Halley's Comet is arguably one of the most famous comets, being a "periodic" space rock that graces the Earth with its presence every 76 years. This means that it's possible for a person to see the comet once or, if they're lucky, twice in their lifetime. The last time Halley was seen was in 1986, meaning it is projected to return in 2061!
Since it's discovery, a lot has been learned about the mysterious comet, including some superstitions people had about it the first time they saw ominous streaks soaring across the sky. Needless to say, Halley's Comet has an interesting history tied to it!
Halley Is Named After An English Astronomer
Halley's comet is named after English astronomer Edmond Halley, a man who is responsible for recording some of the first transits of Mercury across the sun. He then went on to realize that the transit of Venus could be used to determine the size of the solar system.
In 1704, Halley was appointed Savilian professor of geometry at Oxford University. It was there that Halley reviewed reports of comets approaching Earth in 1531, 1607, and 1682. He eventually concluded that the comets were actually the same one returning over and over again, due to similar characteristics. Unfortunately, he did not live to see the return of Halley's comet.
The First Known Observation Took Place In 239 B.C.
According to the European Space Agency, the first known observation of Halley's Comet dates back to 239 B.C. and was by Chinese astronomers. They recorded the comet's passage around Earth in the Shih Chi and Wen Hsien Thung Khao chronicles.
The comet returned in 164 B.C. and 87 B.C., which makes historians believe that Halley is also mentioned in the Babylonian clay tablet records now housed at the British Museum in London. A Nature research paper noted, "These texts have [an] important bearing on the orbital motion of the comet in the ancient past."
Halley Is Darker Than Coal
It's quite amazing that we have been able to record sightings of Halley's Comet throughout history. All we see when it passes if a bright streak of light in the sky, after all! How did we even come to the conclusion that was light from a comet?!
Funnily enough, the comet itself is darker than coal, reflecting only 4% of the sunlight it receives. The brightness that we see with the human eye and through telescopes is just the sunlight reflected off of the dust and vapors in the tail of the comet.
The Comet's Tail Is Super Long
It's no surprise to hear that Halley's comet is quite the large space rock! The comet is 15 kilometers long and eight kilometers wide. The coma of Halley, or the "envelope" that circles around the comet, can stretch upwards to 100,000 kilometers when close to the sun!
This coma expands a great deal when it comes in close contact with the sun's radiation. As the comet warms, parts of it go from a solid to a gas state, giving the comet a fuzzy appearance when seen through a telescope. The solar wind blowing the coma backward creates the long tail.
It Was First Captured On Camera In 1910
Before 1910, there were only written records of Halley's Comet. It wasn't until that year when the comet flew by about 13.9 million miles from Earth, that it was captured on camera. The comet's picture was taken with a wide-angle camera at Lowell Observatory in Flagstaff, Arizona.
The photo shows a streak across the comet near the coma, of which is actually a meteor tail and not a scratch on the negative. Streaks on the top right are lights coming from the town of Flagstaff and the bright dot is the planet, Venus. A 1910 photograph sure did grab a lot of detail!
1910: The Year Of Doom
Aside from the photograph, the year 1910 was the year a lot of people thought the world was going to end. In a time when telescopes couldn't track the comet around its 76-year orbit, the search for its inevitable return that year was wildly reported in newspapers. Everyone was excited until astronomers realized that Earth was going to pass through the comet's 25-million-kilometer-long tail.
It got worse when the Yerkes Observatory announced the discovery of cyanogen, a deadly poison, in the comet's tail. The good news is that the world did not end on May 19, 1910, and the news quickly forgot about the comet.
Halley's Comet Is A Good Lesson In Prophecy
Edmond Halley astonished the 18th-century world by predicting the return of the comet's appearance every 76-years. He did so by using Issac Newton's law of gravity to learn about the characteristics of the comet in order to make the scientific prediction. In doing so, he proved that science could do what astrologers and prophets have been claiming to be able to do for years. Only they all failed.
The ability to predict future events is a scientific property called "classical physics." It relies on measurements and the clockwork of certain physical laws, such as gravity!
Author Mark Twain Has A Special Connection With The Comet
Writer, Mark Twain, famous for his various novels and short stories, was born on November 30, 1835. Two weeks later, Halley's Comet appeared. In his biography, he wrote that, since he was born with the comet's appearance he was going to die at its next appearance.
In 1909, Twain said, "I came in with Halley's Comet in 1835. It is coming again next year, and I expect to go out with it." He died on April 21, 1910, one day after the comet emerged from the far side of the sun.
The First Spacecrafts That Observed Halley Went Up In 1986
When Halley's comet came back to Earth in 1986, it was the first time in history we were able to send up spacecraft to get a closer look. Telescopes were only doing so much in terms of observations. Several spacecraft successfully made the journey, the fleet being dubbed the "Halley Armada."
Two joint Soviet and French probes, Vega 1 and Vega 2, were able to capture pictures of the comet's nucleus for the first time. Japan then sent their own probes, Sakigake and Suisei, both of which were able to gather scientific information to bring back to Earth.
We Can See Remnants Of The Comet Each Year
Even though Halley only comes around every 76 years, that doesn't mean we can't see remnants of the comet each year. The Orionid meteor shower that happens each October is composed of Halley fragments. This meteor shower comes from between the two constellations Orion and Gemini.
