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. Typical of many European astrolabes, regrettably there is no reference to the craftsman or the date behind this work. However, several characteristics of the rete reveal the French origin of the astrolabe and which has been estimated to have been produced between 1300 and 1400 AD. All text on the rete is in Latin, thus suggesting a European influence. Similarly, the rete has one trefoil in the inner circle and another four semi-trefoils on the outer ring, thus strongly suggesting French influence. Furthermore, the rete is characterized with 33 star-pointers and which is a fairly large number given the size of the astrolabe (approximately 20 cm in width). The crown is plain with no engraved text or graphic and is also in the shape of a trefoil. Finally, the rete is single-armed, also devoid of any inscribed text and has a quatrefoil for securing it in place with the central pin which passes to the back of the astrolabe and connecting to the alidade. The latitude plate is characteristic of a planespheric astrolabe, 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.