Comet research

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Comet leaflet from 1687, the comet as a harbinger of death and destruction

Comet research is the study of comets .

history

Comets have always fascinated people. Unlike the stars and planets , they kept appearing out of nowhere and with no recognizable regularities. They were therefore regarded as signs of the gods . In the first attempts at scientific observation, comets were viewed as atmospheric phenomena. Aristotle described in his book meteorologika how flammable gases escape from crevices and ignite in the world under the moon (sublunar). A quick release of these gases would create shooting stars , a slow release would create comets .

Messengers of fate

Halley's Comet on the Bayeux Tapestry (top right)

In the course of time the causality was reversed, in that the comets themselves were supposed to influence events on earth. The completely inexplicable comet appearances were seen as announcing or causing natural or other catastrophes , examples of which could always be found. So the comet of 79 AD was seen as the announcement of the eruption of Vesuvius with the subsequent fall of Pompeii , and during the defeat of the Anglo-Saxons against the Normans in the Battle of Hastings (1066), which was immortalized on the Bayeux tapestry , the then visible Halleysche became Comet interpreted as a bad omen. See special article: Comet Fear

In the Christian Middle Ages they were seen as signs sent from above, behind which the will of God stood: "There will be tremendous earthquakes and famine in many places, and tremendous signs will be seen in heaven" ( Luke 21:11). The outbreak of the plague in 1635, in which more than 90,000 people died in London alone , was seen as God's punishment because it was preceded by a comet that same year. In 1835, Halley's comet, which was visible again, was assigned a series of catastrophes, including a major fire in New York , the outbreak of several wars in Central and South America and a massacre in Africa .

When Earth crossed the tail of Halley's Comet in 1910 , it sparked greatly exaggerated concern and sales of nearly a million gas masks . The reason for this was that traces of hydrogen cyanide had previously been detected in the tail . Since comet tails have a very low density, however, its contents could only penetrate the atmosphere in a highly diluted form.

Scientific beginnings

Only Tycho Brahe was able to show through detailed studies of the comets of 1577 and 1585 that comets move beyond the lunar orbit. After Isaac Newton demonstrated with his new theory of gravity that comets usually move on elongated ellipses, Edmond Halley refined the methodology and determined the comet's orbit period from 1682 to be around 76 years, consistent with the cometary appearances of 1531 and 1607. He was thus able to predict the return of a comet for the first time in 1758; however, he could no longer experience it.

The next comet with a periodic orbit was found by Johann Franz Encke ; for its orbit it found in 1821 the period of 3.3 years. The orbit of Encke's comet was subsequently measured regularly, and deviations from Newton's law of gravitation were found for the first time.

Modern comet research

Many historians see the beginning of modern comet research in the spectroscopic examination of the comets of 1864 and 1866. In 1866 Giovanni Schiaparelli was also able to show that the strong Perseid activity of 1863 was related to the comet Swift-Tuttle .

There has long been speculation about the nature of comets, but it was not until Friedrich Wilhelm Bessel who was on the right track in the early 19th century when he attributed the brightness of comets to the vapors of a solid body. This evaporation also offered an explanation for the orbital deviations of Encke's comet, but it was not until 1951 that Fred Lawrence Whipple took up the idea again, his theory of the dirty snowball is still valid today with reservations.

In 1950, Jan Hendrik Oort examined the orbits of long-period comets and found an accumulation of apheld distances between 50,000 and 150,000  AU , with orbital inclinations and directions of rotation being statistically distributed. He therefore postulated a large cometary reservoir at this distance, the Oort cloud , which consists of around 1 billion objects . Since this cloud neither the number nor can explain the web properties of short-period comets, postulated Gerard Kuiper another comet reservoir between 35 and 50 AE, existing from about 100 million to 10 billion objects Kuiper Belt .

After comet research received very little attention for much of the 20th century, it experienced a significant boom in the 1980s due to the possibilities of space travel .

Comet missions

In the 1980s, space missions were undertaken for the first time , which mainly served to study comets. In 1985 the International Cometary Explorer flew through the tail of Comet Giacobini-Zinner , and in 1986 Halley's Comet was the target of five probes :

  • The Japanese Sakigake and Suisei probes approached the core to within 7 million and 150,000 kilometers, respectively
  • The Soviet probes Vega 1 and Vega 2 approached 8,000 to 9,000 kilometers and thus crossed the coma
  • The European probe Giotto flew 600 kilometers past the nucleus and provided images of a cometary nucleus for the first time

More missions on comets:

Amateur astronomy

Since the 1980s, the focus of comet research has been on probe missions because, on the one hand, the cometary nucleus cannot be examined more closely with telescopes and, on the other hand, on-site measurements are very important for further understanding the comets and the formation of our solar system. Nevertheless, the work of amateur astronomers is also important in comet research ; Sometimes they even get specific tasks from professional astronomers, for which the help of volunteers is essential.

Near Earth Objects (NEO)

The search for comets is very time-consuming, as a lot of telescope time is required to regularly search the entire celestial sphere for new comets - professional astronomers do not receive any budget funds for this telescope time . That is why even today, in the age of highly sensitive large and space telescopes, many new comets are still being discovered by amateurs, if so. This fact is very worrying, since comets belong to the near-earth objects , that is: their orbit crosses the orbit of the earth, and there is therefore a risk of collision. The impact of a comet on Earth would, depending on its size, lead to a regional, possibly even a global catastrophe - the Tunguska event e.g. B. is attributed to a small comet fragment that is completely vaporized in the atmosphere.

Halley's Comet

During the 1986 Halley Comet missions , the amateurs were asked to form an earth-spanning ring to observe the comet. Coordination centers have been set up in some countries to collect the data. These position determinations were required to calculate the orbit corrections of the Giotto probe, since the sublimation processes of the comets in the vicinity of the sun lead to permanent, unpredictable orbital deviations - without the help of the amateurs, Giotto's great success would not have been possible.

Web links

Wikisource: Comets  - Sources and Full Texts