Sextant

navigation · astronomy · maritime

Finding location with stars. A sextant lets explorers measure the angle between a bright star (or the sun) and the horizon, which tells them exactly where they are on Earth. Sailors have used this trick for hundreds of years to cross vast oceans without getting lost.

Two clever mirrors. The sextant has two mirrors inside that bounce light back and forth. This double reflection lets you see both the horizon and a star at the same time, making it possible to measure the angle between them super precisely.

The name's geometry. A sextant gets its name because it measures one-sixth of a circle (that's what 'sextant' means in Latin). The curved part of the tool covers exactly 60 degrees, which is perfect for the angles sailors need to measure.

Still used today. Even though we have GPS now, ships and planes still carry sextants as backup. They work without batteries or signals, so they're reliable even in remote parts of the ocean or sky.

Requires a steady hand. Using a sextant takes practice because you need to hold it still while looking through the eyepiece and keeping the horizon lined up. Experienced navigators can measure angles so accurately that they're off by less than a mile over hundreds of miles of travel.