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 large and impressive brass astrolabe below is one of two astrolabes at the Specola Museum in Bologna. It is characterized with a diameter of 345 mm and easily weighs a few kilograms. The astrolabe was constructed by Gualterus Arsenius (ca. 1530-1580) who led a Flemish family very-well known for the manufacture of very high-precision scientific instrumnets and which was based in Louvain from about 1550 to late 1570's. The astrolabe is characterized with six accompanying tympanums which service a wide range of latitudes ranging from 32° to 51°. The rete includes a very impressive 47 star-pointers whereas the throne includes a pair of humanoid figurines on either side with Aresenius' name, location and date inscribed immediately below the throne. The bottom of the astrolabe includes a small compass. As noted, the astrolabe has a number of 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 University Museum System in Bologna (Il Sistema Museale di Ateneo dell'Universita di Bologna) overlooks fifteen individual and specialized museums in and around the city's university campus. One of these venues is the Specola Museum which is dedicated to astronomy. Located in the Specola Tower (built 1712-1726) where astronomical research was carried out as early as the early 1700's under the auspices of the Institute of Science at the time, the Specola Museum today is part of the Science Museum (Palazzo Poggi). The Specola Museum is compriszed of various thematic rooms which one encounters after climbing 272 steps to the top of the Specola Tower. The museum is normally open Tuesday to Friday between 10:00 and 16:00 with a modest admission fee of five euro but is temporarily closed due to structural damage to the Specola Tower and is expected to reopen during late 2024. (see here).

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