MONUMENTAL SUNDIAL . MUSEO GALILEO . FLORENCE

Lizard / Viper Gnomon of Monumental Dial . Museo Galileo . Florence

MONUMENTAL SUNDIAL . MUSEO GALILEO . FLORENCE

The Museo Galileo‘s Monumental Sundial was built as a mathematical ornament in 2007. The slender bronze column (stele) is in fact formed from two matching columns closely aligned, symbolising day and night. The (mid)day stele faces south, with a vertical meridian line on which the shadow is cast by a lizard’s tail (actually, an imaginary half-lizard, half-viper). The night stele faces north and signifies the constellations Ursa Major and Ursa Minor that enable the Pole Star to be identified.

Monumental Dial . Museo Galileo . Florence

The encircled quadrant design on the pavement at the base of the bronze columns indicates the geographic orientation. This glass base of the gnomon, and also the Zodiac signs in the meridian line (below), are up-lit after dark.

Orientation dial . Monumental Dial . Museo Galileo . Florence

The Museo explains the meridian line in helpfully simple terms: A travertine and brass meridian line is drawn on the pavement, flanked with glass and marble signs of the Zodiac. The meridian line extends for about 15 metres from the museum entrance, where the winter solstice is marked, to the base of the gnomon, where the summer solstice is marked. The travertine curves crossing the meridian line indicate the date. The brass radial lines forming a grid with the two solstitial curves indicate the hours.

The seasons and the four elements are symbolised by the choice of materials: travertine for the earth and autumn; glass for the water and winter; grey stone for the air and spring; bronze for the fire and summer.

LIZARD / VIPER GNOMON ON THE SOUTH FACE OF THE COLUMN

This extraordinary sundial stands by the Arno with the Ponte Vecchio (which itself has a wonderful dial LINK) close by to the west. For anyone with even a minuscule interest in or curiosity about the gradual development of scientific instruments and techniques from medieval times onwards, pay a visit to the excellent online gallery LINK. Look in particular for the two astronomical telescopes made by Galileo himself.

The North American Sundial Society has very good online information about this unique dial. You can watch a short animation of how this gnomonic sundial works here LINK

For those interested in finer details of the way the dial works, the museum’s detailed account is included at the end of this article.

Museo Galileo – Istituto e Museo di Storia della Scienza

Museo Galileo – Monumental Sundial

NASS (North American Sundial Society) Video: Filippo Camerota, Luise Schnabel, Giorgio Strano

How the Sundial works

The shadow cast by the glass polyhedron atop the large bronze gnomon indicates the date and time. The hours from 9:00 AM to 2:00 PM are marked out by radial brass lines. The date is indicated by the travertine traversal lines which mark the Sun’s diurnal course for various periods of the year – precisely when the Star enters the signs of the Zodiac. The shadow cast by the gnomon changes in length during the course of the days and seasons, and indicates true solar time for the place where it is located, which is a different time than that of our wristwatches, known as mean time. In respect to mean timetrue solar time has a periodic variation that can exceed a quarter of an hour.

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Moreover, during daylight saving time, the hands of a clock are moved forward one hour. For example, true midday in the month of February would be indicated by the sundial around 12:28 AM while in the month of July it would be indicated around 1:20 PM daylight saving time.

To read the hour and date, you have to identify the hour lines and the calendrical lines closest to the gnomon’s shadow. When the shadow does not fall exactly on a hour line, you can read the half-hours and quarters with close approximation by ideally subdividing the space between two hour lines in two or four parts. The date can also be read by referring to the Zodiac signs and the start of the months marked out along the meridian line.

© 2018 – 2022 Museo Galileo – Istituto e Museo di Storia della Scienza
Piazza dei Giudici 1 · 50122 Firenze · ITALIA
tel. +39 055 265 311 – P.I. 01346820481

PONTE VECCHIO . FLORENCE – ‘ UNEXPECTED TIMES’: A C14 SUNDIAL

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‘ UNEXPECTED TIMES’: A SUNDIAL ON THE PONTE VECCHIO

This article was written a while back, in the pre-Covid era. Now I have a sundial site up and running, this dial and some others from Florence have a new space.

Florence in January.  -8°C at night, zero during the day – but sunny enough in the middle of the day to be able to have coffee or even lunch outside. Apart from the Uffizi, no queues for anywhere. Most significant places on the tourist trail almost to oneself. Despite the cold, there is no frost: the air is so dry that the pavements, piazzas and even the cars are quite clear of frozen white crystals. By the river I caught the electric flash of a male kingfisher flying up from the water to an overhanging bush, his hunting perch. I watched him as he scanned the water below, occasionally diving down and returning to the same branch. Twice, I could see the glint of a tiny fish in his beak. 

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Over the years I don’t know how often I have crossed the Ponte Vecchio – or even simply walked to the mid-point to admire the views up and down river from the open areas between the pricey shops. This time I was walking the length of the Vasari corridor that connects the Palazzo Vecchio to the Palazzo Pitti on the other side of the Arno. A section runs straight over the bridge and then passes across the facade of Santa Felicita, into which the Medici family could sneak from the corridor to a large private balcony for spiritual refreshment. Passing the middle of the west side of the bridge, in the ‘tourist photo op’ gap where Cellini’s bust adds to the photogenic view, I have never before looked upwards.

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Here, on the roof of a shop, is an ancient sundial, supported by a white marble pillar. An eroded and almost illegible engraving below the pillar records that in 1333, floods caused the bridge to collapse and that “twelve years later, as pleased the Commune, it was rebuilt with this ornamentation”. The sundial itself, with its columnar divisions reminiscent of a rose window, marks the CANONICAL HOURS. The gnomon’s shadow indicates the hour of the day. If the sundial is the ‘ornamentation’ to which the inscription refers, then it is around 650 years old.

If you look closely, you’ll see, halfway up the south face of the hexagonal column, a lizardsundial-ponte-vecchio-florence-1

Seeing the sundial for the first time ever, yet in such a familiar place was a reminder that Florence is a city that demands great attention as one walks through the streets. Many buildings, even unassuming ones, have fine adornments high up that will catch the eye… but only if you are looking out for them. 

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