The Astrolabe: Using the Stars to Explore the Earth
The astrolabe, which means star taker in Greek, is a scientific instrument to make observations and calculations. Because early man recognized that stars moved in patterns and could be used to determine dates, times, and celestial events, travelers developed tools such as the astrolabe, which utilized the stars. While difficult to pinpoint the exact origin of the astrolabe, scholars often credit Greek astronomer Hipparchus with this invention around 200 B.C. Because the astrolabe did not depend on shadow or daylight, it was more accurate than previous tools such as the gnomon (Berthon 32). The gnomon is the part of a sundial that casts a shadow. Its scientific use extended into Europe and reached the West around the tenth century, and the Islamic world used it to ascertain prayer times and the direction of Mecca. Scientists employed the planispheric astrolabe to observe celestial objects, measure positions, and determine time. Others, including geographers, timekeepers, surveyors, and navigators, used astrolabes. The use of the astrolabe was pivotal in navigation because its use improved the consistency of ships’ headings.
The astrolabe, often made of brass and measuring six to eight inches in diameter, has a base known as a mater, marked with lines indicating hours and degrees. The mater encloses a plate, the tympan, with grid lines indicating altitude. Some astrolabes had interchangeable tympans to use at different latitudes (Watson). The tool includes a star map, or rete, to signify positions of stars. As the user turns the rete, the stars rise and set. Rotating rulers are on each side; the rule is on the front, and the alidade, a sighting device, is on the back (Watson). As users rotated these rings, they could determine time of day, predict sunrise or sunset, and determine altitude of celestial objects.
Sailors used a mariner’s astrolabe to determine the latitude of ships (Bullard). The astrolabe allowed sailors to maintain consistent headings even with cloudy skies and without being within sight of land (Law). As nations set off on expeditions to find more land and riches, employing accurate forms of navigation allowed sailors to find and return to new lands. John Law, who analyzed Portuguese transoceanic expansion, concluded that the establishment of a scientific commission to produce rules to calculate latitudes and generation of a record of latitudes of coastal features enabled the creation of practical instructions for sailing (241-3). Better navigation benefited sailors with more accurate routes and lessening the possibility of being lost at sea.
Interest in the instrument peaked as astrolabes were produced commercially and became smaller and cheaper (Hayton) and remained a popular tool until the middle of the seventeenth century (“Nicholas Copernicus”) when other instruments such as telescopes and clocks replaced the astrolabe. The astrolabe was an early scientific instrument used primarily for astronomy, religious observation, and navigation. Scientists using the astrolabe could tell time and predict celestial events with greater accuracy than earlier scientists. Religious groups determined daily prayer time as well as future religious events, and sailors better navigated the seas. Later navigational tools became even smaller and more accurate than the astrolabe.
“Astrolabe History.” University of Hawaii, Institute for Astronomy. 18 Apr. 2000, www.ifa.hawaii.edu/tops/astl-hist.html. Accessed 16 Oct. 2018.
Berthon, Simon and Andrew Robinson. The Shape of the World: The Mapping and Discovery of the Earth .Chicago: Rand McNally, 1991.
Bullard, Eric. “Astrolabe.” Salem Press Encyclopedia of Science, 2017. EBSCOhost, search.ebscohost.com/login.aspx?direct=true&db=ers&AN=87325832&site=eds-live. Accessed 16 Oct. 2018.
Harris, William. “The Technologies of Time.” How Stuff Works. 2012, electronics.howstuffworks.com/gadgets/clocks-watches/astrology-to-thank-for-clocks1.htm. Accessed 17 Oct. 2018.
Hayton, Darin. An Introduction to the Astrolabe. dhayton.haverford.edu/wp-content/uploads/2012/02/Astrolabes.pdf. Accessed 17 Oct. 2018.
Law, John. “On the Social Explanation of Technical Change: The Case of the Portuguese Maritime Expansion.” Technology and Culture. vol. 28, no. 2 1987, www.jstor.org/stable/3105566. Accessed 17 Oct. 2018.
“Nicholas Copernicus: Founder of Modern Astronomy.” Nicholas Copernicus: Founder of Modern Astronomy, Oct. 2004, pp. 10–42. EBSCOhost, search.ebscohost.com/login.aspx?direct=true&db=khh&AN=22198740&site=eds-live. Accessed 16 Oct. 2018.
Watson, Bruce. “The Astrolabe: Astronomy’s First Hot App: Loaded with Features, an Ancient Analog Computer Replicates the Sky’s Workings.” Sky & Telescope, no. 2, 2016, p. 24. EBSCOhost, search.ebscohost.com/login.aspx?direct=true&db=edsgbc&AN=edsgcl.439833392&site=eds-live. Accessed 16 Oct. 2018.