AAS 207th Meeting, 8-12 January 2006
Session 46 History Potpourri
HAD Oral, Monday, 10:30-11:30am, January 9, 2006, Maryland C

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[46.05] All at sea without a clock - Longitude from lunar distances.

D.J.E. Floyd (STScI / ROE)

I present a brief history of the ``Lunar Distance" technique for determining Longitude at sea, as developed by Astronomer Royal Neville Maskelyne (1732-1811) and others. I illustrate this history using images and results from a recent (2001) BBC History project to re-enact part of Captain James Cook's first voyage, from near-shipwreck on the east coast Australia, back to the relative safety of Batavia (modern-day Djakarta).

I demonstrate the practical use of Lunars to determine longitude at sea, illustrated through comparison to GPS coordinates obtained along the voyage. During windows of lunar visibility, using new tables drawn up at HMNAO, we were able to match or exceed Maskelyne's stated accuracy of 30 nautical miles (0.5 degrees). Close to New Moon, dependent on our own skills of dead-reckoning, we prove far less able navigators than Cook and his cohort!

I acknowledge the enormous assistance of Catherine Hohenkerk of the HMNAO, Tanya Batchelor of the BBC, George Huxtable, John Jeffrey, and John Selwyn-Gilbert in researching this subject. I gratefully acknowledge funding from the BBC, and HM Bark Endeavour Foundation for the use of their glorious ship, the Endeavour.

The author(s) of this abstract have provided an email address for comments about the abstract: floyd@stsci.edu

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