Looking to the Sun and stars navigators began using special instruments to find latitude at sea.
Mariners relied on the Sun and stars to tell time and determine their place on the featureless ocean. To find latitude, they came to use angle-measuring instruments, which became increasingly accurate toward the end of the 1400s.
On a starry night in the northern hemisphere, a mariner could figure out latitude fairly easily by measuring the angle between the North Star and the horizon. On fair days, the Sun provided the most reliable readings.