Navigation by Polaris

In the Age of Exploration, the open ocean was a dangerous place for mariners.

Good navigation was vital for survival.

Mariners used the North Star (Polaris) for navigation.

How to Find Polaris

You can find Polaris 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 Star

You 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.Polaris is at the center of the spin so it does not appear to move.

Star Trails

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

The Importance of Polaris

The position of Polaris is fixed throughout the night.

And so, the angle of elevation of Polaris remains constant throughout the night.

Therefore you can use Polaris to do two things: tell you where north is and tell you your latitude.

How Polaris is Viewed from Earth

Polaris’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.

Polaris: At the North Pole

At the North Pole, the Polaris is directly overhead.

Polaris: At the Equator

At the equator, Polaris is at the horizon which is 0o

If a ship is south of the Equator can it see Polaris?

Finding Your Latitude

If you measure the angle of elevation of the Polaris, 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