NHAS - Today in Astronomy History

	1473	Polish astronomer Nicolaus Copernicus born. He was the first to present convincing arguments that the Earth orbited the Sun and not the other way around. Existing Ptolemaic theory held that the Moon and Sun orbited the motionless Earth, and that Mars, Jupiter, and Saturn were situated beyond the Sun (Uranus, Neptune, and Pluto had not yet been discovered). The problem was with Venus and Mercury. Ptolemy placed them closest to the Sun while other astronomers held that they were beyond the Sun. Copernicus realized that neither situation explained their motions correctly, and the only thing that did was if the Sun were motionless with all the planets, including the Earth orbiting it. This was considered heresy as it placed the imperfect and changeable Earth amongst the perfect and unchanging heavens. For this reason, publication of the theory was delayed 36 years, until 1543, the year of his death.
	1986	Russia launches the core module, the first component of the Mir space station.