Caption: "Tycho's Mural Quadrant: An engraving of Tycho Brahe (1546--1601) in his Uraniborg observatory on the Swedish island of Hven, probably from the 1598 printing of his Astronomiae Instauratae Mechanica (1598), hand colored at a later unknown date." (Slightly edited.) Hven was part of Denmark in 1598 and Tycho was a great Dane.

Features:

1. Tycho---he's one of those historic people known by their first names (like Michelangelo (1475--1564), Galileo (1564--1642), and Ann Margret (1941--))---was the greatest pre-telescopic observational astronomer.

2. A mural quadrant is a quarter of a divided circle. It is built into a wall and aligned with the celestial meridian. Measurements of time and altitude of transits of astronomical objects with a mural quadrant can be converted without painful spherical trigonometry into equatorial coordinates (i.e., right ascension (RA) and declination (Dec or δ)). Very accurate measurements are possible with large, accurately-made mural quadrants such as Tycho's.

3. In astronomical observations, Tycho's angular positions had errors of order 1 arcminute ('). To be more precise, typically his errors were 1' to 3' and transcription errors were sometimes much larger. Tycho himself aspired to 1 arcminute accuracy. See Wikipedia: Tycho Brahe: Observational astronomy.

   Modern professional astronomy typically can reach arcminute accuracy from the ground and with adaptive optices can reach accuracies as small as tens of milliarcminutes (see Wikipedia: Adaptive optics: Wavefront sensing and correction).

4. The quality and quantity of his observations of astronomical objects (stars and planets) surpassed any achieved before and formed the basis of the Tycho's goal of renovation of astronomy.

   Actually, the Ottoman Turk polymath Taqi ad-Din (1526--1585) may have made astronomical observations of comparable accuracy to Tycho's just a bit earlier in history, but that data seems to have had little importance to the later development of astronomy.

5. Tycho was lucky that Johannes Kepler (1571--1630) managed to get a hold of his data---Tycho's unastronomical heirs would have hidden it away---like the dog in the manger---until it was worthless.

6. Tycho first became famous in his lifetime by his observations of and reports on the supernova SN 1572 (AKA Tycho) and the Great Comet of 1577.

   These reports proved---although it took decades and a lot of other evidence for full acceptance---that Aristotelian cosmology was wrong and the Heavens were NOT changeless and comets were astro-bodies and NOT weather phenomena.

7. The Great Comet of 1577 was particularly useful in proving that the celestial spheres of Aristotelian cosmology did NOT exist.

   By the by, the Great Comet of 1577 is NOT Halley's comet nor famous from any other visit to the inner Solar System. It's orbital elements are mostly unknown (see JPL Small-Body Database Browser: Comet 1577 V1).