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 impressive large brass astrolabe below is part of the Galleria dell'Astronomia at the Fondazione Scienza e Tecnica (Science and Technology Foundation) in Florence. Regrettably there is a complete lack of information surrounding the astrolabe including date, craftsman and provenance (even a museum catalog number is blatantly absent). The astrolabe is relatively large with a diameter that could reach 30 cm. The outer ring of the mater is used to represent a 24-hr cycle but in two sets of 12-hr (I to XII) segments and which is a characteristic of astrolabes manufactured in Italy during the 13th and 14th centuries AD. The inscriptions throughout the rete are in latin, thus further suggesting that the astrolabe may be Italian in nature. The rete is characterized with approximately 24 star-pointers using slender curved pointers arising from bases with no particular geometry or indication of stellar magnitude. The single-armed rule is completely blank and without any engraved information potentially describing the craftsman and/or year of manufacture with the single arm deviating from the typical doubly armed rules characteristic of most astrolabes. The engraved contents immediately below the rete do not correspond in any way to a universal astrolabe, thus implicitly making this astrolabe planespheric in nature but without any indication for latitude and which would otherwise suggest its provenance. 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 historic center of Florence is characterized with a number of epic museums (with very impressive collections) which are a must-see while visting the city. One such museum is the Fondazione Scienza e Tecnica (Science and Technology Foundation) and which is one of three museums in Florence which has a collection related to astronomy and including the impressive astrolabe below in its Galleria dell'Astronomia. Fondazione Scienza e Tecnica is closed on Mondays but open on Tuesday through Friday between 10:00 and 16:00 and on weekends between 10:00 and 18:00 with admission being free to the Galleria dell'Astronomia. The museum's rich collection of scientific instruments (1800-1950 AD) and natural history as well as its planetarium are worthy of a multi-hour visit. The museum lies only 950 meters to the northeast of the stunning Cathedral of Santa Maria del Fiore with the iconic red dome in central Florence. Further south by 1100 meters one will find the magnificant Museo Nazionale del Bargello with its magnificent collection of art and sculpture masterpieces as well as two astrolabes and one astrolabe quadrant whereas another 350 meters yet further south one will come across the epic Museo Galileo whose rich collection includes over 20 astrolabes and a large collection of astrolabe quadrants.

Note: For additional results involving astronomical clocks and astrolabes from around the world, please click here.