Leonardo da Vinci studied an astrolabe for measuring the angle between a star and the horizon.
An astrolabe is a portable instrument used to model the sky and measure the altitude of celestial objects. By aligning its sighting device with a star or the Sun, a user could determine an angle above the horizon. That information supported timekeeping, surveying, and traditional astronomical calculations.
Leonardo’s notebooks include diagrams and studies of astronomical instruments, reflecting his interest in geometry, observation, and practical measurement. The astrolabe was not a telescope: it measured positions using angular geometry, while a telescope magnifies distant objects.
Astrolabes existed long before Leonardo and were used across the Greek, Islamic, and European scientific traditions. His work represents Renaissance study and refinement of an established instrument, not its original invention.