He observed the great comet that was visible in the Northern sky from November 1577 to January 1578. Within Lutheranism, it was commonly believed that celestial objects like comets were powerful portents, announcing the coming apocalypse, and in addition to Tycho's observations several Danish amateur astronomers observed the object and published prophesies of impending doom. He was able to determine that the comet's distance to Earth was much greater than the distance of the Moon, so that the comet could not have originated in the "earthly sphere", confirming his prior anti-Aristotelian conclusions about the fixed nature of the sky beyond the Moon. He also realized that the comet's tail was always pointing away from the Sun. He calculated its diameter, mass, and the length of its tail, and speculated about the material it was made of. At this point, he had not yet broken with Copernican theory, and observing the comet inspired him to try to develop an alternative Copernican model in which the Earth was immobile. The second half of his manuscript about the comet dealt with the astrological and apocalyptic aspects of the comet, and he rejected the prophesies of his competitors; instead, making his own predictions of dire political events in the near future. Among his predictions was bloodshed in Moscow and the imminent fall of Ivan the Terrible by 1583.