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Astrolabes & Planespheres

Astrolabes were cherished during the middle ages, an astrological/astronomical slide rule, clock, calendar, star map on one side; a sextant, measuring device on the other side - all on one instrument; much more than a planesphere. Chauser's 'Treatise on the Astrolabe' is an extensive piece regarding the practices and uses of an astrolabe.

Astrolabes and planesphere's are basically the same thing - they both have a calendar corresponding to a siderial time, and an overlay depicting the celetsial sphere. The difference is an Astrolabe's overlay depicting the local celestial sphere is far more exact to the longitude, a planesphere's depiction of the celestial sphere is more general because it is within 20 degrees of the latitude.

An astrolabe also has a simple site, similar to a sextant to measure angles between objects, celestial or terrestial. This makes one perfect tool for hands-on learning of the celestial sphere - plotting sunrise/transit/sunset, moonrise/transit/moonset - bright star transits, planets, retrograde motions, the zodiak's relation to the eliptic, comets and anything else in the sky.

Making Your Own Astrolabe

All the formulas needed to create astrolabes like the one pictured above (this one is has Venice California specific overlay)are available on the internet. Most surviving astrolabes are antiques in a museum or they cost hundreds, even thousands of dollars. With a computer we can make functioning astrolabes that are are far more accurate then the ones we can buy.

We can make retes for any purpose, zodiak and sun, brightest stars, planet tracking; They can be personalized for you with overlays that are specific to: your local latitude(get others for various citys and latitudes you visit,) birthday, Zodiak Sun Signs, constellations, planetary movements, Sun - and any other "furniture" you may dream-up or desire. An astrolabe can also visibly bridge the gap between astrological and astronomical concepts.

The best resource I know of is the University of Hawaii's Astolabe pages. Here is everything you need to make your own astolabes; tailored to your own latitude and you can make overlays for any latitude you might visit. http://www.ifa.hawaii.edu/tops/astlabe.html