The History of Navigation – Part 2 Astrolabe • Octant • Sextant Long before GPS, sailors crossed oceans using science and the sky. 🔹 Astrolabe Originated around 200 BCE and later adapted for ocean travel in the 1400s–1500s. Sailors used it to measure the height of the sun or stars above the horizon to determine latitude. 🔹 Octant Invented in the 1730s, the octant used mirrors to measure angles, allowing sailors to see the sun and horizon at the same time — far more accurate on a moving ship. �