Which star is used to determine the north direction by sailors at night?

The Pole Star is also known as _______ or _______

Which hemisphere the Polaris is always visible to?

What was used to measure the passage of time on the ships by the early explorers?

Hourglass is also known as...

What instrument the navigators used to measure their position and determine their latitude on land or on the calm seas?

The astrolabe was not always an accurate tool at sea because it is difficult to take measurements on a rocking and wave-tossed ship's deck. __________ was a simplified version of the astrolabe to solve this problem.

____________ was much easier to use at sea than astrolabe.

Astrolabes, Mariner's Astrolabes and Quadrants were all not very accurate to be used as navigation aids.