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 brass astrolabe below is one of four astrolabes currently on display at the Victoria and Albert Museum in London and is credited to Muhammad Khalil with engraving by Muhammad Mahdi, both of Isfahan, Iran. The former (Muhammad Khalil) was a very prolific astrolabist in Isfahan with at least 30 of his works surviving to this date and on display in various museums around the world. The astrolabe is dated 1667 AD and measures 18.6 cm in height (with the throne included). The throne is decorated with floral patterns and is devoid of any text such as verses from Qur'an. The mater's outer ring is engraved in Arabic and invariably contains blessings on The Prophet Muhammad and the 12 Shi'a imams. The rete is particularly decorated with at least twelve interconnected complex patterns of stems and leaves which are used as star pointers; a very characteristic feature of astrolabes produced in Isfahan during the 16th and 17th centuries. The assymetrical rule is very basic and quite truncated. No information is available as to the availability of tympanums but it is clear in the image below that the plate in use is latitude-specific, thus making the astrolabe planespheric in nature, for it projects the three-dimensional celestial sphere onto a two-dimensional plane comprised of disks with the latter correcting for differences due to latitude. 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 Victoria and Albert Museum in London is one of the premier museums in the city with over 2.8 million works in its collection comprised of five thousand years worth of human creativity and inspiration. The foundation stone was laid by Queen Victoria in 1899 with the museum having expanded dramatically to now include five venues across London with the South Kensington branch having four astrolabes currently on display (room 42: Islamic Middle East section; room 99: Photography; and room 116: Metalware). The museum is open daily between 10:00 and 17:45 (10:00 to 22:00 on Fridays) and admission is free with no advance booking required. Access to the museum is trivial using London's undergound tube and where one exits at the "South Kensington" station (easily reachable by the District, Circle and Piccadilly lines) and follows an underground tunnel approximately 750 meters in total length. A brief walk leads to the proper underground entrance to the V&A Museum approximately halfway through the tunnel. Walking the full length of the tunnel leads to an exit above ground and which immediately leads one to the Science Museum no more than 20 meters away to the right as they exit (the Science Museum is physically across the street from the V&A Museum).

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