Definition
A handheld optical instrument used in celestial navigation to measure the angle between a celestial body (such as the sun, moon, or a star) and the visible horizon. The measured angle, combined with the exact time of observation and published celestial tables, allows the navigator to determine a line of position and ultimately a fix on the Earth's surface.
Plain English
A device that measures how high a star, the sun, or the moon appears above the horizon. By knowing that angle and the exact time, a navigator can work out where on Earth they are.
Context Anchor
Seen in older long-range, overwater, and celestial navigation discussions, especially before modern radio and satellite navigation became common.
Derivation
From the Latin sextans, meaning 'one sixth.' The instrument's arc covers one sixth of a full circle (60 degrees), which is enough to measure angles up to 120 degrees thanks to its mirror system.
Why Pilots Care
Enables accurate position determination without reliance on radio or satellite signals, critical for long overwater flights before modern navigation systems.
Analogy
A sextant is like a very precise protractor used while looking at the sky. Instead of measuring an angle on paper, it measures the angle between the horizon and a body in the sky.
Intuition Check
A sextant does not directly tell you your position. It measures an angle; the navigator uses that angle with time and calculations to work out position.
Example Sentence 1
Before satellite navigation, long-range aircraft carried a sextant so the navigator could fix the airplane's position over open ocean.
Example Sentence 2
In training for emergency navigation, pilots practice taking sextant sights from the cockpit to maintain positional awareness.