What invention made it possible to calculate latitude? Why couldn't Columbus calculate longitude?

Question 1:

Latitude was often measured by using the quadrant and the astrolabe.

Question 2:

Measuring longitude at sea was extremely difficult in the past. The lack of a stable surface to work from and the inability to repeat determinations over time made it impossible to use the methods that were used on land. Many European countries promised prizes and riches to those who could figure out a way to do it, in one of the largest scientific enterprises in history.