Saturday, February 13, 2016

Tonight's Sky for February 13: Tycho Brahe Develops his 'Tychonic' Solar System (1583)


It was on this date in 1578 that the great Danish astronomer Tycho Brahe unveiled his model of what he believed the solar system to look like, which would later come to be dubbed the 'Tychonic Model.' Never heard of the Tychonic Model? Well, don't feel bad as it is now considered a footnote in scientific history created as a compromise between the geo and heliocentric models of the solar system.

Explain, please?

In 1578, an all-out scientific debate was raging as to how the solar system worked. Since Ancient Greece, all models of the solar system were geocentric, or Earth-centered (except for that proposed by Aristarchus of Samos, which was Sun-centered). Yes, there were variances but the overall picture, namely that of the Earth being at the middle with everything else revolving around it, remained the same. This is the picture of the solar system that would hold sway for 2000 years.

In 1542, the ancient wisdom was challenged when Nicholas Copernicus published his book On the Revolutions of the Heavenly Orbs, which put forth the revolutionary, and to the Catholic Church heretical, idea that the Sun, not the Earth was at the center of the solar system. As evidence for the geocentric model were the observations that there was no woosh of air created by the Earth moving through space, objects don't land to the West when dropped, and a lack of observed stellar parallax. Going for the heliocentric model was the observation that it predicted the motions of the planets just as well as the geocentric one and the fact that it was much simpler than the geocentric model, which had grown quite complicated in order to explain retrograde motion and which the heliocentric view explained much more simply.

Then cue Tycho Brahe.

Tycho Brahe was the greatest of the pre-telescopic astronomers. Thanks to his noble birth and connections to people in high places, Brahe was able to found and fund the first modern observatory, one outfitted with large, permanently-mounted instruments and manned by a staff of trained assistants. In his 30+ year career, Brahe and his staff compiled around 10 times more observational data than all previous astronomers in recorded history combined. With a resume like that, when Brahe spoke, people listened, which is exactly what happened when he put forth his solar system model, one with the Earth at the center, the Sun revolving around the Earth, and everything else revolving around the Sun.

Ironically, rather than end the debate, the Tychonic model only served to prolong it because, when Galileo published his observations of the phases of Venus, which proved that Venus orbited the Sun, die-hard geocentrists switched allegiance from the pure geocentric to the Tychonic model because it explained the phases of Venus while still allowing for the Earth to be at the center of everything.


In the end, it would not be until the 1660s and the physics of Issac Newton that the geocentric and Tychonic models would finally be proven incorrect.

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