John Flamsteed (1646–1719), English astronomer and first Astronomer Royal, spent some forty years observing and cataloging more than 3000 stars visible from the Greenwich observatory. The official version of his catalog, containing 2,936 entries, was published posthumously by his wife Margaret in Historia Coelestis Britannica (London, 1725) under the heading Stellarum Inerrantium Catalogus Britannicus.

Flamsteed's catalog groups stars in 55 constellations: 46 of the 48 Ptolemaic constellations (Ara and Corona Australis are omitted entirely, and constellations that extend too far south are only partially covered) and 9 constellations that Flamsteed attributes to Hevelius, although the details are more complicated, as explained on Ian Ridpath's site Star Tales.

The so-called Flamsteed numbers assigned to stars by constellation, still in use today, have their origin in Flamsteed's catalog. As explained in Star Tales, these numbers do not appear explicitly in the official version of Flamsteed's catalog but in the version of it published by the French astronomer Joseph Jérôme de Lalande (1732–1807) in Éphémérides des Mouvements Célestes pour le Méridien de Paris, tome Huitième (Paris, 1783). This version contains 2,935 entries; it omits a suspicious entry without any coordinates in the constellation Lynx.

I haven't been able to find an electronic version of Flamsteed's catalog on the Web, so I have made one myself from digitized versions of Flamsteed's Historia Coelestis Britannica and Lalande's Éphémérides des Mouvements Célestes (links provided on Star Tales), and published it here in the hope that it may be useful to someone else interested in historical star catalogs.

Data available on this page

The following files are available.

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 FileName           Lrecl  Records   Explanations
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ReadMe                 80            File descriptions
flamsteed.dat         127     3046   Flamsteed's catalog
flamsteed_diffs.dat                  Differences between the Flamsteed and
                                     Lalande versions, and general remarks
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Flamsteed's Catalog

Flamsteed's catalog is contained in the file flamsteed.dat. The format of this file is described in the ReadMe file, according to the conventions for catalog descriptions of the VizieR service.

The file flamsteed.dat contains both the Flamsteed and Lalande versions of the catalog. Flamsteed-only records are flagged by a '<' character and Lalande-only records by a '>' in the first byte, so that the Flamsteed version can be obtained by running the Unix command grep -v '>' flamsteed.dat and the Lalande version by running grep -v '<' flamsteed.dat.

Flamsteed's catalog specifies Bayer designations of stars when they exist. Flamsteed also assigned 'Bayer' letters of his own to several stars. With a few exceptions, when a Bayer letter corresponds to more than one star in his catalog, Flamsteed assigns an index to the corresponding stars. For instance, 77 and 78 Tauri are marked 1 ad θ and 2 ad θ (1 near θ and 2 near θ) respectively. This feature evolved into the superscript notation used today: 77 and 78 Tauri are now called θ1 and θ2 Tauri.

I have copied the data as carefully as I could and triple-checked my work. I am confident that the file is at least very close to the originals but, human error being what it is, I cannot be perfectly sure that no error is left.

Differences

The file flamsteed_diffs.dat documents all the significant differences between the two versions, as well as other noteworthy features. Its format is more or less free-form and self-explanatory. It is not a pure ASCII file; it contains a few UTF-8 characters (degree symbol and accented letters).

When meaningful, I have indicated by (F) or (L) which of the the Flamsteed or Lalande version I found preferable. In the case of numerical differences, 'preferable' refers to the internal consistency of the data for the star (e.g., do the ecliptic coordinates correspond more closely to the equatorial ones), not correctness with respect to modern data. While Lalande has corrected some errors in Flamsteed's catalog, he has introduced others, most of them probably typos.

In order to verify ecliptic coordinates, I used an axial tilt angle of 23° 29', the value I believe Flamsteed used. Indeed, it minimizes the error between the ecliptic positions given by Flamsteed and the ones I computed from the equatorial ones. Also, as far as I could make out (my Latin being more than rusty), Flamsteed mentions this value and how he measured it as the declination of the Sun on June 10, 1690 (the summer solstice, since England was still using the Julian calendar at the time) on page 115 of the Introduction (Prolegomena) to Historia Coelestis Britannica.

Corrections

Flamsteed and Bayer designations are still in use today, but it is singularly difficult to find a complete and accurate list of all Flamsteed stars, they Bayer letter assignments, and their identifiers in modern star catalogs such as the Yale Bright Star Catalogue, the Henry Draper Catalogue, or the Hipparcos Catalogue.

Using Flamsteed's catalog as a starting point, several issues have to be considered.

  • Many entries in the catalog don't correspond to actual stars. Some result from measurement of computation errors by Flamsteed; some correspond to non-star objects (such as the planet Uranus, labeled 34 Tauri).
  • Some stars have multiple entries in the catalog. This is intentional in some cases (such as 112 Tauri and 23 Aurigae), but not in others.
  • Many of the associations of Bayer designations with Flamsteed stars are now obsolete. On one hand, the letters introduced by Flamsteed have been almost completely discarded. On the other hand, later astronomers have disagreed with some of the associations and attempted to correct them, not always in agreement with each other. In particular, Nicolas-Louis de Lacaille added 'Bayer' letters to many stars of the Southern hemisphere and entirely relettered or even redesigned some of the constellations present in Flamsteed's catalog (Argo Navis, Centaurus, Lupus).

These issues are exhaustively discussed and elucidated in Morton Wagman's book Lost Stars (McDonald & Woodward Publishing Company, Blacksburg, Virginia, 2003), which discusses stars with a Flamsteed number as well as lettered stars.

Morton Wagmans's earlier article Flamsteed's Missing Stars focuses on the Flamsteed catalog only and addresses

  • nonexistent stars,
  • stars with duplicate entries,
  • stars absent from the Bright Stars Catalog because they are too faint,
  • stars whose Flamsteed number does not appear in the Bright Stars Catalog because the constellation of their Flamsteed designation differs from the constellation to which they now belong.

Also, W. P. Bidelman's article Flamsteed stars not contained in the Yale "Catalogue of Bright Stars" provides the Henry Draper catalog numbers for the Flamsteed stars that do not have a Bright Star number.


Acknowledgment. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France.