Tycho Brahe (1546-1601) The first great observational optical astronomer. His primary contributions to astrophysics were the design and development of observing instruments and the precise data he collected on the motions of the celestial bodies in the pre-telescope era. At left is shown Tycho's Great Mural Quadrant . Tycho's mural ("wall") quadrant was a 90o arc of radius 2 meters attached to a north-south wall with a sighting tool to allow an observer to measure the altitudes of celestial objects as they passed through the Celestial Meridian . The observer stood near the arc and sighted the celestial objects through a slot on the far wall, noting the altitude of the object when it was due south, that is, when it was crossing the Celestial Meridian. Tycho's data were reputed to be accurate to nearly an arc minute. Before his time, the accuracy was on the order of one-fourth of a degree, around ten times worse. In contrast to earlier observers, Tycho observed objects throughout their cycles rather only at particular times, such as opposition and quadrature. To the right is a more modern transit instrument built in 1885 (Fauth), the Chabot Space & Science Center's meridian transit telescope in Oakland, California.

The data were complete and 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 geo-centric model for planetary motion.

Other Accomplishments

• SN1572 (Tycho's SN) -- Found no parallax for SN1572 ==> distant. Tycho noted that the heavens (stars) were not unchanging!
• Comet (1577) -- Comet was farther away than the Moon, based on the Comet's parallax contradicting the work of Aritotle who thought comets were atmospheric phenomena.
• Determination of the 23.5^o tilt of the Earth's rotation axis
• No measured annual trigonometric parallax for the stars, the closet star Proxima Centauri has a parallax angle of less than 1/60-th of an arc minute!