Halley’s Comet is by far the most famous comet of the Solar System. In this article on Halley’s Comet facts, we are going to learn about the comet in somewhat details.
We say ‘somewhat’ because we cannot make up information. All we can do is collate all the scattered information and put them in a single article.
But, before we begin with Halley’s Comet facts, we will like to ask you a question. Through antiquity, what did humans think of comets?
Don’t know? Okay, here is the answer:
Since times immemorial, humans used to think of comets as celestial wanderers or atmospheric anomalies or divine omens. Humankind had a notion that those celestial wanderers were one-time visitors of the Solar System and that they would flash and pass only to get lost somewhere in the dark oblivion of the limitless space.
This all changed because of a single man named Edmond Halley.
So, in this particular article on facts about Halley’s Comet, we are going to learn about its history, its origin, orbit, etc.
Shall we begin?
Halley’s Comet Facts: Some Tidbits | 1-5
1. The comet has the official designation of 1P/Halley. It also goes by the name Comet Halley.
2. Halley’s Comet is a short-period comet. A short-period comet is a type of comet which has an orbital period of less than 200 years.
3. Halley’s Comet in particular has an orbital period of 75-76 years. However, the period varied from 74 to 79 years since 240 BCE.
4. It is the only short-period comet that can be seen from Earth through naked eyes.
5. It is also the only short-period comet that a person might see twice in his lifetime.
Halley’s Comet Facts: A Journey Through History | 6-31
Halley’s Comet Facts: Ancient Times
6. This particular comet has been observed by astronomers and even definitively recorded since at least 240 BCE.
7. Chroniclers from medieval Europe, Babylonia and China have all made clear references of the comet.
8. Scientists believe that the comet has been speeding through the Solar System for as long as 200,000 years.
9. A paper was published in the year 2010 in the Journal of Cosmology by two researchers named Eric Hintz and Daniel W. Graham. According to the paper, the comet most likely appeared over the skies over Greece back in 466 BCE.
10. There are ancient accounts of the incident in which it is said that a meteorite as big as a wagon hit Hellespont but there was a huge fiery body in the sky that stayed visible for 75 days!
11. Graham and Hintz claim that looking back through timetable, the incidence nearly perfectly aligns with the projected appearance of Halley’s Comet back in the 5th century BCE.
12. While the Greek accounts might be true, there are definitive accounts of flybys of Halley’s Comet but they all came only a few centuries later. The most famous one was from Han Dynasty in China.
13. In Han Dynasty’s ‘Records of the Grand Historian’ has a description of a ‘broom star’ appearing in the sky. The record dates back to 240 BCE.
14. Then came the Babylonian clay tablets which records the flyby of the Halley’s Comet not once but twice – once in 164 BCE and then in 87 BCE.
15. Then came the records of the Romans who records the flyby of the Halley’s Comet in 12 BCE.
Halley’s Comet Facts: Inspiration for Horror and Fascination
16. Did you know that Halley’s Comet was often associated with bad omen in the antiquity? The comet was actually linked to many things bad spanning from natural disasters to deaths of kings.
17. The first century historian by the name Flavius Josephus went on to describe the comet’s appearance in 66 CE as ‘a star that resembled a sword.’ According to Josephus, it was sign of complete destruction of Jerusalem by the Romans.
18. In 451 CE, the comet, when it appeared, was looked upon as a sign of defeat of Attila the Hun in the famous Battle of Catalaunian Plains.
19. Several centuries later in 837 CE, the appearance of the comet was considered by the Roman Emperor Louis the Pious as a bad omen.
20. Louis the Pious took the appearance of the comet as a signal for his downfall and he eventually resorted to activities like giving alms to the poor, praying, fasting etc. to keep the bad omen at bay.
21. The Halley’s Comet appeared in 1066 CE. It was by far the most famous appearance of the comet as it coincided with what is known as Norman Conquest.
22. As the story goes, a few months before the scheduled sail of William the Conqueror to England, there was a sign seen in the heavens that man had never seen before.
23. Those who saw the sign considered that the ‘long-haired star’ was nothing but a very bad omen for England’s King Harold II.
