An instrument used to determine latitude by measuring the position of the stars.

• A. Compass
• B. Astrolabe
• C. Sextant
• D. Chronometer

Answer: (B)

Determining latitude from the position of the stars relies on measuring how high a celestial body sits above the horizon. The astrolabe is built to measure that altitude directly and translate it into geographic position. You sight a star, read the altitude angle on the instrument’s graduated circle, and then use the star’s known declination and time to work out your latitude. In the northern hemisphere, for example, measuring Polaris’s height above the horizon gives your latitude quite directly because Polaris sits near the north celestial pole—the higher it sits, the farther north you are. This made the astrolabe a primary tool for celestial navigation in many historical contexts.

A compass only shows direction, not position. A sextant also measures altitude to determine position, and can be used for latitude (and longitude with time), but the question points to the traditional instrument used specifically for measuring star positions to find latitude, which is the astrolabe. A chronometer measures time to help determine longitude, not latitude.