The device that measured the positions of the sun and stars to determine a ship's location is called a sextant.

Here's how it works:

* Measuring Angles: A sextant measures the angle between the horizon and a celestial body (sun, moon, or star).

* Celestial Navigation: This angle, along with the time of the observation, allows navigators to calculate their latitude and longitude using tables or specialized software.

* Precise Measurements: Sextants are incredibly precise instruments, capable of measuring angles to within a fraction of a degree.

The sextant was an essential tool for navigation for centuries, especially before the advent of modern electronic navigation systems. It remains a valuable backup tool even today.