Astronomical Almanac
Joint UK/US almanac providing fundamental astronomical data worldwide.
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The Astronomical Almanac is produced by the United Kingdom Hydrographic Office, drawing on data from scientists across the globe. Its major contributors, listed on page vii, include H.M. Nautical Almanac Office, the Nautical Almanac Office of the U.S. Naval Observatory, the Jet Propulsion Laboratory, the IAU Standards of Fundamental Astronomy initiative, the Institut de Mécanique Céleste et des Calcul des Éphémerides, and the Minor Planet Center.
It serves as a global reference for fundamental astronomical data and is frequently the first publication to adopt new International Astronomical Union resolutions. The almanac primarily contains Solar System ephemerides based on the JPL DE440 integration (completed in June 2020), along with catalogs of selected stars and extragalactic objects. Its material is organized into sections, each covering a specific astronomical category, and includes references, explanations, and examples.
Previously available up to a year in advance, the 2024 edition was released only one month ahead, in December 2023. The Astronomical Almanac Online was a companion to the print edition, designed to expand the publication’s scope rather than duplicate its data. It offered ancillary information and data best presented in machine-readable form. However, the 2024 printed edition notes on page iv that the web companion was withdrawn as of January 2023.
Section A, Phenomena, covers seasons, Moon phases, planet configurations, eclipses, transits of Mercury or Venus, sunrise/set and moonrise/set times, and twilight. Many of these data are previewed in Astronomical Phenomena, a joint publication by USNO and HMNAO. Section B, Time-Scales and Coordinate Systems, includes calendar information, time-scale relationships, universal and sidereal times, Earth rotation angle, celestial coordinate system definitions, frame bias, precession, nutation, obliquity, the intermediate system, Earth’s position and velocity, and Polaris coordinates.
Previews also appear in Astronomical Phenomena. Section C, Sun, provides detailed positional data for the Sun, such as ecliptic and equatorial coordinates, physical ephemerides, geocentric rectangular coordinates, transit times, and the equation of time.
A Lineage of Navigation
Its British ancestor, the Nautical Almanac and Astronomical Ephemeris, first appeared in 1766, serving mariners who needed reliable celestial data for safe passage across open oceans. In 1960, that long-running title was shortened to The Astronomical Ephemeris. On the other side of the Atlantic, the American Ephemeris and Nautical Almanac had been in continuous publication since 1852. In 1981, the two lineages were finally merged under the single banner of The Astronomical Almanac, a union that reflected the increasingly international character of fundamental astronomy.
The combined publication is now issued by the United Kingdom Hydrographic Office, with data contributions flowing in from institutions on both sides of the Atlantic and beyond. This genealogy—from separate national almanacs to a single global reference—mirrors the broader consolidation of astronomical practice into a shared, standards-based enterprise.
The Architecture of Data
The Almanac is organized into lettered sections, each devoted to a distinct astronomical category. Section A gathers the great celestial phenomena: seasonal markers, lunar phases, planetary configurations, eclipses, transits of Mercury and Venus, and the daily rhythms of sunrise, sunset, moonrise, and twilight. Sections B through G walk the reader from time scales and coordinate frameworks through the Sun, the Moon, the major planets, and the natural satellites of the outer worlds, down to dwarf planets, bright minor planets, and periodic comets.
The underlying Solar System ephemerides rest on the JPL Development Ephemeris DE440, a numerical integration produced in June 2020. Section H addresses stars and stellar systems, while Section K supplies practical tools such as Julian dates, astronomical constants, and interpolation methods. Every section is accompanied by explanatory notes, worked examples, and references to source material, making the volume both a data repository and a pedagogical resource for the working astronomer.
A Global Consortium of Expertise
No single institution could produce the Astronomical Almanac alone. Page vii of the volume lists the major contributors to its various sections, and the roster reads like a who's-who of fundamental astronomy. The H.M. Nautical Almanac Office of the United Kingdom Hydrographic Office and the Nautical Almanac Office of the United States Naval Observatory form the core editorial partnership. The Jet Propulsion Laboratory at the California Institute of Technology supplies the Solar System ephemerides, while the IAU Standards of Fundamental Astronomy initiative provides the coordinate-system standards.
The Institut de Mécanique Céleste et des Calcul des Éphémerides at the Paris Observatory contributes its own expertise, and the Minor Planet Center in Cambridge, Massachusetts, feeds in data on small Solar System bodies. The Almanac is also recognized as a worldwide resource for fundamental astronomical data and frequently serves as the first publication to incorporate new International Astronomical Union resolutions, cementing its role as a bridge between the global research community and the practicing astronomer.
Adapting to a Digital Age
The Astronomical Almanac has not stood still. For many years, the printed volume was available up to a full year before its target date, giving navigators and observers ample planning time. By the 2024 edition, however, the lead time had shrunk to roughly one month—the 2024 volume went on sale in December 2023. The publication also once maintained a digital companion, the Astronomical Almanac Online, designed not to duplicate the printed data but to extend it with machine-readable tables and ancillary information better suited to a screen.
That web companion was formally withdrawn as of January 2023, a decision noted on page iv of the 2024 printed edition. Looking forward, the 2025 almanac marks further structural changes: the stellar data in Section H has been pared down to navigational stars, spectrophotometric standards, and ICRF3 radio-source positions, with readers directed to the USNO website for the fuller catalog. Meanwhile, Section J now presents celestial objects as seen from the lunar south pole, replacing the earlier list of ground-based observatories—a quiet acknowledgment of humanity's expanding observational vantage points.
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Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Astronomical Almanac (CC BY-SA 4.0).
- Word definitions: the Codexery glossary, each quoted from its Wikipedia article.
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