Meridian

• In Astronomy, the Meridian is a great circle passing through the celestial poles, the zenith and the nadir of the observer’s location.
• The Meridian is perpendicular to the Celestial Equator.

The Meridian on the Celestial Sphere

• A star crossing the observer’s Meridian can be used to calculate its Latitude.
• In the Age of Sail the navigator used Meridian Pairs, two stars that crossed the Meridian together, that were visible after sunset and before dawn.
• He planned voyages for a time of year when known stars would cross the Meridian, giving him the Latitude to find a particular island or coastal inlet.

Zenith Stars

• The Zenith stars are stars which pass through an imaginary point directly overhead the observer at a particular Latitude.
• Knowing the Latitude of Zenith stars means the Navigator can determine his Latitude when a particular star passes directly overhead.

Pole Star

• Because the North Star or Pole Star is directly overhead the North Pole, it will always be at the same angle above the horizon as the Navigator’s Latitude in the Northern Hemisphere.

Mintaka

• The Constellation of Orion rises in the East and Sets in the West.
• Mintaka, one of the three stars in Orion’s Belt, rises within one degree of due east and sets within one degree of Due West, wherever the Navigator is in the world.