Halley’s Comet – named for Sir Edmond Halley, the English bloke who used Newton’s new art of calculus to surmise that frequently seen comets in history were, in fact the same comet – returns to the inner solar system once every 76 years or so, on average.  When this occurs, it is usually quite visible with the naked eye for weeks at a time.
76 years is quite a short period for a comet that can be so easily seen. It is the only one that can be seen twice in a single human lifetime.
Alas, the only appearance during my lifetime – in 1986 – was far less than spectacular. Earth’s and Halley’s orbits were sort of “out of synch” and thus minimized earth’s view of the comet when it was brightest. I was most disappointed, since I had read about it so much and had been very let down by the “flame out” of Kahoutek in 1973-74.
Such has not always been the case.
In 1066 the Comet portended the defeat of English King Harold II to William, the conqueror from Normandy at a battlefield near Hastings. [2A] So important was this astronomical sign that its significance and image are captured on the magnificent 70 meter (230 feet) long tapestry that that tells the story of conquest, and still survives in Bayeux, Normandy. [2B]
Over the millennia, many other occasions of Halley’s return and sighting have been recorded in several cultures. As there was no effective difference between astronomy and astrology, a comet’s appearance (exceedingly rare as they are) are usually associated with some momentous decision, or a historical event.
Could that event be the end of the world?
The year was 1910, and the comet’s return was certainly expected. Based on its path through the solar system since its 1835 appearance, astronomers and physicists predicted it would appear in spring. 
And yet, in January, a comet brighter than anything anyone had expected appeared! Was this Halley’s? Appearing early? Astrophysicists re-worked and labored over their calculations again. As they did, the comet got so bright it was visible during the day! It’s brightness rivaled that of famously bright evening and morning “stars” – Venus and Jupiter – but with a tail painted across the sky.
Soon enough scientists announced: No! This is not Halley’s. This is an unrecorded comet, probably with a period of 50,000 to 100,000 years! People alive then were fortunate to see such a spectacle. That 1910 comet is often referred to as “The Daylight Comet.”
Historians regularly call 1910 “The Year of Two Comets.” Just a few months after the Daylight Comet faded away Halley’s made its scheduled appearance in April.
Astronomers first sighted it in early April, and it could be seen with the naked eye starting around April 10. They tracked it, and – again – many scientists and astronomers made their calculations and observations. Those who calculate did their calculations: Each orbit of a comet is different, and everyone wanted to know how bright the comet would get, and how close it would get to earth.
On April 20 the comet reached perihelion – its closest approach to the sun – and became very easily viewable from earth with casual unaided observation. [On cue, Mark Twain passed away]. After perihelion they predicted an Earth-comet approach so close that on May 18th Earth would pass through the comet’s tail. Now that’s astonishing!
What would happen then? How should this news be treated? Should they let everyone, and anyone, know? Would panic and hysteria ensue? What about the news that spectroscopic surveys of the tail suggested the tail was comprised of a high percentage of cyanogen, a precursor to cyanide?
A few scientists suggested that this could make the entire atmosphere fatally toxic! But most scientists thought that there was no danger. Yet, we couldn’t know until we actually passed through.
What do you do when the world might end? Many people just stayed home, preferring to spend their final hours with their families. Factories shut down for want of workers. Yet, in many places around the world the answer was: have a party. A big party. Get all your friends, family, food and booze together and enjoy yourselves like there might be no tomorrow. Humans around the world wondered what might happen, … while partying. It was a delicious time: while the vast majority had little or no fear of the “calamity”, they took it as an opportunity to have a good time, enjoy this singular event: a few spectacular hours of passage. And by doing so – maybe – mocking those who were in hysteria.
It might have been the last time until now (the SARS-CoV-2 pandemic, March 2020) that the world has been more or less united in the same activities. Mankind united by a single set of events.
Earth passed through the tail of Halley’s Comet. When it was over, of course, nothing happened. They had simply witnessed and experienced an event that probably no other human had! And no other human will for a very long time. 
Well, perhaps more than that happened. Quite a few probably had hangovers – and there might have been a mini-baby boom in early 1911. (There was, in fact, a few percent jump in US births in 1911 over 1910; however, (1) that was a time of such massive immigration; and (2) birth numbers jumped consistently from 1900 until 1918 [insert WW1 comment here], so it’s not clear what we should attribute this mini-baby boom to.) 
Anyhow, one way or the other, this SARS-CoV-2 thing (and the illness it causes, COVID-19) will pass. Some of us have panicked. Nearly all of us will survive, although many of us will be changed; maybe with larger waistlines.
Unlike extraordinary 1910 – with two brilliant comets, and with Halley’s extremely close-approach to Earth – an epidemic or pandemic will occur again. For some of us, perhaps, within our lifetime. What will happen next time? Much will depend on what we have learned. And what we remember.
I hope it’s not the end of the world. But in any case, we can have a party.
By the way: Halley’s is predicted to appear again in the summer of 2061. I don’t think I’ll hang around for that one. Gotta join ol’ Mark Twain sometime. But if I do make it to then: we’re having a heck of a party!
Until next time, I wish you peace and health
Joe Girard © 2020
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 Halley’s orbital period varies a bit with every orbit; and the variation is random. Why? A) The comet sheds a fraction of its mass with each inner solar system pass due to solar heating; and B) the comet is tiny and light, and thus subject to (usually) slight gravitational perturbation by planets. Halley’s once had an orbital period of many tens of thousands of years, falling from the Kuiper Belt – or more likely the Oort Cloud – but after repeated close encounters with planets, it has been captured and now strays only about as far away from the sun as the 8th planet Neptune at aphelion – it’s farthest distance from the sun.
[2A] My son Aaron and I walked the battlefield in April, 2010. It is actually quite far inland from Hastings. There is a lovely town there now, with a beautiful Abbey. The town is called, appropriately enough: “Battle”
[2B] My wife and I were fortunate enough to have time to walk along and see the entire tapestry during our Normandy tour, in May, 2018.
 Mark Twain was born in 1835, with Halley’s Comet visible in the night sky. As he aged, he grew weary and bitter – he had lost his fortune, three of his four children perished before him, and then his wife went. In such a dark cloud he predicted his own demise in 1910, concurrent with Halley’s reappearance. He was correct.
 US Live Birth Statistics https://www.cdc.gov/nchs/data/statab/t1x0197.pdf
 Deaths from Halley’s. There were quite a few deaths associated with Halley’s, almost all of them due to the hysteria. I read a report of a 16-year old Canadian girl falling to her death from the roof of a building where an “end of the world” party was being held.
 Author’s note: My disappointment with Halley’s 1986 appearance was greatly relieved by Hale-Bopp in March and April, of 1997. On a spring break trip to the Arizona desert, with perfect viewing, Hale-Bopp was magnificent. And its brightest night was almost exactly the same as a lunar eclipse and – right next to the moon – Mars in perfect and brilliant opposition.