The Astronomical Almanac is a joint publication of the Nautical Almanac Office in the United States and Her Majesty's Nautical Almanac Office (HMNAO) in the United Kingdom.

The U.S. Nautical Almanac Office is a division of the Astronomical Applications Department of the U.S. Naval Observatory (USNO). The U.S. Naval Observatory is the pre-eminent U.S. authority in the areas of time keeping and astrometry; determining and distributing the timing and astronomical data required for accurate navigation and fundamental astronomy.

H. M. Nautical Almanac Office is part of the United Kingdom Hydrographic Office (UKHO). H. M. Nautical Almanac Office continues a tradition, begun in 1767, of bringing the latest techniques in astronomy and computation to the publication of several almanacs, other books, software, and data services. UKHO is a Government Trading Fund and part of the Ministry of Defence and has been charting the world's oceans for over 200 years. It is the power behind the world-renowned Admiralty brand of products and services covering marine, defence, leisure and hydrographic expertise.

The Astronomical Almanac Online does not duplicate all the data from the book. It does, in some cases, provide additional information or greater precision than the printed data. Updates to this site occur regularly and accompany the publication of the book.

An additional resource is the Explanatory Supplement to The Astronomical Almanac. It contains a detailed description of the algorithms used for the data in the book and on this site. It is published on an irregular schedule. The most recent edition is 1992.

The Astronomical Almanac Online! 2020