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 photogenic astrolabe below is part of the extensive scientific instruments gallery at Museo Civico di Modena. It is constructed using gold and silver plated brass and measures 173mm in diameter. Although a specific craftsman has not been identified, it is believed to be Italian and to have been constructed between the latter part of the 16th century and the early part of the 17th century AD. The astrolabe is accompanied by two tympanums which serve the latitudes of 45° and 48° while the rete is characterized with approximately 30 star pointers. The double-armed rule is plain with no inscriptions whereas the rete is documented in Latin. The periphery of the mater is characteristic of many Italian/Latin astrolabes where the 24-hr clock is denoted by two sets of inscriptions ranging from I to XII. As noted, the astrolabe is accompanied by two latitude plates, thus being 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 Museo Civico di Modena is the primary civic museum in Modena. It is housed within the Palazzo dei Musei which is comprised of four museums including Museo Civico di Modena with the latter having a particularly rich collection of scientific and musical instruments and rich sections related to archaeology, ethnology and art paintings gathered across fifteen thematic rooms. The museum is open daily between 09:00 and 12:00 (Tuesday to Friday) and 10:00 to 19:00 on weekends with admission being free.

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