A sextant is used in nautical navigation measure the angle between two visible objects. The angle, and the time it was measured, can be used to calculate a position line on a nautical or aeronautical chart. A common use of the sextant is to sight the sun at solar noon and to measure the elevation (altitude) angle at night to measure the elevation angle from the horizon plane to Polaris to find one’s latitude. Since the sextant can be used to measure the angle between any two objects, it can be held horizontally to measure the angle between two landmarks.
Property of the W&L Physics & Engineering Department
“Sextant,” Digital Exhibits at Washington and Lee University Library, accessed September 22, 2017, http://omeka.wlu.edu/items/show/207.