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Longitude by Lunars

June 12 @ 10:00 am - 4:00 pm BST


An intermediate level class in the famous method of finding longitude by observing the Moon’s angular separation from the Sun and bright stars. Mystic Seaport Museum’s class in “lunars” has been the only class offered on the topic of lunars anywhere on Earth.

Lunars were widely used at sea in the early 19th century in the era before chronometers became common. Observing with a fine sextant, 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.

Participants in this workshop 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 and Bowditch and Slocum.

Taught by Frank Reed, the world’s premier expert on lunars and a recent guest expert in celestial navigation on Neil deGrasse Tyson’s StarTalk science talk show on The National Geographic Channel.

  • Saturday & Sunday, 10am-4pm both days.
  • Requirements: an introductory course or equivalent in the the use of a sextant and other basic concepts of celestial navigation.
  • Previous attendance in our “Celestial Navigation in the Age of Sail” is suggested but not required.
  • High school level math skills and a basic familiarity with trigonometry are recommended.


June 12
10:00 am - 4:00 pm BST
Event Category:


Reed Navigation
(401) 644-6012


Royal Observatory Greenwich
Blackheath Ave
Greenwich, London SE10 8XJ United Kingdom
+ Google Map
+44 (0)20 8312 6565

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