Northstar[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.

Strategies to avoid getting lost Hugging the coast line Problem: limited where they could go To avoid getting lost Where they were • Latitude/longitude

Where they were going • Compass direction

Finding direction Stars and compass Disadvantages Stars not visible during day and bad weather Early compasses were unreliable • Lost magnetic charge • Ships motion made it difficult to get a steady reading • Compass needle points to magnetic north not true north

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.

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 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.

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 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.

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 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

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

Determining Longitude important aspects of navigation: direction, latitude, and longitude. Direction and latitude are relatively easy to determine. Practical measurements of longitude, on the other hand, stumped the greatest minds for centuries. The reason for the difference is that latitude is fixed by nature (the location of the poles), whereas longitude is arbitrary.

Using a protractor Line up center point of protractor with the point of your angle Put the 0 on the line Read angle Left of 90 outside Right of 90 inside

Constellations

Constellations

Circumpolar constellations What does circumpolar mean? Circumpolar means to circle around the pole. Circumpolar stars or constellations daily trace circles around the north celestial pole, without setting or dipping below the horizon. They move in a counterclockwise direction. On any given night, the constellation is visible during a portion of the circle; the rest is traced out when the constellation is hidden in the daylight sky.

Circumpolar constellations

Circumpolar Constellations

Circumpolar Constellations

Circumpolar Constellations

Circumpolar Constellations

Circumpolar Constellations