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Lunars: Finding Longitude by Observing the Moon

An intermediate level class in the famous method of finding longitude by lunar distances, usually known for short as “lunars.” Lunars were widely used at sea in the early 19th century in the era before chronometers became common. By observing the position of the moon relative to the sun or stars, navigators used the moon as a great natural clock in the sky. From James Cook and Nathaniel Bowditch to Joshua Slocum, lunars were a challenge that proved a navigator’s skill.

Students in this class will learn the details of adjusting a sextant properly for shooting lunars, tricks for taking accurate sights, and easy methods for clearing these famously difficult observations. We’ll also talk about some of the interesting mathematics and astronomical theories that made lunars possible. For a modern celestial navigator or navigation enthusiast, there is no better test of your sextant and observing skills.

Weather permitting, students will have opportunities to take actual lunar observations, determining their longitude in the great tradition of Cook, Bowditch and Slocum.

Requirements: an introductory course or equivalent in the use of a sextant and other basic concepts of celestial navigation. High school level math skills and a basic familiarity with trigonometry are recommended.

Instructor: Frank Reed of Reed Navigation