All sources

Magnitudes of Thirty-six of the Minor Planets for the First Day of each Month of the Year 1857

Norman R. Pogson. Monthly Notices of the Royal Astronomical Society 17(1), 1856, 12-15.

Verification

Tier A Author, title, publisher and year checked against a publisher record, catalogue or scan. Entries may cite this.

Reliability

primary-source

Kind

article

Identifiers

• doi:10.1093/mnras/17.1.12
• publisher or record page

Accessed

2026-07-31

The original source of what is now called Pogson's ratio, 2.512, the fifth root of 100. Bibliographic details (MNRAS vol. 17, issue 1, pp. 12-15, 14 November 1856) verified against the Oxford Academic publisher record for the article and against ADS bibcode 1856MNRAS..17...12P. The DOI resolves to the same OUP page. Read in full from the ADS scan (not a summary): the paper is mainly a table of predicted opposition magnitudes for 36 minor planets for 1857, used to avoid mistaking a nearby star for the object sought. The magnitude scale is introduced only in passing, to explain how the table's monthly columns were computed: "calculated on the assumed ratio of the light of 2.512, i.e. that a star of any magnitude, as for instance the eighth, contains 2.512 times the light of the next less, or ninth magnitude" (p. 13). Pogson goes on to explain the choice (p. 14): earlier observers had derived ratios scattered between about 2.4 and 2.83 (Dawes' 4, Johnson's 2.43, his own independent mean of 2.4, Steinheil's 2.83, Stampfer's 2.519), and among these "it signifies little which... is adopted"; he "selected 2.512 for convenience of calculation," because it is the value whose reciprocal of one-half its logarithm is exactly 5: in modern terms, the ratio whose fifth power is exactly 100. He does not use the word "magnitude scale" as a named system; that framing, and the name "Pogson's ratio," are later usage. This passage was verified against the page image itself (300 dpi scan), not the OCR text layer, because the OCR renders the key fraction ambiguously.