Server Costs Fundraiser 2024

Help our mission to provide free history education to the world! Please donate and contribute to covering our server costs in 2024. With your support, millions of people learn about history entirely for free every month.
$3810 / $18000


The astrolabe is an astronomical instrument used from around the 6th century to measure time and position by determining the altitude of heavenly bodies like the Sun and certain stars. Measurements were taken in reference to the viewer's horizon and the meridian and using a representation or map of the sky with a measuring scale engraved on the instrument itself.

More about: Astrolabe


  • 100 CE - 170 CE
    Ptolemy describes the principle of the astrolabe - sterographic projection.
  • c. 1000 CE
    Knoweldge of the astrolabe filters through Muslim Spain to the rest of Europe.
  • 1391 CE
    Geoffrey Chaucer wrties an explanation of how to use an astrolabe in his Tractatus de Conclusionibus Astrolabii.
  • 1510 CE
    Johannes Stoeffler explains the astrolabe in Elucidatio fabricae ususque astrolabii.