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 However, the 2024 printed edition notes on page iv that the web companion was withdrawn as of January 2023.
**Publication contents** 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. Section D, Moon, offers detailed lunar positional information, including phases, mean orbital and rotation elements, mean month lengths,
- first_published
- 1767 (first edition of the British Nautical Almanac, published in 1766); 1852 (as American Ephemeris and Nautical Almanac); combined in 1981
Lore & Background
The material appears in sections, each addressing a specific astronomical category, including phenomena, time-scales, the Sun, Moon, planets, natural satellites, dwarf planets, stars, lunarcentric celestial objects, tables, notes, and a glossary. The Astronomical Almanac Online was a companion to the printed volume, designed to broaden the scope of the publication, not duplicate the data, but was withdrawn as of January 2023. The 2024 printed edition became available only one month in advance, in December 2023.
Reader's Guide
The Astronomical Almanac serves as a definitive reference for positional astronomy, used by astronomers, navigators, and researchers worldwide. Its significance lies in its role as a primary source for Solar System ephemerides, time-scale conversions, and celestial coordinate data, often incorporating the latest International Astronomical Union resolutions. The almanac's sections cover phenomena, time-scales, the Sun, Moon, planets, natural satellites, dwarf planets, stars, and lunarcentric objects, with detailed tables and explanatory notes. The Explanatory Supplement to the Astronomical Almanac (third edition, 2013) provides in-depth discussion of usage and data reduction methods. The almanac's history traces back to the 18th-century British and American navigational almanacs, and its joint publication since 1981 ensures continuity and global authority. Its legacy is cemented by its use of JPL Development Ephemerides and its role in standardizing astronomical data for both professional and practical applications.
Did You Know?
- The Astronomical Almanac is the direct descendant of the British Nautical Almanac and Astronomical Ephemeris (published since 1766) and the American Ephemeris and Nautical Almanac (published since 1852), combined in 1981
- The 2024 printed edition became available only one month in advance, in December 2023, whereas it used to be available up to one year in advance.
- The Astronomical Almanac Online was withdrawn as of January 2023.
- The almanac's Solar System ephemerides are based on the JPL Solar System integration 'DE440', created June 2020.
A Lineage of Navigation
The Astronomical Almanac carries within its pages a heritage stretching back nearly three centuries. 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. For nearly two centuries these two traditions ran in parallel, each serving its national community of navigators and astronomers. 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.
Gallery
Frequently Asked Questions
Who is Astronomical Almanac?
It is a long-running joint British and American reference work, first issued in 1766 under the auspices of the UK Hydrographic Office, that compiles fundamental celestial data for navigators, researchers, and the general public worldwide.
What are Astronomical Almanac's powers/role?
Think of it as the go-to annual compendium that turns raw celestial-mechanics calculations into practical tables and ephemerides for everyone from ship captains to space-mission planners. It also typically gets the first crack at publishing newly adopted IAU fundamental-astronomy standards before they appear anywhere else.
How does Astronomical Almanac's story end?
Spoiler: it doesn't—this is a living, annually renewed publication with no planned finale. Each new edition simply supersedes the last, so the narrative effectively resets every year.
Why is Astronomical Almanac important?
Because it unifies contributions from institutions on both sides of the Atlantic into a single authoritative volume that the international community relies on for consistent, vetted celestial reference values. Its status as the first outlet for new IAU standards gives it a quasi-setting-the-baseline role in fundamental astronomy.
Who are Astronomical Almanac's key collaborators?
The credit page lists a who's-who of celestial-mechanics outfits, including the UK's Nautical Almanac Office, the US Naval Observatory's ephemeris team, JPL, the IAU's Standards of Fundamental Astronomy group, Paris's IMCCE, and the Minor Planet Center.
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