The Accuracy of Tycho Brahe's Instruments

Thoren V. E. , “New Light on Tycho's Instruments”, Journal for the history of astronomy , iv (1973), 25–45.

Brahe Tycho , Astronomiae instauratae mechanica (Nurenberg, 1602). This work has been reprinted as vol. v of Tychonis Brahe opera omnia (edited by Dreyer J. L. E. , 15 volumes, Copenhagen, 1913–29), and published in an English translation by Hans Raeder and others as Tycho Brahe's description of his instruments and scientific work (Copenhagen 1946).

For example, on p. 19 of Tycho Brahe's description (ref. 2) one finds: “Only this I wish to state here with regard to this instrument and to the others, namely, that all of it has to be as nearly perfect as is possible in every respect and that, therefore, one should employ skilful craftsmen, who know how to carry out this sort of work artfully, or else can learn how to do it. And even if they cannot perhaps do it all perfectly the first time, the constructor must not let him self be discouraged, but have the work repeated and improve the defects in every way, until none is left…. Consequently we have remade most of the instruments described in this book more than once, not without great expense”.

Delambre J. , Histoire de l'astronomie moderne (Paris, 1821), i, 179.

Lalande J. , Astronomie (Paris, 1792), ii, 566.

Woldstedt F. , De gradu praecisionis positionum cometae , 1577 (Helsingfors, 1844).

Peters C. , “Bestimmung der Bahn des Kometen von 1585”, Astronomische Nachrichten , xxix (1849), 209 et seq.

Argelander , “Uber den neuen Stern von Jahre 1572”, Astronomische Nachrichten , lxii (1864), 273–6.

Dreyer J. , Tycho Brahe (Edinburgh, 1890), 387. Dreyer also includes a brief critique of work of Woldstedt, Peters and Argelander on pp. 356–7.

Tupman G. , “A Comparison of Tycho Brahe's Meridian Observations of the Sun with Leverrier's Solar Tables”, The observatory , xxiii (1900), 132–5, 165–71. There is an interesting note on Tupman's paper by Dreyer in The observatory , xxiii (1900), 211–12.

The observational logs constitute vols x-xiii of Tychonis Brahe opera omnia (ref. 2).

A good modern discussion of the calculation of changes in stellar positions, including formulae suitable for computer work, can be found in Eichhorn H. , Astronomy of star positions (New York, 1974).

For example the average low temperature for Copenhagen in January is −2°C, which leads to a refraction correction of 50′·5 for stars with an altitude of 50°; for the same star the mean refraction is 48′·6, a difference of about 2′. Likewise the average high temperature in July is 20°C; for the same star the corresponding refraction correction is 46′·9, again a difference of some 2′.

Standard deviations were only calculated in those cases where there were at least eight measurements.

A brief history of the idea that Tycho was careless in orienting his instruments is given by Dreyer in Tycho Brahe , 358–60. On pp. 388–9 he considers a set of azimuths measured in 1582 and shows that their accuracy precludes any such misalignment. A recent reference to Tycho's misaligned meridian is on p. 6 of Forbes's E. G. Greenwich Observatory , i (London, 1975).

Curtz Albert , Historia coelestis (Augsburg, 1666). Dreyer in Tycho Brahe , 371–3, gives a critique of this book, concluding that “The Historia coelestis gives the reader a fair idea of the general scope of Tycho's work, but it cannot be used for any scientific purpose”.

For example Tupman says that there were no useful solar observations made with the revolving wooden quadrant for 1589. A brief survey of the 1589 entries in vol. xi of the Opera omnia indicates that there were 64 meridian altitudes of the Sun taken with that instrument. It is also clear that for other years he was using incomplete data. Whether including this missing data would change his results is unclear.

See ref. 1 for a chronology of Tycho's instruments.