Which description matches the function of an astrolabe?

Which description matches the function of an astrolabe?

• A. a device that records atmospheric weather patterns.
• B. instrument used to measure stars' positions to find latitude at sea.
• C. a tool for keeping time on long voyages.
• D. a device for determining longitude via clock measurements.

Answer: (B)

This item is about how celestial navigation worked—using the heights of stars to figure out where you are. An astrolabe is a tool for measuring the angle of celestial objects above the horizon. By sighting a star (or the Sun) and reading its altitude, you can relate that angle to your latitude, because the star’s known position in the sky (its declination) together with the measured height tells you how far north or south you are. Mariners used tables tied to the instrument to convert that altitude into a latitude reading, which is why measuring celestial positions to find latitude at sea is the best description of its function. The other descriptions describe weather recording, timekeeping, or determining longitude with clocks, none of which capture what the astrolabe primarily does.

This item is about how celestial navigation worked—using the heights of stars to figure out where you are. An astrolabe is a tool for measuring the angle of celestial objects above the horizon. By sighting a star (or the Sun) and reading its altitude, you can relate that angle to your latitude, because the star’s known position in the sky (its declination) together with the measured height tells you how far north or south you are. Mariners used tables tied to the instrument to convert that altitude into a latitude reading, which is why measuring celestial positions to find latitude at sea is the best description of its function. The other descriptions describe weather recording, timekeeping, or determining longitude with clocks, none of which capture what the astrolabe primarily does.