Every year in early May, the inhabitants of the Earth observe the meteor stream Eta Aquariids. Its origin is interesting. The source of the Eta Aquariids is the tail of the same comet, Halley’s Comet, whose name is a noun and is well known even to people not interested in astronomy.
From this material, you will learn about where Halley’s Comet came from, what it owes its fame to, and when it will return next time.
The most important comet in the history of science
Let’s start by answering the main question: What does Halley’s Comet owe its fame to? Why is its name so widely known compared to other comets?
Source: E. Kolmhofer, H. Raab; Johannes-Kepler-Observatory, Linz
Throughout history, the inhabitants of the Earth have regularly observed the appearance of tailed stars in the sky. They were often associated with harbingers of coming misfortunes – wars, plagues, natural disasters. As for scientific ideas about the nature of comets, up to the Renaissance dominated the view of Aristotle, who believed that comets are disturbances in the Earth’s atmosphere. This position was disproved by Tycho Brahe, who in 1577 measured the parallax of one of the comets and proved that it was at least four times farther away than the Moon.
As scientific knowledge accumulated, scientists gradually began to realize that comets are celestial bodies that approach the Sun. However, it remained unclear whether they orbit around the Sun in regular orbits or simply pass through the Solar System and then disappear forever.
Astronomer Edmond Halley had the answer to this question. In the early 18th century, he calculated the orbits of several dozen known comets and noticed the similarity of several of them. The intervals between their appearance were 75-76 years. Halley made the bold assumption that it was the same object. In 1716, he published detailed calculations, predicting that the comet would next return in 1758.
Halley himself did not live to see that date. But on December 25, 1758, astronomer Johann Palitzsch did discover the comet he had predicted. This event was the first triumphant confirmation of Newton’s law of universal gravitation. The comet was named in Halley’s honor and is now rightly considered the most important comet in the history of science.
Historical visits of Halley’s Comet
After it became clear that Halley’s Comet is a regular visitor to the Earth’s sky, scientists have tried to find evidence of its past appearances – and have been quite successful in doing so. According to some estimates, about one-eighth of all references to comets in various written sources are in one way or another associated with Halley’s Comet.
Such “popularity” is explained by its unique characteristics. Although many brighter long-period comets (i.e., those with an orbital period of more than 200 years) appear every century, Halley’s Comet is the only short-period comet visible to the naked eye that appears in the Earth’s sky at small (by historical standards) intervals.
The first reliable mention of Halley’s Comet in historical records dates back to 240 B.C. Chinese chroniclers noted the appearance of the comet, which appeared in the east and moved northward. During subsequent visits, it was also observed by the Babylonians, Greeks, and Romans.
Source: British Museum
Given the regularity of the comet’s appearances, it is not surprising that many of them coincided with important events in Earth’s history. Thus, some historians correlate its visit, which occurred in 12 BC (i.e., just a few years before the generally accepted date of birth of Jesus Christ), with the Star of Bethlehem. Although, of course, this interpretation is quite controversial.
The comet’s appearance in 451 coincided with the invasion of Attila and the Battle of the Catalaunian Plains. Another famous visit of the comet occurred in 1066 A.D. Contemporaries considered it a bad omen and later linked it to the Battle of Hastings, during which the Normans conquered England.
And the comet’s visit in 1910 even provoked panic. The fact that the spectral analysis of its tail revealed the presence of poisonous gases, cyanide, and carbon monoxide. Since on May 18, 1910, the Earth was to pass through the tail of the comet, the discovery provoked numerous predictions of the end of the world, which was promptly used by various charlatans who began to sell “anti-comet” respirators and pills.
Interestingly, the famous American humorist writer Mark Twain wrote the following in his autobiography in 1909: “I came into the world in 1835 together with Halley’s Comet. She will reappear next year, and I think we will disappear together”. He was right.
The last time Halley’s Comet visited the inner Solar System was in 1986. Ironically, this visit was one of the most “unspectacular” in history. The comet and the Earth were on opposite sides of the Sun, and light pollution in the sky also played a role. Nevertheless, a whole armada of five spacecraft was sent to the tailed guest: the Soviet Vega-1 and Vega-2, the Japanese Sakigake and Suisei, and the European Giotto.
The closest to the comet managed to get to the probe Giotto. It flew at a distance of 596 km from its nucleus. It turned out that the nucleus of Halley’s comet has a peanut shape and reflects only 4% of the sunlight falling on it, which is comparable to the albedo of charcoal. Its dimensions are 15 x 7.2 x 7.2 km. The nucleus of the comet has a very varied topography, including elevations, ridges, depressions, and traces of impact craters.
The origin of Halley’s Comet
So, where did Halley’s Comet come from? Most likely, it was once part of the Oort cloud, a giant repository of icy objects left over from the formation of the solar system. At some point, its orbit was disturbed during gravitational interactions with some other bodies, after which it moved into the interior of the Solar System.
Astronomers estimate that Halley’s Comet has been in its current orbit for several tens to several hundred thousand years. It is impossible to make a long-term calculation because its trajectory and orbital period change slightly after each approach to the Sun.
In any case, it is clear that during its time in its current orbit, Halley’s Comet has lost a significant portion of its original mass. By some calculations, its nucleus has lost 85% to 90% of its substance. This means that during its first visits, which took place back in Paleolithic times, it shone much brighter in the sky than it does now.
The next visit of Halley’s comet
The previous time Halley’s Comet passed the perihelion of its orbit was in 1986. Since then, it has been gradually moving away from the Sun until December 2023, when it passed the aphelion of its orbit. It is located at a distance of 5.3 billion kilometers, which is comparable to the distance to Pluto.
After that, the comet began its return. But it won’t happen for a while. Its next perihelion comet will pass on July 28, 2061. This time its location in the sky will be much more favorable for observations than in 1986. According to calculations, its apparent stellar magnitude will be -0.3. This is comparable to the brilliance of the star Arcturus.
The comet’s visit in 2134 will be even more spectacular. On May 7, the comet will pass at a distance of 13.6 million kilometers from Earth. At this point, its apparent stellar magnitude will be -2.0 and it will be brighter than Sirius.
If we talk about more distant prospects, with each new perihelion, Halley’s comet will continue to lose its substance and decrease in size. Most likely, after a few thousand revolutions, it will either completely vaporize or break up into several parts. But a scenario in which it is ejected from the Solar System into interstellar space is also possible. In this case, there is a very small probability that in millions of years, Halley’s Comet will approach some other star system and decorate its sky, as it once decorated the sky of our planet.
