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 detailed brass astrolabe below is part of the Arti del Barocco section of the Torre Tesori collection on the second floor of the Musei Civici Palazzo Madama, in Turin (Torino). It measures 222 mm in diameter, has a dual-arm rule which 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 and, finally, is characterized with approximately 24 star pointers and which is typical given its size. The perimeter of the mater is not marked for a 24-hr clock (or two 12-hr segments) but has a scale between 0 and 90 for each quadrant and which permits for the extraction of altitude. The rete includes a single quatrefoil and four semi-quatrefoils. Although no craftsman is specified and which is typical for various latin astrolabes, the astrolabe is classified as Latin and is believed to be from the 14th century AD. It is accompanied by six 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). In a paper by Davis et al (Bulletin of the Scientific Instrument Society No. 146 (2020)), six astrolabes including the example below and presently in various museums show a distinct similarity involving the various components, thus suggesting the possible existence of a workshop in northern Italy during the middle of the 14th century AD.

Two astrolabes are available in Turin, namely one at the Musei Civici Palazzo Madama and the other at Musei Reali Palazzo Reale. However, the only specimen currently on display and available to the public is the astrolabe below and which is available at Musei Civici Palazzo Madama. The museum lies within the Palazzo Madama castle and which became a UNESO heritage site in 1997. The museum is characterized with over 70,000 works including impressive collections of paintings, statues, porcelain, gold and silver as well as decorative art and which is predominantly from the late Middle Ages to the 18th century. Musei Civici Palazzo Madama is open daily 10:00 to 18:00 except for Tuedays when it is closed with general admission costing 10 euro. A mere 170 meters further north, one will find the aforementioned Musei Reali Torino, also a UNESCO heritage site since 1997, and which is best known for being home to the famous Shroud of Turin with public viewing being planned once again for 2025. Also associated with Turin is the FIAT automobile brand as well as the Junevtus football team.

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