Armillary sphere
Esfera armilar
- Date
- c. 255 BCE · confidence medium
- Place
- Alexandria, Egypt
- Credited to
- Eratosthenes (tradition); perfected by Hipparchus and Ptolemy
- People
- 👤 Eratóstenes276 BCE–194 BCE
- Field
- Knowledge & symbols
⚠️ Disputed: the sources disagree.
What it is
A model of graduated rings representing the equator, ecliptic, meridians and tropics, used to observe and calculate the coordinates of celestial bodies. A central instrument of mathematical astronomy for 1,800 years.
China built independent armillary spheres (Luoxia Hong, 104 BCE; Zhang Heng, 125 CE, water-powered).
What it led to
- Star catalogues with coordinates (Hipparchus, the Almagest)
- The discovery of the precession of the equinoxes
- Teaching of geocentric cosmology in the West, Islam and China
- Positional astronomy for navigation and the calendar
Built on
- Gnomon and graduated sundialc. 560 BCE
- Euclidean axiomatic geometryc. 300 BCE
- Euclidean geometry
- Babylonian astronomy
Made possible
- Antikythera mechanismc. 100 BCE
- Zhang Heng's water-powered armillary sphere125 CE
- Early planispheric astrolabec. 150 CE
- Ptolemaic geocentric model (Almagest)c. 150
- Astronomical quadrantc. 850
- Torquetumc. 1260
- Tycho Brahe's precision instruments1582
- Honcheon Sigye armillary clock1669
- Zhang Heng's hydraulic armillary sphere