Flamsteed numbers –
where they really came from
FLAMSTEED NUMBERS are the numerals attached to stars in a constellation for identification purposes, such as 61 Cygni or 51 Pegasi. They are named after the English Astronomer Royal John Flamsteed (1646–1719), who produced the first major star catalogue made with the aid of a telescope, published posthumously in 1725. It is often assumed that the so-called Flamsteed numbers were assigned to the stars by Flamsteed himself, but that is not the case. Flamsteed’s published catalogue contained no such numbering system. So where did they come from?

The American historian Deborah Jean Warner seems to have been the first to point out that the numbers we now use were actually allocated by a French astronomer, Joseph Jérôme de Lalande (1782–1807). They appeared in a revised edition of Flamsteed’s catalogue published in 1783 in a French almanac, Éphémérides des mouvemens célestes. In this French edition, Lalande numbered Flamsteed’s stars consecutively by constellation. This is the numbering system we now know as “Flamsteed numbers”. The illustration below shows an example from the first page of Lalande’s edition. Click on it for an enlargement.

The German astronomy historian Wolfgang Steinicke has noted that Johann Bode anticipated Lalande by introducing a column headed “No. nach Flamsteed” (i.e. “number according to Flamsteed”) in a list of the 280 brightest stars in the Astronomisches Jahrbuch for 1781 (published 1778), but this was not the entire catalogue; what’s more, the stars are listed in order of right ascension and not by constellation so the numbers do not appear sequentially as they do in Lalande’s version.

Although there were no Flamsteed numbers in Flamsteed’s own catalogue, Flamsteed did include columns noting the order of appearance of each star in the catalogues of Ptolemy (the Almagest) and Tycho Brahe, plus a third column with the Greek letters assigned by Johann Bayer (the so-called Bayer letters). These columns were repeated by Lalande in his French edition. In the example below, the abbreviation “inf” in the Ptolemy column refers to the so-called informatae, or unformed, stars that Ptolemy regarded as lying outside the constellation figure proper. The star referred to here is the one we know as Alpha Arietis, the brightest star in the modern Aries. Despite its brightness, Ptolemy decided it did not fit the constellation figure. Instead, he placed it among the informatae.

lalande_ephemerides.jpg

Above: The first page of J. J. Lalande’s edited and corrected version of John Flamsteed’s star catalogue, published in 1783. The stars shown here belong to the constellation Aries. In the first column, Lalande numbered each star consecutively by constellation. These are the numbers that we now call Flamsteed numbers. There was no such column in Flamsteed’s original catalogue. Click on the illustration for an enlargement of the page, or click here to see the whole of Lalande’s edited catalogue.