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
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.
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:
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
|First edition of The Nautical Almanac and Astronomical Ephemeris, published by Astronomer Royal of England.
|British Nautical Almanac Office forms
|Greenwich Mean Time appears in the book.
|U.S. Nautical Almanac Office forms
|first edition of The American Ephemeris and Nautical Almanac
|Both countries now publish almanacs.
|The US book publishes part of its data using a prime meridian in Washington DC as well as Greenwich.
|Simon Newcomb begins developing new planetary theories and data. He was Superintendent of the US Nautical Almanac Office from 1877-1897.
|Both almanacs include ephemerides of more planets
|UK book incorporates Newcomb's tables and constants; the US follows a few years later.
|U.S book removes the Method of Lunar Distances from the book. The method of sight reduction is now the standard for navigation.
|U.S. Congress authorizes the international exchange of data and the official collaboration between the US and UK begins and continues today.
|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.
|U.S. book now includes data from France, Germany, Spain and Britain
|Extract the marine navigation specific sections from The American Ephemeris and Nautical Almanac and publish separately as the U.S. Nautical Almanac
|Sun/Moon rise/set times first appear
|astronomers agree to start the astronomical day at midnight.
|U.S. book uses Greenwich hour angle for Sun, Moon, stars.
|First volume of the UK Air Almanac
|Almanacs adopt FK3 as the international celestial reference system
|first edition of the US Air Almanac
|Almanacs add Pluto
|The UK publishes The Abridged Nautical Almanac
|Almanacs add minor planets 1-4
|US book stops providing data using the prime meridian at Washington, DC
|Almanacs discontinue use of Greenwich Civil Time
|adopt ET - ephemeris time
|UK and U.S. versions become identical in content, each producing about 50% of the content.
|first edition of the Explantory Suplement
|adopt the 1964 International Astronomical Union constants
|Both almanacs change their name to The Astronomical Almanac
|add the Stars and Stellar Systems Section
|adopt the 1976 International Astronomical Union constants
|replace ET with TDB - Barycentric Dynamic Time
|adopt the DE200/LE200 Jet Propulsion Laboratory planetary ephemerides
|remove the lunar polynomials
|adopt TT - Terrestrial Time
|adopt the DE405/LE405 Jet Propulsion Laboratory planetary ephemerides add ephemerides of several minor planets add table of selected x-ray sources
|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.