Navigation in the Age of Explorations

Using a Sextant (Quadrant)

Navigation by the North StarIn the Age of Exploration, the open ocean was a dangerous place for mariners. Good navigation was vital for survival.The North Star and a new instrument called a sextant helped navigation.

How to Find the North StarYou can find the North Star by locating the two bowl stars of the Big Dipper. Follow those stars in a straight line to the first bright star you see. That is Polaris.

Cassiopeia and the North StarYou can also use Cassiopeia to find the North Star.The North Star makes an arrow with the right-hand arch of Cassiopeia.

Stars Motion Across the SkyStars move across the night sky in circular arcs.This apparent motion is caused by the earth spinning on its axis.The North Star is at the center of the spin so it does not appear to move.

A Star Swirl on Film

Here is a photo of the night sky with the shutter left open. The stars appear to move in circular arcs. The North Star is the star in the center.

The Importance of the North StarThe position of the North Star is fixed throughout the night.And so, the angle of elevation of the North Star remains constant throughout the night.Therefore you can use the North Star to do two things: tell you where north is and tell you your latitude.

How the North Star is Viewed from Earth

The North Star’s position in the sky changes as you move from the North Pole to the Equator. It moves from being directly overhead to sinking down to the horizon.

The North Star: At the North Pole

At the North Pole, the North Star is directly overhead.

The North Star: At the Equator

At the equator, the North Star is at the horizon.

Finding Your LatitudeIf you measure the angle of elevation of the North Star, you can determine your latitude on the map.Angle of Elevation = Latitude on the Map

The Sextant

The sextant was a tool that mariners used to measure the angle of elevation of stars and the sun.

A Fisherman Using A Sextant

Here is a fisherman measuring the angle of elevation of the sun using a sextant.Sextants were used up until the 20th century