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In late antiquity and throughout the middle ages, the positions of stars on the celestial sphere were obtained from the star catalogue of Ptolemaios. A catalogue based on new measurements appeared in 1437, with positions by Ulugh Beg, and magnitudes from the 10th-century astronomer al-Sufi. We provide machine-readable versions of these two star catalogues, based on the editions by Toomer (1998, Ptolemy's Almagest, 2nd edn.) and Knobel (1917, Ulugh Beg's catalogue of stars), and determine their accuracies by comparison with the modern Hipparcos Catalogue. The magnitudes in the catalogues correlate well with modern visual magnitudes; the indication "faint" by Ptolemaios is found to correspond to his magnitudes 5 and 6. Gaussian fits to the error distributions in longitude/latitude give widths σ 27 /23 in the range |Δλ, Δβ| < 50 for Ptolemaios and σ 22 /18 in Ulugh Beg. Fits to the range |Δλ, Δβ| < 100 gives 10−15% larger widths, showing that the error distributions are broader than Gaussians. The fraction of stars with positions wrong by more than 150 is about 2% for Ptolemaios and 0.1% in Ulugh Beg; the numbers of unidentified stars are 1 in Ptolemaios and 3 in Ulugh Beg. These numbers testify to the excellent quality of both star catalogues (as edited by Toomer and Knobel).

Tycho Brahe completed his catalogue with the positions and magnitudes of 1004 fixed stars in 1598. This catalogue circulated in manuscript form. Brahe edited a shorter version with 777 stars, printed in 1602, and Kepler edited the full catalogue of 1004 stars, printed in 1627. We provide machine-readable versions of the three versions of the catalogue, describe the differences between them and briefly discuss their accuracy on the basis of comparison with modern data from the Hipparcos Catalogue. We also compare our results with earlier analyses by Dreyer (1916, Tychonis Brahe Dani Scripta Astronomica, Vol. II) and Rawlins (1993, DIO, 3, 1), finding good overall agreement. The magnitudes given by Brahe correlate well with modern values, his longitudes and latitudes have error distributions with widths of 2 , with excess numbers of stars with larger errors (as compared to Gaussian distributions), in particular for the faintest stars. Errors in positions larger than 10 , which comprise about 15% of the entries, are likely due to computing or copying errors.