---
title: "History of the extraterrestrial life debate"
chunk: 3/4
source: "https://en.wikipedia.org/wiki/History_of_the_extraterrestrial_life_debate"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T04:31:38.469760+00:00"
instance: "kb-cron"
---

Nicolaus Copernicus published De revolutionibus orbium coelestium in 1543, kickstarting the Copernican Revolution. This book restored and updated the old idea of Aristarchus that Earth spins around the sun. The new version was written with so much mathematical detail that it could contest the Ptolemaic model. By this time, scientists noticed several inaccuracies in the Ptolemaic model. They were more open to revising it, but largely kept using it because of the huge work involved in changing the tables. Copernicus thought that Earth spinning around the sun could provide a simpler explanation for the retrograde motion of the planets, and calculated the distance of the planets to the Sun. However, he kept the idea of circular orbits, and added several composite orbits to explain the errors caused by it. Although he correctly displaced the center of the Solar System, this first model turned out to be as inaccurate and as complex as the Ptolematic one, and did not get much supporters in the first decades.
A recurring problem for both models was the lack of quality data, as the telescope had not been invented yet and naked eye observations are highly inaccurate. The Danish Tycho Brahe sought to gather such data, by creating huge naked-eye observatories. On his deathbed, he asked his assistant Johannes Kepler to make sense of his observations, so that it did not feel like he lived in vain. Kepler initially kept the circular orbits, and eventually found a system that would explain all the data, except for a mistake of 8 arcminutes on the position of Mars. However, Kepler trusted the accuracy of Tycho's observations, and so refused his provisional results. Instead, he challenged the circular orbits and tried with other shapes. With orbits shaped as ellipses he could explain the recorded motion of all the planets, including Mars' retrograde motion, without using composite circles to do so. He compiled his final results as the Kepler's laws of planetary motion.