Dioptra

• The Dioptra was a sighting line attached to a protractor, which enabled the elevation of a celestial object to be read in degrees.
• It was used in Ancient Astronomy from the 3rd century BCE until the 2nd century CE.

History

• The Dioptra was used by the Ancient Greeks in the third century BCE to calculate the positions of the Stars
• Euclid refers to the Dioptra in his Works.
• By the second century CE, it had been replaced by the Armillary Sphere, which was used by Ptolemy (c.150 BCE).