Astrolabe Facts

Astrolabe Facts
An astrolabe is an ancient device that has been used as a type of astronomical computer dating back to over 2,000 years ago. The astrolabe was considered to be the most popular astrological instrument until the 1650s when more accurate devices were developed. An astrolabe measures the position of the stars, which can help with navigation, determining the time, determining the time of year, latitude, and altitude of an object on the horizon. The astrolabe was historically a roughly six inch inscribed brass disc, but more features were added to the two dimensional celestial sphere over time. There were also smaller and larger versions of the astrolabe throughout history.
Interesting Astrolabe Facts:
An astrolabe is capable of measuring the position of celestial objects in the sky.
Astrolabes can measure the time of day or night when used as a mobile sundial. It can also be used to measure the altitude of the sun which provides a more accurate time of day or night.
Astrolabes are capable of measuring the time of year.
It is possible to use an astrolabe to determine an object's altitude on the horizon.
Astrolabes can be used to measure the current latitude, as well as the NPS orientation.
Although not known for certain, it is believed that the first astrolabes may have been created by Hipparchus in 150 BC.
The astrolabe is considered to be a combination of a diopter (multi angle measurement tool) and a planisphere (a type of star chart).
In the Middle Ages new features were added to the astrolabe which made them more useful for a variety of purposes.
Explorers and navigators often used astrolabes to help them stay on course or figure out where they were.
The most popular type of astrolabe was the planispheric astrolabe. This type of astrolabe projects the celestial sphere onto the equator.
The astrolabe created for mariners was a simple ring with markings to measure celestial altitudes.
It has been said that when Ptolemy (Greek writer, astronomer, mathematician, astrologer and geographer who lived from AD 100 to 170) recorded astronomical observations in Tetrabiblos (ancient 4 book text on astrology and philosophy) he used an astrolabe.
Some believe that it was actually Hypatia (daughter of Theon of Alexandria) that invented the astrolabe and not Hipparchus.
Astrolabes were much more developed in the Medieval Islamic world. They added angular scales, circles for azimuths, and used the astrolabe for finding the direction of Mecca, as well as got determining the time for morning prayers.
Abd al-Rahman al-Sufi, a famous Muslim astronomer born in 903, listed over 1,000 uses for the astrolabe including determining horoscopes, for navigation, astrology, keeping time, prayer, and astonomy.
The spherical astrolabe invented during the Middle Ages, was a combination of both the astrolabe and the armillary sphere.
The largest collection of astrolabes is located in Oxford, in the UK at the Museum of the History of Science.
There is a large and rare collection of astrolabes at the Adler Planetarium and Astronomy Museum located in Chicago, IL.
The Smithsonian National Museum of American History in Washington, D.C. houses an astrolabe collection.

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