What purpose does the sextant serve in navigation?

The sextant is an essential instrument in navigation primarily used for measuring angles, particularly the angle between a celestial body (such as the sun, moon, or stars) and the horizon. This angle is crucial for determining a vessel's latitude and longitude. By accurately measuring the angle, navigators can plot their position on a nautical chart or use it in celestial navigation calculations to find their exact location on the earth's surface.

Other options, while they may seem relevant, do not accurately reflect the primary function of a sextant. For example, measuring distances would involve different tools such as radar or ranging devices. Calculating speed typically relies on a log or a GPS system, and determining water depth requires a depth sounder or sonar rather than a sextant. Thus, the role of the sextant is specifically linked to its ability to measure angles effectively, making it a critical tool for navigators throughout history.