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 Mecca for prayer. It is believed that 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. 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 iron astrolabe quadrant below is one of approximately twenty-five astrolabe quadrants on display at Museo Galileo in central Florence. Astrolabe quadrants were simplified versions of the more complicated standard astrolabe and were usually made either of wood or brass with a very small number made of other materials including iron and ivory. The iron quadrant below measures 28.3 cm in height and 27.9 cm in width, is dated from the 16th century AD and was made by the French instrument maker Jean Giamin (his signature is left of center just above the arc with the altitude demarcations) and who worked in Rome during the latter part of the 16th century producing astrolabes and sundials. As noted earlier, this quadrant is quite unique due to the fact that the quadrant is made of iron and, hence, is darker than the usual colour one encounters with gilted brass instruments. As is the case with all quadrants, a graduated arc along the quadrant's curved periphery at the bottom representing 90 degrees starts from the bottom left corner and continues onto the right corner with demarcations and text for every ten degrees. Immediately below is a similar arc but with demarcations at every five degrees and which is followed by a supplementary arc below it with equally spaced squares, alternating in shading, with five such squares for each marking in the arc immediately above and which effectively provide five one-degree markings for each five-degree interval. The apex of the quadrant normally holds a plumb bob which swings depending on the angle produced when aligning the quadrant's sighting scope with the celestial object of interest, thus immediately providing the altitude of the object such as the daytime Sun using the aforementioned graduated arcs. The determination of the altitude of a celestial object immediately allows one to identify the local time and, hence, astrolabes and quadrants were vital timing devices and clocks. A shadow square starting at the apex of the quadrant with references to "Umbra Versa" and "Umbra Recta" dominate the front plate and provides the respective vertical and horizontal scales whereas a rotating alidade helps establish the angle.

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 impressive Museo Galileo (Galileo Museum) and which was originally named Museo di Storia della Scienza (History of Science Museum) owing to its rich collection of scientific instruments including many astrolabes, horary quadrants, nocturnals, sundials, armillary spheres as well as Galileo's instruments including his telescopes. The museum's collections are displayed across two floors and eighteen thematic rooms including "Astronomy and Time" (Room II), "The Science of Navigation" (Room V), "The Science of Warfare" (Room VI), "Galileo's New World" (Room VII), "After Galileo: Exploring The Physical and Biological World" (Room IX), "The Spectacle of Science" (Room XI), "Measuring Natural Phenomena" (Rooms XV and XVI) and "Science at Home" (Room XVIII). Museo Galileo is open daily between 09:30 and 18:00 except for Tuesdays when it is open 09:30 to 13:00. Admission costs 13 euro and one can easily be engaged for a number of hours. The Museo Nazionale del Bargello with its magnificent collection of art and sculpture masterpieces is less than 400 meters to the north and only a few minutes away by foot with two astrolabes and an astrolabe quadrant in its collection and on display whereas the Fondazione Scienza e Tecnica with its impressive collection of scientific instruments from the nineteenth and twentieth centuries is 1200 meters further north and boasts a Galleria dell'Astronomia with a rich suite of astronomical instruments including an astrolabe.

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