A meridiana is a sort of solar observatory, where a small hole in the roof of a large dark building projects a pin-hole image of the Sun that crosses a N-S line on the floor at noon. The crossing point along the line varies with the season. They are most commonly found in Italy and I was recently lucky enough to visit three in sunny equinoctial weather.

The meridiana in Rome is in  Santa Maria degli Angeli e dei Martiri, a makeover by Michelangelo of the central hall of Diocletian’s Baths. Francesco Bianchini was commissioned by Pope Clement XI to instal  the 44m long line with its foro gnomico 20m above in 1702. The aims were to check the Gregorian calendar introduced in 1582, to aid in the determination of the correct date for Easter, and presumably to check on the measurements made by Giovanni Domenico Cassini in San Petronio in Bologna in the 1660s using a similar instrument.

Cassini had measured the apparent diameter of the Sun through the seasons and found that the data better fitted Kepler’s theory of elliptical orbits than the theories of Ptolemy accepted by the Church as consistent with dogma. It later served as the time standard for Rome up til 1864.

The brass line is set into the marble floor with arcane inscriptions and coloured marble representations of the signs of the zodiac appropriate for each time of year. It was restored in AD2000 and looks splendid.

We joined a small band of enthusiasts watching the trembling disc of light creep towards and over the line at near 1PM European time.




The meridiana in Naples is not in a church but rather in the Gran Salone della Meridiana in the National Archeological Museum.

It shares the room with a marble statue of Atlas holding a globe. It looks a bit over-the-top but is worth a second look. It is the celebrated ‘Farnese Atlas’, named for a one-time owner, and is believed to be a second century AD Roman copy of an earlier Greek statue, and the globe is a celestial globe, with the oldest known representation of the constellations recognised by Ptolemy.

The meridiana was installed in the 1790s when it was planned to be part of an astronomical observatory. There is a brass strip set in marble panels with paintings of the signs of the zodiac set behind glass at the appropriate points along the 27 metres.  There were only three other viewers, exchanging questions and answers in four languages.





A week later I was able to visit Palermo Cathedral. The meridian there  is 22m long, installed by Father Giuseppe Piazzi in 1801. Its purpose was to help coordinate the time in Sicily with the rest of Europe. Little notice was being taken of it, and even I moved on to find some lunch before the bright disc crossed the line.