Which navigational instrument helped determine the altitude of celestial bodies?

• A. The Map
• B. The Compass
• C. The Telescope
• D. The Astrolabe/Quadrant

Answer: (D)

Measuring how high a celestial body sits above the horizon is the key idea here. Instruments built to gauge that angle—the altitude—are the astrolabe and the quadrant. Sailors would sight the Sun or a star through one of these devices, read the angle between the horizon and the body, and then use tables to translate that angle into their geographic position or local time. The astrolabe provides a portable way to measure altitude with a marked scale, while the quadrant is a simpler, quarter-circle instrument that uses a plumb line to read the altitude. These tools were fundamental to celestial navigation long before more modern devices existed. The other options don’t perform this altitude measurement: maps aid planning, the compass indicates direction, and a telescope magnifies objects but isn’t used to measure the altitude angle for navigation.