Instruments

While constructing his system of the world and then presenting it in De revolutionibus Copernicus made use of observations of ancient astronomers and those conducted by himself. He did that in the manner developed by Ptolemy: observational material was limited to the essential minimum required to calculate the parameters of planetary models. No wonder that the basic instruments used by Copernicus, descriptions of which may be found in De revolutionibus, were copies of the ones presented in the Almagest by Ptolemy. These were: solar quadrant, used for measurement of inclination of the ecliptic in relation to the celestial equator; armillary astrolabe - the most complex instrument used in astronomy of that time, with the use of which ecliptic latitude and longitude of stars and planets could be established; parallactic instrument, with the use of which the zenith distance of a celestial body could be determined, and which was used to determine the parallax of the Moon. The triquetrum was one of the most popular astronomical instruments until the invention of the telescope, it could measure angles with a better precision than the astrolabe. Copernicus describes its use in the fourth book of the De revolutionibus orbium coelestium (1543) under the heading "Instrumenti parallactici constructio."