Navigation by the North Star

1
Navigation by the North Star

• In the Age of Exploration, the open ocean was a
  dangerous place for mariners.
• Good navigation was vital for survival.
• The North Star was important for getting around.

2
How to Find the North Star

• You 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.

3
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.

4
Stars Motion Across the Sky

• Stars 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.

5
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.

6
The Importance of the North Star

• The 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.

7
How the North Star is Viewed from Earth

• The North Stars 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.

8
The North Star At the North Pole

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

9
The North Star At the Equator

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

10
Finding Your Latitude

• If 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

11
The Sextant

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

12
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