Early planispheric astrolabe
Astrolabio planisférico temprano
- Date
- c. 150 CE · confidence low
- Place
- Alexandria, Egypt
- Credited to
- Theory of Hipparchus and Ptolemy (Planisphaerium); instrument described by Theon of Alexandria (4th century)
- People
- 👤 Claudio Ptolomeo100–170
- Field
- Knowledge & symbols
⚠️ Disputed: the sources disagree.
What it is
A stereographic projection of the celestial sphere onto a flat disc with a rotating grid (rete) that allows the calculation of the time, the altitude of celestial bodies and the solving of spherical astronomy problems. The first portable astronomical computer.
Whether Hipparchus (2nd century BCE) already built an astrolabe is disputed; the complete instrument is securely documented only from Theon (c. 375 CE).
What it led to
- Islamic astronomy and the calculation of the qibla and prayer times
- Medieval astronomical navigation (the mariner's astrolabe)
- Teaching of astronomy in medieval universities
- Astronomical clocks with an astrolabe face
Built on
- Gnomon and graduated sundialc. 560 BCE
- Euclidean axiomatic geometryc. 300 BCE
- Armillary spherec. 255 BCE
- Hipparchus trigonometry and chord tablec. 150 BCE
- Hipparchus star catalogue and magnitude scalec. 129 BCE
- Antikythera mechanismc. 100 BCE
- Almagest and Ptolemy theoremc. 150 CE
- Ptolemaic geocentric model (Almagest)c. 150
- Hipparchus's stereographic projection
- Euclidean geometry