Ruining perfection
Many ancient cultures saw comets as harbingers of doom and disaster. The predictable motions of the planets, the Sun, and the Moon, as well as the seasonally changing constellations, were reassuring in a chaotic world. A comet’s sudden appearance shattered this order.
Aristotle described Earth and the sky as fundamentally different spheres. The terrestrial sphere was ever-changing and corruptible. Beyond lay the realm of perfection where the Sun, the Moon, and planets rotated on incorruptible crystalline spheres. It seemed inconceivable that a random disruption could pass through this realm of perfection. So, to explain this corruption, Aristotle suggested that comets were vapors that rose from Earth and ignited in the upper atmosphere. Astronomers ultimately rejected Aristotle’s explanation, but his views held sway in Western philosophy for more than 1,500 years.
Westerners weren’t alone in these beliefs, either. Chinese astronomers called comets “bushy stars” (bèi xīng) if they had no tail, or “broom stars” (huìxīng) if they had one. Ancient Chinese records of comet observations were the most extensive and accurate of both the ancient and medieval periods. Yet they too saw these visitors as disastrous omens.
Signs and Omens
Comets were viewed as disruptors of a perfect cosmic routine. As Carl Sagan said, a comet’s appearance was “assured of some tragedy for which it can be held accountable.” Halley’s Comet made an easy scapegoat over the centuries, each time it returned to the sky.
1066: The cosmic visitor was viewed as a bad omen for the Anglo-Saxons’ kingdom, then ruled by Harold II. A month after William of Normandy invaded, the king died at the Battle of Hastings. The Bayeux Tapestry, which recorded the conquest, depicts the first-known illustration of Halley’s Comet.
1301: Halley’s Comet once again graced the heavens. A few years later, Italian artist Giotto di Bondone painted The Adoration of the Magi. Art historians believe this was Comet Halley as Giotto remembered it — a rare example of Halley’s comet being viewed as a blessing.
1456: The last vestige of the Roman Empire vanished when the Ottomans captured Constantinople in 1453. Europe was awaiting a full-scale invasion from the Turkish army when Comet Halley reappeared in 1456, fueling panic and despair. By some reports, Pope Calixtus III ordered church bells to be rung every day at noon for intercession against the comet’s influence.
Eventually, a Danish nobleman would defy superstition and overthrow Aristotle’s lingering ideas. And this end was heralded by a bang.
In November 1572, a “new” star — today we know that star was a supernova — appeared in the constellation Cassiopeia. The young Tycho Brahe was one of the first to make detailed measurements of this event. Brahe could not detect any parallax for the star, which would have been measurable if the object was atmospheric. Brahe’s conclusion was simple: The new star was in heaven itself, within the so-called eighth sphere, the realm of immutability. To those who doubted his findings, he said, “O coecos coeli spectatores,” which roughly translates to “O blind spectators of heaven.”
Five years later, Brahe tested his theory on a newly visible comet. He was now equipped with a private observatory filled with instruments of his own design. Telescopes were still decades away, but he could measure the comet’s course and position with great accuracy. As with the new star of 1572, he found no parallax, placing the comet among the realm of planets. His findings were not accepted by many of his contemporaries, including Johannes Kepler and later Galileo Galilei. Even Brahe himself could not completely shake off the bonds of astrology, making predictions about the comet’s influence on Earth. Nevertheless, Aristotle’s crystalline spheres were soon abandoned.
By the mid-17th century, the Age of Enlightenment was in full bloom. Brahe’s observational work on comets and Kepler’s laws of planetary motion provided novel tools for a new generation of astronomers. Among them was a young man named Edmond Halley.