Description: Astrolabes had a multitude of uses: determining the local time, finding the altitude of celestial bodies, finding the direction to Mecca, surveying, and triangulation. Many later models were also inscribed for use as rulers and protractors, or with star charts.
As some of the most sophisticated and beautiful tools for navigators and astrologers, astrolabes were also a symbol of intelligence and sophistication. Many astrolabes have been discovered that had serious errors, such that a real practitioner would immediately have noted them as fakes. These were probably sold to rich individuals who wanted to seem sophisticated to their guests.
The "mariner's astrolabe" was a much simpler instrument, designed for the pitching decks of ships rather than use on land.
Usage Dates: ~200 BCE to the 17th century
A beautiful and ornate astrolabe from the Harvard Museum of Historical Scientific Instruments.
A close-up of the previous astrolabe. Visible features include hour marks, constellation names, celestial coordinates, and multiple sets of inscribed angles.
Another astrolabe close-up, showing a maker's mark and an inscribed ruler.
A diagram of how an astrolabe might be used much like a sextant, to find the altitude of a star.
A sketch of an Islamic astrolabe from 1208.
Videos: Astrolabe Overview
Using an Astrolabe
The Institute of Navigation's Navigation Museum has a page on the Mariner's Astrolabe.
More detail on how astrolabes work from HowStuffWorks.com.
A Description of the Astrolabe translated from a text by Severus Sabokt, circa 650.
An in-person demonstration of an astrolabe, in a TED Talk by Tom Wujec.
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