The first great optical observer. His primary contribution to astrophysics was the precise data he collected on the motions of the celestial bodies. His data were accurate to within 1/60 of one degree, i.e., to within 1 arc minute. (Comment--A simple thing which Tycho did which greatly improved his accuracy was to make several measurments of quantities and to then average his results in order to arrive at his final answer. This is standard practice today, but was highly unusual during Tycho's time.)
The data were accurate enough to allow people to rule out theories of the motions of the celestial bodies. The result of his (and other people's) studies was to show that neither the Ptolemaic nor the Copernican models were acceptable. Both models were not consistent with the data!!!
This was the first step toward the development of an understanding of the Solar System.
Oh, and like all observers, he also proposed his own model.
beyond Moon (no parallax) ===> heavens were not immutable
