The familiar orange book, The Nautical Almanac, along with the chronometer, the sextant, a steady hand and a keen eye, are the resources needed to navigate by the stars. Even today celestial navigation remains a critical backup to GPS and other electronic navigation systems.
The British first published the Nautical Almanac and Astronomical Ephemeris in 1766, with data for 1767. In the United States, the naval appropriations act of 3 March 1849 authorized the preparation and publication of the data necessary for navigation. For this purpose the U.S. Nautical Almanac Office was established in the same year. The American Ephemeris and Nautical Almanac was first published in 1852, with data for 1855. The Nautical Almanac has been published separate from its parent publication in the UK since 1914, and in the U.S. since 1916. Since the unification of the Almanacs in 1958 the U.S. Nautical Almanac Office has produced The Nautical Almanac in full collaboration with Her Majesty's Nautical Almanac Office.
Initially the almanacs provided the data required for the method of lunar distances, a technically demanding and mathematically complex method of determining longitude before the invention of accurate clocks for shipboard use. The common availability of precise chronometers on ships beginning in the early 1800s, and the development of methods of "sight reduction" by Sumner, St.-Hilaire and others, provided an easier procedure for navigators to determine their position at sea. The almanacs provided the necessary data for these methods.
|1766||First edition of The Nautical Almanac and Astronomical Ephemeris appears, published by Astronomer Royal of England, with data for 1767. The book provided the information necessary for the method of lunar distances used to determine longitude.|
|1832||British Nautical Almanac Office is organized|
|1834||Greenwich Mean Time appears in the book.|
|1849||U.S. Nautical Almanac Office forms|
|1852||First edition of The American Ephemeris and Nautical Almanac appears, with data for 1855. The U.S. book publishes the data using two prime meridians: one in Washington DC and one in Greenwich.|
|1901||The UK book adopts the astronomer Simon Newcomb's tables and
the U.S. follows suit a few years later.
|1912||U.S. book removes data for the method of lunar distances|
|1912||U.S. Congress authorizes international exchange of data.|
|1914||The UK extracts the sections specific to marine navigation from the UK Nautical Almanac and Astronomical Ephemeris and publishes them separately as the UK Nautical Almanac, Abridged for the Use of Seamen.|
|1916||The U.S. book includes data from France, Germany, Spain and Britain|
|1916||The U.S. extracts the sections specific to marine navigation from The American Ephemeris and Nautical Almanac and publishes them separately as the U.S. Nautical Almanac, designed especially for navigators.|
|1919||Sun/Moon rise and set times first appear|
|1925||Astronomers agree to start the astronomical day at midnight to coincide with the beginning of the civil day. Civil time introduced with the notation GCT.|
|1934||U.S. book provides the Greenwich Hour Angle for Sun, Moon, and planets and the Sidereal Hour Angle for the navigation stars.|
|1950||Redesign of the almanac. Right ascensions discontinued.|
|1952||Washington ephemerides removed from U.S. book.|
|1953||Use of Greenwich Civil Time, first introduced in the 1925 almanac, is discontinued. It is replaced with Greenwich Mean Time, GMT.|
|1958||First year of the unified Nautical Almanac for use by the United States Navy and the British Royal Navy.|
|1971||The arguments of the dip table are given in both meters and feet.|
|1980s||UT replaces GMT in Nautical and Air Almanacs|
|1984||DE200/LE200 JPL planetary ephemerides adopted as basis|
|1989||Concise Sight Reduction Tables and Instructions for sight reduction by computer were introduced, making the Nautical Almanac a self-contained edition for navigators.|
|2003||DE405/LE405 JPL planetary ephemerides adopted as basis|
|2006||The 2006 edition uses Hipparcos astrometry for stars and improved precession and nutation algorithms consistent with IAU resolutions.|
|2014||The 2014 edition included more effective and deeper star finding charts.|
|2015||The 2015 edition adopted JPL's DE430/LE430 planetary ephemerides as its basis|
|2016||The 2016 edition included a new Polar Phenomena section.|