How Halley’s Comet Shaped History
Bayeux Tapestry. Credit: Public Domain

How Halley’s Comet Shaped History

05/04/2017Written by Robbie Bosley

Halley’s Comet, innocuous as it is today, has historically inspired many key invasions.

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Halley's Comet in 1986. Credit: NASA/W. Liller

As any historian will tell you, the smallest detail can dramatically change the course of history. Such is the case with Halley’s Comet, whose recurring appearances may have inspired many significant turning points in human history.

Halley’s Comet orbits the Sun once every 75-76 years, and may have done so for the past 200,000 years, giving humans many chances to see it and ascribe special ‘divine’ significance to its appearance long before English astronomer Edmond Halley predicted in 1705 that it was just a small body periodically orbiting the Solar System.

The Fall of Rome

The Fall of Rome
Halley's Comet in 1759. Credit: Public Domain

Cosmic portents of doom were all too apparent in the 5th century. Reports in the 440s describe a lunar eclipse, whereby the Earth casts a reddish shadow over the moon; the Northern Lights were seen much further south than usual; and to cap it all off, in June 451 a red point of light appeared with a fearsome tail streaming behind it – Halley’s Comet.

Within 3 weeks, Attila the Hun invaded Roman France, and the Roman world trembled before him. He was nicknamed the ‘Scourge of God,’ and many Christian theologians at the time thought that he was sent by God as an instrument of destruction against sinners. Earlier in the 440s, a solar eclipse had turned the Sun black, and the subsequent lunar eclipse turned the Moon red ‘like blood’. The sighting of strange and mysterious events in the sky, including Halley’s Comet, only added to the aura of terror surrounding Attila.

Though Attila would be repulsed at the Battle of the Catalaunian Plains by the Romans and Visigoths, the damage done by this invasion was immense. The Visigoths fled into Spain, and Western Rome would not survive the century.

The Norman Invasion

The Norman Invasion
Bayeux Tapestry showing Halley's Comet in 1066. Credit: Public Domain

Halley’s Comet made an appearance before another significant battle – Hastings. William of Jumièges, a Norman monk, described it as having a ‘three-forked tail’, and suggested that it ‘portended, as many said, a change in some kingdom’. When it first appeared over England and Normandy in April 1066, Duke William of Normandy is said to have remarked ‘It is a wonderful sign from Heaven’. He already had the Pope’s backing to invade England, and this sign assured him that God would back his claim to the English throne.

In September 1066, the English king Harold Godwinson marched his army north to Yorkshire, where he defeated the invading Norwegian king Harald Hardrada at the Battle of Stamford Bridge. He then rushed south to meet the Normans, who had just landed near Hastings.

Harold was killed in the battle, probably by an arrow to the eye, and William of Normandy became William I of England. This marked the end of Anglo-Saxon dominion over England and the beginning of Norman rule over the English.

Inspiring an Empire

Inspiring an Empire
Halley's Comet (684 AD) depicted in the Nuremberg Chronicle in 1493.

In 1222, Halley’s Comet once again made a flyby, with perhaps the most devastating effect in its history. The Great Khan Temujin, known to the west as Genghis Khan, supposedly took the comet as his own personal star. He reasoned that its westward trajectory was a sign that he should focus his conquests westward.

While Temujin himself would die just five years later, his ancestors went on to invade and conquer parts of Poland, western Russia, Hungary and Bulgaria, slaughtering millions along the way. The resulting Mongol Empire was the largest empire in all of history, stretching from Poland to the Chinese coast.

Modern Halley

Modern Halley
Halley's Comet imaged by ESA's Giotto probe. Credit: NASA/ESA/Giotto Project

We now know much more about Halley’s Comet. It is made up of ‘dirty ice’, which includes ice, frozen carbon oxides, ammonia, as well as dark dust.

When it nears the Sun, the ice sublimes from the surface, turning straight from a solid to a gas, which produces the bright tail of the comet. The actual comet itself is not bright at all, but is very dark owing to the dust contained within.

Halley’s Comet was last seen in 1986, meaning that it won’t be visible again until 2061. Who knows what change in history the next appearance will bring us?

About the Author: Robbie Bosley is a current physics student at the University of Leicester and works at the National Space Centre as a Science Interpreter.