedral’s clocks also appears in its fourteen
sundials, which date from the 13th to the 18th centuries. The oldest sundial, dated between
1225 and 1235, marks seven times of prayer in the course of the day, beginning at dawn and
continuing until sunset. The 15th century saw the addition of three more sundials, dividing the
day into twelve hours from sunrise to sunset (Fig. 11.3.2c). In the 16th century, five dials
were installed at the platform level of the tower and three mathematical dials, designed by the
builder of the second clock, were installed on the gable of the south transept (Fig. 11.3.2d).
The builder of the 19th-century clock, Jean-Baptiste Schwilgué, installed a vertical meridian
line inside the entrance to the south transept (Fig. 11.3.3), marking local apparent noon to
regulate the clock.
Fig. 11.3.1. Occupations of the months and signs of the zodiac, west façade, right portal—May, Gem-
ini; June, Cancer; July, Leo; August, Virgo. Photograph © Ad Meskens, Creative Commons Licence
186 ICOMOS–IAU Thematic Study on Astronomical Heritage
Fig. 11.3.2. Top left (a): Astrolabe planetary dial of the second astronomical clock. Detail from
Woodcut by Tobias Stimmer (1574). Top right (b): Heliocentric planetary dial of the third astronom-
ical clock. Photograph © Didier B (Sam67fr), Creative Commons Licence. Bottom left (c): Astrol-
oger with a sundial, south portal. Photograph © Coyau, Creative Commons Licence. Bottom right (d):
Three sundials on south gable: altitude/azimuth dial (left), vertical sundial (centre), and dial reading
hours from sunrise and sunset (right). Photograph © Jean-Marie Poncelet, Creative Commons Licence.
Cultural and symbolic dimension: The display of astronomical time was central to the cultural
uses of astronomy in medieval Europe. Strasbourg cathedral, which was the ‘principal
element of the nomination’ for the World Heritage Site Strasbourg–Grande Île, embodies
these astronomical concepts in three ways. Symbolically, the cathedral’s sculptures bind the
zodiac to the labours of the months; at a more direct practical level the cathedral displays
astronomical time in numerous sundials; and—perhaps most famously—there is the historical
sequence of its three great astronomical clocks.
Notwithstanding this, the description of the attributes of value of the property—both in the
‘justification of value’ from the State Party and in the ICOMOS evaluation—takes a classical
heritage approach, elucidating this exceptional Gothic church in terms of the history of art, the
history of structural design, the history of urban construction, and the history of medieval
Christianity, but does not elaborate at all on the astronomical features of the place.
Medieval astronomy in Europe 187
Authenticity and integrity: The Cathedral clocks have undergone successive transformations
through the centuries; the present 19th-century clock is a development in the tradition of the
14th-century original. Much of the cathedral’s statuary, including two of the sundials, have
been replaced by copies; the originals are preserved in the Musée de l’Œuvre Notre-Dame.
Present site management
Present use: The cathedral is a place of worship
and also a centre of tourism.
Protection: The Cathedral was designated a
Monument Historique in 1862 and has been part
of a World Heritage Site since 1988.
State of conservation: The astronomical elements
of the cathedral are involved in the general
conservation management plan of the building.
The present state of conservation of these
elements is good.
Context and environment: The Cathedral is
located in a historical, urban environment.
Main threats or potential threats to the sites:
Pressures of development and tourism.
Management, interpretation and outreach: The
Cathedral provides tours of its major sites,
including the clocks and the platform at the tower Fig. 11.3.3. Schwilligué’s meridian line
where some of the more important sundials are (detail), inside entrance, south transept.
located. The Museums have an active program of Photograph © Jean-Marie Poncelet, Creative
interpretation of their collections. Commons Licence
Additional bibliography
Oestmann, Günther (1993). Die astronomische Uhr des Straßburger Münsters: Funktion und
Bedeutung eines Kosmos-Modells des 16. Jahrhunderts. Stuttgart: Verlag für Geschichte
der Naturwissenschaften und der Technik.
Poulle, Emmanuel (1983). “L’horloge planétaire de la Cathédrale de Strasbourg”, Journal for
the History of Astronomy 14, 33–46.
Schwiligué, Charles (1844). Description abrégée de l’Horloge astronomique de la Cathédrale
de Strasbourg. Strasbourg: Imprimerie Dannbach.
