Teaching and commentary
Ancient reports associate Hypatia with work on Diophantus, Apollonius and astronomical texts. Much of the evidence is indirect.
13 / ANTIQUITY TO THE RENAISSANCE
Hypatia of Alexandria
How high is a star? Astronomers answered with an angle above the horizon, measured on an astrolabe hung from its ring.
Explore the mathematics ↓
01 / ANGULAR ALTITUDE
Read the sky with a rotating arm
Turn the astrolabe’s sighting arm onto a star, then read the angle on its scale.
The instrument hangs from a ring so that gravity keeps its 0° line level. Hold it crooked, and the reading goes wrong.
How high is that star?
Height in the sky is measured as an angle above the horizon. Turn the astrolabe’s sighting arm onto a star.
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THE IDEAAltitude is the angle from the horizon to an object in the sky: 0° at the horizon, 90° straight overhead. Hanging the astrolabe from its ring keeps that zero line true.
The person behind the ideas
- Taught philosophy, mathematics and astronomy in Alexandria.
- Her pupil Synesius credited her contribution to an astrolabe he commissioned.
- Her birth date and the precise extent of her mathematical writings are uncertain.
More of the mathematics
A flat model of the sky
A full planispheric astrolabe also maps the sky onto a flat plate. This lesson isolates the simpler act of measuring altitude.