nova stella

A poet of Shakespeare's time was apt to say that his love for his beloved was not "sublunar." He meant that his affection was like the stars–constant and unchanging. According to the philosophy that prevailed in Shakespeare's time, change occurred only below the Moon, in our terrestrial world of jumbled elements and inconstant emotions. By contrast, the celestial realm above the Moon, like the poet's love, was fixed and eternal. Or so people believed. And then, to the consternation of poets and philosophers, in the autumn of 1572 a new star blazed in the constellation Cassiopeia. The star was well placed for viewing, high overhead in the evening sky. It was brighter than any other star, bright enough to be seen in broad daylight. All Europe was agog. But was this new star really above the Moon, in which case philosophers were wrong and the heavens do change?

. . . On the evening of November 11, 1572, Tycho was walking home to supper when he happened to glance up at the stars above his head. He saw the new star at once, the nova stella. Afraid to believe his own eyes, he asked his servants and neighbors to look into the sky and describe what they saw. They confirmed his observation. The star was real. Tycho was a talented astronomer, and he had recently built a fine new instrument (not a telescope; that device was still a few decades away) for determining the positions of stars. Carefully, he measured the angular separation of the new star from the stars of Cassiopeia. He continued these observations at different times of the night and throughout the winter as the star slowly faded. He also collected measured positions of the new star from other European observers. He was trying to determine the star's parallax, the apparent change in the position of an object when viewed from two different places . . . The object in Cassiopeia did not shift at all against the background stars when viewed from different places. From these observations Tycho knew that the new star was in the highest heavens, far beyond the Moon. The philosophers were wrong; the heavens do change.

-- Chet Raymo An Intimate Look at the Night Sky

Tycho Brahe (a father of modern astronomy)