The shower lasts about one week, and in some years, the meteors occur at rates of 50-70 per hour. Pretty much, ask for a telescope during the holidays or your birthday and hope for some very clear skies come October!
There Is A Group Of Comets Called "Halley Family Comets"
"Family comets" tend to have similar characteristics as the main comet the family is named after. In Halley's case, the Halley family comets have orbital periods of between 20 and 200 years and orbital inclinations (slopes) extending from zero to more than 90 degrees. In other words, a long-period comet.
Astronomers believe that Halley family comets originate far out in the Solar System, in the Oort Cloud. This far reach of the solar system is said to be where long-period comets are born. If the gravity of other giant planets does not significantly influence the Halley-family comets, they will remain long-period comets.
Halley's Comet Is A Short-Term Comet
Halley's family comets are known as long-period comets because they take up to 200 years to orbit the sun. On the other side of the coin, Halley is known as a short-term comet because it only takes 76 years to orbit around the sun.
Short-term comets are now classified into two separate categories. Either Jupiter-family comets which have a period less than 20 years to orbit and do not extend much beyond Jupiter. And then there are Halley-type comets with orbit periods of 20-200 years and have highly inclined orbits.
Halley's Comet Is Mentioned Throughout Pop Culture
Halley's Comet has been made even more popular through its name being used in pop culture. Everything from games, to literature, to movies and television, and even song lyrics have alluded to or mentioned the comet in great length.
The most recent "appearance" of the comet was in the 2014 AMC television series Halt and Catch Fire. Although the show doesn't outright show the comet, it definitely alludes to it! One of the main characters, Gordon Clark, has a daughter named Haley who goes on to build a webpage called Comet. The site eventually evolves into one of the first search engines on the internet.
The Water On The Comet Is Different Than Earth's
A normal water molecule is made of two hydrogen atoms and one oxygen atom. Scientists have discovered that out of every 10,000 water molecules on Earth, three are not normal molecules, but instead heavy water molecules. This means that the two hydrogen atoms are replaced with deuterium.
To see if comet's had the same type of water as Earth, in 1986, the ESA probe Giotto flew by Halley's Comet to make observations. It was then discovered the Halley contained twice the amount of heavy water compared to normal water as Earth does.
Bayeux Tapestry Illustrates The Comet
Halley's Comet can be seen in the Bayeux Tapestry, an embroidery that illustrates the events of the Norman invasion of England and the Battle of Hastings in 1066. Since the comet seemed to appear out of nowhere, people of the time believed it to be a bad omen.
The comet is illustrated in the section of the tapestry showing one of King Harold's attendants telling him of the appearance of the "comet star." The attendant is saying that something bad is going to happen and that it was possibly a sign of God's wrath for the King un-rightfully claiming the English throne.
It Might be The Star Of Bethlehem
It has been thought that Halley's Comet is actually the Star of Bethlehem that the three Wise Men saw around the time that Jesus was born. Records suggest that the comet was seen in 12 B.C., but a record of another possible comet was made in 5 B.C.
The second "comet" appeared in the same place for seventy days without moving, as if hovering over something, quite possibly Bethlehem. Halley's Comet would have been bright enough to be described as a star, and comets have a tendency to linger in one spot. Who knows!
Halley's Lost Most Of Its Mass
Currently, Halley is thought to have a mass of about 2.2 hundred trillion kilograms and a density of roughly 0.6 grams per cm3. But recent studies have shown that due to the amount of material lost through sublimation each time the comet comes close to the sun, Halley has most likely lost about 80-90 percent of its original mass over its last 2,000-3,000 orbits.
At this rate, scientists hypothesize that the comet will lose enough mass over the next tens of millennia to either evaporate, split into two pieces, or be expelled from the solar system entirely.
Halley's Comet Brought Bad Luck
Halley's comet is "responsible" for war, famine, and bad fortune for a lot of people in history. In 980 A.D, Eilmer of Malmesbury saw the comet and right away thought of it as a bad omen. His village was attacked by the Danes soon after its appearance.
Malmesbury then saw it again in 1066, saying, "You've come, have you? … You’ve come; you source of tears to many mothers, you evil. I hate you! It is long since I saw you; but as I see you now, you are much more terrible, for I see you brandishing the downfall of my country. I hate you!"
Genghis Khan Thought Of Halley As His Personal Star
In 1222, Halley's Comet appeared once more. Unfortunately, that same year Genghis Khan was marching west. Khan thought of the comet as his own personal star, as it was moving westward as he was. Even though most people thought of the comet as a bad omen from the Gods, Khan embraced it.
It's said that he was so moved by the comet that it inspired him to dispatch his Mongolian troops and invade Europe. An invasion that left millions of people dead, so we guess the comet was a bad omen for some people that year.
The Comet Is A Snowy Dirtball
If you've ever been in the middle of an epic snowball fight and have no choice but to pick up snow that is covering a garden of soil, you know what a snowy dirtball is! Halley's makeup is that of a pile of rocks that are loosely bound together by gravity.
Like most comets, Halley is generally composed of a conglomeration of rock, dust, water ice, and frozen carbon dioxide, carbon monoxide, methane, and ammonia. The mixture of all of these elements gives the comet a dirty snowball-like appearance, as expressed by Dr. Fred Whipple.