24. It was considered as a prophecy which eventually went on to be true because in the Battle of Hastings. King Harold II was not only defeated by William the Conqueror but was also killed in the battle.
25. The famous Bayeux Tapestry has a section which depicts the crowd of fearful Englishmen and King Harold II watching Halley’s Comet passing through the sky.
26. The next several centuries that followed were no different. For instance, the comet appeared in 1222 CE. People say that the appearance of the comet inspired Genghis Khan to invade Europe.
27. In 1456, the Ottoman Empire invaded the Balkans. The event overlapped with the appearance of the Halley’s Comet.
28. Though people turned scientific eye towards Halley’s Comet during the 16th and the 17th centuries, there was still a lot of misconception and anxiety among people till as late as 20th century.
29. In 1910, the Halley’s Comet made a flyby prompting the New York Times to publish a news wherein it was claimed that Camille Flammarion – a French astronomer – had warned of a poisonous cyanogen gas tail will follow, destroying all lifeforms on earth by impregnating the planet’s atmosphere with the poisonous gas.
30. Though the claims were discarded by many from the scientific community, it did not fail to create panic. Several people ended up sealing up their homes to prevent gas fumes from entering.
31. Those people even went to the extent of stocking their homes with gas masks. Even more, many went to churches for praying and several others purchased anti-comet pills from street vendors.
Halley’s Comet Facts: The First Imaging | 32-37
32. In 1986 when the comet returned, it was put under telescope and scores of scientific studies took place for the first time in a proper way.
33. Because the appearance of the comet was greatly anticipated in 1986, scientists managed to capture the images of the comet using the 200-inch Hale Telescope located at Palomar Observatory in California.
34. The image was captured on 16th October, 1982. At the time of imaging, the comet was still at a distance of 1.65 billion kilometers or 1 billion miles or 11 AU from our Sun.
35. At the time of first imaging, the comet was well beyond the orbit of Saturn.
36. Halley’s Comet came closest to the Sun, that is, reached its perihelion on February 9, 1986. The closest distance of the comet from Sun was 55 million miles or 88 million kilometers or 0.587 AU.
37. Though the Halley’s Comet reached its perihelion on February 9, 1986, it was yet to get closest to Earth and it did so on April 10, 1986. At that time, the comet was at a distance of 39 million miles or 62 million kilometers or 0.417 AU from Earth.
Halley’s Comet Facts: Visits from Earthlings | 38-41
38. We earthlings are inquisitive and letting the comet just streak through the skies was not something we could sit and do. So, in March 1986, 5 interplanetary spacecrafts flew past the comet.
39. Of those 5 spacecrafts, two were from Japan and they were named as Suisei and Sakigake.
40. Two spacecrafts were from Soviet Union. They were Vega 1 and Vega 2. The fifth one was Giotto – a spacecraft from European Space Agency.
41. Giotto managed to get as close as 370 miles or 596 kilometers from the nucleus of the comet.
Halley’s Comet Facts: Size, Structure and Composition | 42-64
42. As far as the size of the comet is concerned, its dimensions are about 9.3 x 5 miles or 15 x 8 kilometers.
43. Did you know that the comet one of the least reflective and darkest objects present in our Solar System? It has an albedo 0.03. In simple words, it reflects only 3% of the sunlight that falls on it.
44. When the comet approaches the Sun, sublimating gas jets are expelled from the surface of the comet.
45. These jets of gases actually end up slightly knocking off the comet from its orbital path.
46. The process ends up producing a very bright tail and a faint tail. The bright tail is made of ionized gas and is known as ion tail. The faint tail is made of dust particles.
47. The ion tail also goes by the name coma. A coma is a small atmosphere. The ion tail extends up to 100,000 kilometers across.
48. As far as the composition of the ion tail is concerned, it is made of carbon dioxide, ammonia, methane and water.
49. If you compare the nucleus of the comet with the ion tail, the nucleus is literally very small. The overall mass of the nucleus of Halley’s Comet is estimated to be 242.5 billion tons or 2.2 x 1014 kilograms, which is considered to be relatively low.
50. The density, on an average, of the nucleus of the comet is estimated to be 0.6 g/cm3.
51. The very low density and the low mass of the comet the comet is actually made of a large number of small pieces that are held together pretty loosely.
