Pole Star (Polaris, Alpha Ursae Minoris)

Nocturnal, 1702

This nocturnal allows you to tell the time at night. As the Earth turns, the stars appear to move across the sky. Tracking their positions allows you to use the night sky as a giant clock. Set the date on the outer ring and view the Pole Star through the centre hole. Next, turn the long arm until it lines up with certain stars and read the time off the inner dial.
Electrotype replica of a 16th-century mariner’s astrolabe, 1580-88

In the 1500s sailors needed to measure the angle of the Sun or the Pole Star above the horizon to help determine their latitude – not an easy thing to do on a pitching deck. The mariner’s astrolabe has cut-out sections to prevent buffeting from the wind and a heavy brass ring to keep it steady. This replica is based on an original thought to have been on board a ship in the Spanish Armada of 1588.
Sextant, 1770-80

Until satellite navigation became widespread, this type of instrument was a vital tool for sailors and aviators. It is called a sextant because the metal arc is one-sixth of a circle. Looking through the coloured glass filters, an observer could measure the altitude of bright objects such as the Sun or Moon without risking eye damage. Captain Cook used a sextant similar to this one to navigate around the Pacific islands in the 1770s.