Although time and its measurement is a fundamental component of human life, a special type of clock which takes matters to the next level is the so-called astronomical clock and whose purpose is not to measure time per se but to convey astronomical information and, in particular, the relative position of the Sun and Moon as well as the zodiacal constellations and, in some cases, the position of the planets all as a function of time.

The oldest such effort to effectively emulate the overhead celestial sphere (ie a mini-planetarium) is the Antikythera Mechanism which was discovered in 1901 totally by accident by sponge divers off the coast of the Greek island of Antikythera. It has been dated to approximately 80 BC and it is believed to be the work of Poseidonius of Rhodes. The Antikythera Mechanism is currently on display at the National Archaeological Museum in Athens, Greece.

Note: The astrolabe is yet another instrument constructed to describe the overhead sky and monitor time. Some versions also have religious implications such as the Muslim Qibla where a magnetic compass on the back side of the astrolabe helps the user identify the proper orientation so as to point at the holy city of Mecca for prayer. Astrolabes were first developed by the Greeks around the second century BC and were slowly adopted throughout the known world of the time by numerous cultures. Astrolabes describe the position of the planets and prominent stars visible at a particular latitude (see curved markings on each dial in the photo below) and, by extension, act as time-keeping devices. Similarly, they assist in the time of expected sunrise which is vital for the Muslim religion and the timing of morning prayers at dawn ("fajr") and thereafter at noon ("dhuhr"), afternoon ("asr"), sunset ("maghrib") and nightfall ("isha"). As a result, it is no surprise that the overwhelming number of astrolabes found in museums around the world are islamic in origin given the adoption of these instruments from around 700 AD and thereafter by the Islamic World. Today's planispheres can be said to be a direct extension of the ancient astrolabe, for they function and inform the user of precisely the same information sought-after by users many centuries ago.

The brass astrolabe below is one of two astrolabes available at the Societa Ligure di Storia Patria. The astrolabe is approximately 180 mm in diameter and is both unsigned and undated. It has been cited passively by Remondini in 1878 who described it as a latin astrolabe from 1543 AD. Inspection of the mater and rete certainlly suggest a latin nature due to the (latin) inscriptions and the two I-XII hourly demarcations on the perimeter of the mater. The rete is characterized with approximately 25 star pointers and which is typical for an astrolabe of this physical size. The rule is single-armed. The astrolabe is accompanied by at least one latitude plate, thus making the astrolabe planespheric in nature, for it projects the three-dimensional celestial sphere onto a two-dimensional plane comprise of a single disk. During the Middle Ages, three-dimensional astrolabes were first described but only one such example seems to have survived to present day and which can be found at the History of Science Museum in Oxford, England (travel and photography forthcoming).

The city of Genoa is host to two museums which have at least one astrolabe in their collections, namely the Galata Museo del Mare (Galata Sea Museum) with one astrolabe and the Societa Ligure di Storia Patria (Ligurian Society of Patriotic History) where two astrolabes are available. The Societa Ligure di Storia Patria is a museum/library rich in manuscripts and other printed media which document the rich history of Genoa. It is open daily from 09:30-12:30 and 15:00-19:00 and admission is free. The Galata Museo del Mare is approximately a 15-min walk from the Societa Ligure di Storia Patria and at the heart of the city's historical center.

Note: For additional results involving astronomical clocks and astrolabes (with astrolabe quadrants) from around the world, please click here.