Before Tycho settled at Hveen he had never regularly observed the sun,[1] but (as we have already mentioned) from his birthday, the 14th December 1576, he took regular observations of the meridian altitude of the sun, and later, when his stock of instruments increased, several quadrants were simultaneously employed for this purpose. Above all, he employed from March 1582 the great mural quadrant for observing the sun on the meridian, while the declination was also very frequently measured with the armillæ. These observations were made with the object of improving the theory of the sun's apparent motion. The equinoxes of the years 1584–88 were carefully determined, but owing to the difficulty of fixing the moment of solstice on account of the very slow change of declination at maximum and minimum, he did not make use of the solstices to find the position of the apogee and the amount of the excentricity of the orbit, but determined the time when the sun was 45° from the equinoxes, in the centre of the signs of Taurus and Leo. Copernicus had followed the same plan, but had made use of the signs of Scorpio and Aquarius, while Tycho objected to these that the sun was too low in the sky, and the influence of refraction and parallax too great. He found the longitude of the apogee = 95° 30′, with an annual motion of 45″ (should be 61″, Copernicus had only found 24″), and the excentricity of the solar orbit = 0.03584, the greatest equation of centre being 2° 314′. In the determination of the apogee he was more successful than Copernicus; but while the latter made the equation of the centre too small, Tycho made it too great. The length of the tropical year he found by combining some observations by Walther (reduced anew after determining the latitude of Nürnberg) with his own to be equal to 365d 5h 48m 45s, only about a second two small. With his new
- ↑ Only in 1574 he had at Heridsvad observed the meridian altitude of the sun on seven days in March and on two days in May.
