ISTI MIRANT STELLAM

The Bayeux Tapestry is nearly 1000 years old. Assaulted by time, wars, vandals, fires, air, strontium 90 and sunlight, it is a wonder it has survived.

In that time, Comet Halley has flown near the Earth, around the Sun, and back out into deep space thirteen times in a highly eccentric elliptical orbit.

Astronomers did not know what a comet was or how it behaved until Isaac Newton's discoveries. His friend, the second Astronomer Royal Edmond Halley, used Newton's ideas and was the first to accurately predict the return of a comet, which is the most famous of all comets because of his prediction. The comet returned just when he said it would, but Halley had been dead for many years when it did. Before Halley, educated people assumed the appearance of a comet meant the death or the birth of kings, or the loss or victory of battles. (A few witty people pointed out that comets always seemed to predict everything, anything, or nothing in particular.)

But even to the eye of a modern educated person, the appearance of a large comet in the night sky is a deeply troubling, worrisome sight. Something deep in your mind tells you: The sky is broken.

The average time between appearances of Comet Halley is 76.3 years. (See earlier post about Halley and Tsar Peter the Great getting drunk and pushing each other around in a wheelbarrow at the Old Royal Observatory at Greenwich.)

Differences between returns of the comet are caused by random approaches to the great gas giant planets Jupiter, Saturn and Uranus -- whether these planets are there or on the far side of the Sun as the comet passes. Their massive gravitational effects speed the comet up or slow the comet down.

I saw it above the Australian desert in April 1986, thrilling for me, but one of the poorer historical flybys. The 1910 flyby was spectacularly close, clearly visible all over the world, skimming the atmosphere with cyanide molecules, causing unnecessary tabloid headline panic. Your next chance to see it will be in 2062. (Be careful when you cross the street and eat your vegetables if you want to see it.)

Counting back:

1986.33 1910.03 1833.73 1757.43 1681.13
1604.83 1528.53 1452.23 1375.93 1299.63
1223.33 1147.03 1070.73

... which is within four years -- well within the gas giant irregularities -- of the Battle of Hastings in 1066, which the victor's Queen Mathilde immortalized in the Bayeux Tapestry.

Scroll down from this link to see a fine detail of the Bayeux' comet with tail prominent, as it looked to Mathilde's unaided eyes in 1066.

At the far right of Panel 15, astrologers stare up at what is believed to be Comet Halley and predict the fall of the Saxon King Harold, and the conquest of William of Normandy. The legend reads ISTI MIRANT STELLAM -- "These men gaze at the star."