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GMT and Longitude by Lunar Distance: Two Methods Compared From a Practitioner's Point of View

  • Eric Romelczyk
Abstract

This article discusses the technique of observing lunar distance - that is, angular distance between the moon and another celestial body - to establish universal time and longitude, from a practitioner's point of view. The article presents a brief overview of the principles underlying the lunar distance observation and its use in celestial navigation. A discussion follows of two different methods for finding universal time by observing lunar distance, Dr. Wendel Brunner's calculator-based method and the specialised inspection tables created by Bruce Stark. The article compares the two methods against each other for ease of use and accuracy. The author concludes that either method will provide satisfactory results, but that the technique of observing lunar distance is unlikely to regain relevance in the modern-day practice of navigation and is primarily useful as a skill-building exercise in making sextant observations.

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References
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Brunner, W. (2005). Longitude By The Method Of Lunar Distance. Resources, Starpath School of Navigation, LLC. www.starpath.com/resources2/brunner-lunars.pdf. Accessed 1 June 2017.
Lecky, S.T.S., and Allingham, W. (1918). Wrinkles in Practical Navigation. 19th ed. George Phillip & Son.
Maskelyne, N. (1767). The Nautical Almanac and Astronomical Ephemeris For The Year 1767. Commissioners of Longitude.
National Geo-spatial Intelligence Agency. (2017a). The American Practical Navigator; An Epitome of Navigation, Vol. 1. U.S. National Geo-spatial Intelligence Agency.
National Geo-spatial Intelligence Agency. (2017b). The American Practical Navigator; An Epitome of Navigation, Vol. 2. U. S. National Geo-spatial Intelligence Agency.
Raper, H. (1908). The Practice of Navigation and Nautical Astronomy. 19th ed. J.D. Potter.
Sadler, D.H. (1978). Lunar Methods for ’Longitude Without Time. The Journal of Navigation, 31(2), 244249.
Stark, B. (2010). Stark Tables for Clearing the Lunar Distance and Finding Universal Time by Sextant Observation. 3rd ed. Starpath Publications.
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The Journal of Navigation
  • ISSN: 0373-4633
  • EISSN: 1469-7785
  • URL: /core/journals/journal-of-navigation
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