Latitude

• Parallels of Latitude are east west lines measured north or south from the Equator to 90° at the Poles.
• When used with Longitude they can identify any geographical location in the world.

Calculation of Latitude using the Gnomon

• Sailors in the Ancient World could easily calculate their Latitude by Day or Night using a Gnomon.

• By Night

  • Using a Gnomon, the angle of the North Star (Polaris) above the Horizon can be measured. The North Star is always directly above the North Pole..
  • When the North Star appears directly above the observer at 90°, he is at the North Pole.
  • When the North Star appears on the Horizon at 0°, he is on the Equator.
  • If the North Star is sighted 10° above the Horizon, then the observer’s vessel is on the 10° Parallel of Latitude.
  • The angle can also be roughly measured by placing the fist on the Horizon, which is roughly equal to 10°, and counting the number of fists to reach the North Star.

• By Day

  • The Sun’s height at Noon above the Horizon depends on the geographical location of the observer.
  • Using a Gnomon, the length of the shadow of the Sun along the Gnomon, will give the angle above the Horizon.
  • Today, this can be then looked up in tables for Solar Declination to find the observer’s location.
  • The Ancient World would depart from a point on a known Parallel of Latitude, and then keep heading due east or west until they reached the destination island, inlet or port.

Calculation of Longitude

• Longitude