52. The close-up observations by various spacecrafts, especially Giotto suggests that the nucleus of the comet is a mixture of various volatile ices, water ice, organic (carbon-rich) dust and rocky (silicate) material.
53. An insulating crust covers nearly 70% of the nucleus. The crust prevented sublimating of the water ice beneath the surface crust.
54. The remaining 30% of the nucleus is active and it is this part that is responsible for producing the ion tail and the dust tail.
55. The insulating crust is extremely dark. It is blacker than the coal that we find on Earth. It is this crust that makes Halley’s Comet one of the darkest objects in our Solar System.
56. Vega 1, the Soviet spacecraft that that visited the Halley’s Comet when the comet was at a distance of 73 million miles or 118 million kilometers of 0.79 AU from the Sun, found that the surface temperature of the comet was 188°F or 87°C or 360 Kelvins.
57. How did a comet at such a distance have such high surface temperature? That is made possible by the extremely dark crust which absorbs most of the sunlight.
58. The spacecrafts observed that as the comet continued to rotate on its axis, the rate at which gas and dust was emitted out varied significantly. This variation happened as different active areas of the surface came in contact with sunlight.
59. The observations made by the spacecrafts revealed that the gases that were ejected by the comet nucleus had a composition of 80% water vapor, 17% carbon monoxide, about 3-4% carbon dioxide and very trace amounts of hydrocarbons.
Note that recent sources state that carbon monoxide content is 10% and there are traces of ammonia and methane as well in the gases.
60. The dust particles that are ejected by the comet nucleus are CHON compounds. What is CHON? It stands for Carbon–Hydrogen–Oxygen–Nitrogen. These CHON compounds are pretty common in outer Solar System.
61. Apart from CHON compounds, there are silicates (like the ones we find in the terrestrial rocks) in the dust particles as well.
62. The images captured by Giotto and Vega missions of ESA and the Soviets revealed that the surface of Halley’s Comet has varied topography. There are hills, depressions, ridges and mountains and at least one crater.
63. Did you know that there was a time when it was thought that Halley’s Comet was responsible for delivering water to our Earth?
64. Such conclusion was arrived after studying the studying the ratio of deuterium to hydrogen present in the water of Halley’s Comet. The ratio turned out to be chemically similar to that of water found on Earth. However, subsequent observations eventually proved that the comet delivering water to Earth in the distant past was very unlikely.
Halley’s Comet Facts: Lifespan and Disappearance | 65-71
65. 10-million-years – POSSIBLY! That is the possible lifespan of Halley’s Comet as predicted by Vitaly Vecheslavov and Boris Chirikov – two Russian astronomers.
66. This time span was predicted by the two astronomers in 1989 after they studied and analyzed 46 apparitions of the comet that they took from historical records and even computer simulations.
67. The study that they conducted showed that the dynamics of Halley’s Comet was unpredictable and chaotic over longer timescales.
68. In 2002 a different study conducted by David C. Jewitt showed that Halley’s Comet will most likely split into two pieces or simply evaporate by next few tens of thousands of years.
69. Jewitt also came up with an alternate possibility of the ultimate fate of the comet. He proposed that instead of evaporating or splitting into two pieces, the comet may be completely ejected from the Solar System in next few tens of thousands of years.
70. A different study that was conducted by D.W. Hughes et al. had a different proposition. According to the study, the mass of the comet has decreased by a whopping 80%-90% over the last 150,000 to 230,000 years or approximately 2000-3000 revolutions.
71. By that estimate, D.W. Hughes et al. propose that within next 300 revolutions, which is about 25,000 years from now, the comet will completely evaporate.
Conclusion: Halley’s Comet is an interesting celestial object that sparked imagination, love and fear. Even today, there are people who believe that the next time it appears on our skies, it will lead to complete end of life as we know on Earth. Then, there are others who just want to live long enough to see the spectacle that the universe has to throw at us.
Having said that, we will like to mention that this article on Halley’s Comet facts is far from being complete. There are a lot more that can be put here. If you are wondering what those facts are, you can check out our e-book on Halley’s Comet. It will be a fantastic read we promise and will be priced at only $1.50.