Almanacs, nautical and astronomical

Astronomical Almanac

A continuous publication every year since 1767, The Astronomical Almanac is a remarkable success and an excellent example of international scientific cooperation. It well deserves its international standing as a standard resource for fundamental astronomical data.

The history of The Astronomical Almanac begins with the stars and the needs of sailors to navigate safe waters. Today, of course, there are precise satellites to tell you where you are. The Global Positioning System (GPS) is used in the United States.

Nonetheless, we still need the stars. For example, most satellites use star trackers to orient themselves in space. Radio telescopes monitor distant quasars to tell us where the Earth is pointed in inertial space. From these studies we follow the rotation of the Earth. It is the rotation of the Earth that ultimately tells us what time it is. So we depend today as we always have on the stars and the information they give us.

And so begins the history of The Astronomical Almanac.

It starts in 1767

The British produced the Nautical Almanac and Astronomical Ephemeris - just the thing for celestial navigation on those long sea voyages. Both the British and American navies used the book.

One of the things this book provided was an ephemeris of the Moon (a list of where the Moon would be at any given time during the next year). The ship's navigator used the Method of Lunar Distances to determine longitude. It is not a particularly simple method. The navigator had to be expert in spherical trigonometry.

In 1849 the Americans entered the picture.

The American naval appropriations act of 3 March, 1849 authorized the preparation and publication of data necessary for navigation. The U.S. Congress established the U.S. Nautical Almanac Office and funded the production of the American Ephemeris and Nautical Almanac. The first edition appeared in 1855. It contained sidereal time for the Greenwich meridian, lunar distances, and ephemerides of the Sun, Moon, and planets. It also contained transit ephemerides of solar system objects and some stars for Washington, DC. The eclipse maps were there, and also a list of active observatories. Already the book contained lots of useful information.

From the beginning it was recognized that producing an alamanc meant more than publishing rows of useful numbers. In the words of Lt. Davis, the first Superintendent of the U.S. Nautical Almanac Office, the work of the Office is:

"to supply precepts by which the movements of the heavenly bodies, as they appear to us from the earth, can be calculated." ..... the publication is to be "something more than just a book of mere results of calculations based upon rules furnished elsewhere; it should itself help to investigate the theories it is obliged to employ."

It takes scientists to prepare these almanacs. These scientists are specialists in fundamental and positional astronomy. And so the scientific communities began their work that still continues producing the best possible ephemerides and fundamental astronomical data. The books keep in step with the underlying science and provide the most current and most correct data available.

The Astronomical Almanac chronology

1767	First edition of The Nautical Almanac and Astronomical Ephemeris, published by Astronomer Royal of England.
1832	British Nautical Almanac Office forms
1834	Greenwich Mean Time appears in the book.
1849	U.S. Nautical Almanac Office forms
1855	first edition of The American Ephemeris and Nautical Almanac
1855	Both countries now publish almanacs.
1855	The US book publishes part of its data using a prime meridian in Washington DC as well as Greenwich.
1880's	Simon Newcomb begins developing new planetary theories and data. He was Superintendent of the US Nautical Almanac Office from 1877-1897.
1882	Both almanacs include ephemerides of more planets
1901	UK book incorporates Newcomb's tables and constants; the US follows a few years later.
1912	U.S book removes the Method of Lunar Distances from the book. The method of sight reduction is now the standard for navigation.
1912	U.S. Congress authorizes the international exchange of data and the official collaboration between the US and UK begins and continues today.
1914	Extract the marine navigation specific sections from the UK Astronomical Ephemeris and Nautical Almanac and publish separately as the UK Nautical Alamanc, abridged for the use of seamen.
1916	U.S. book now includes data from France, Germany, Spain and Britain
1916	Extract the marine navigation specific sections from The American Ephemeris and Nautical Almanac and publish separately as the U.S. Nautical Almanac
1919	Sun/Moon rise/set times first appear
1925	astronomers agree to start the astronomical day at midnight.
1934	U.S. book uses Greenwich hour angle for Sun, Moon, stars.
1937	First volume of the UK Air Almanac
1941	Almanacs adopt FK3 as the international celestial reference system
1941	first edition of the US Air Almanac
1950	Almanacs add Pluto
1952	The UK publishes The Abridged Nautical Almanac
1952	Almanacs add minor planets 1-4
1952	US book stops providing data using the prime meridian at Washington, DC
1953	Almanacs discontinue use of Greenwich Civil Time
1960	adopt ET - ephemeris time
1960	UK and U.S. versions become identical in content, each producing about 50% of the content.
1961	first edition of the Explantory Suplement
1968	adopt the 1964 International Astronomical Union constants
1981	Both almanacs change their name to The Astronomical Almanac
1981	add the Stars and Stellar Systems Section
1984	adopt the 1976 International Astronomical Union constants
1984	replace ET with TDB - Barycentric Dynamic Time
1984	adopt the DE200/LE200 Jet Propulsion Laboratory planetary ephemerides
2000	remove the lunar polynomials
2002	adopt TT - Terrestrial Time
2003	adopt the DE405/LE405 Jet Propulsion Laboratory planetary ephemerides add ephemerides of several minor planets add table of selected x-ray sources
2004	add tables of selected double stars and gamma ray sources remove the Besselian Day Numbers and Second Order Day Numbers. Replace the IAU1976 astronomical constants used in the computations with constants drawn from the IAU Best Estimates List, the IAU List of Cartographic Coordinates and Rotational Elements of Planetary Satellites, and the JPL DE405/LE405 ephemeris.