Chapter 27 Chapter 3 Comet

In a lecture on comets, Professor Palmier Rosset gave the following definition of comets based on the outstanding insights of various astronomers: "A comet is a kind of celestial body, which is composed of a nucleus in the center, a tube in the form of a cloud, and a bright tail in the shape of a broom. Due to the large eccentricity of its orbit around the sun, people on the earth can only See it within a certain period." Palmieri Rosset believes that his definition is very precise.However, this kind of celestial body sometimes has no nucleus, or no coma and tail, but it is still a comet.

He said that according to Arago's theory, for a celestial body to become a comet, the following conditions must be met: 1) It has its own running track; 2) Its orbit is oblong and elliptical, so it can go to places that are extremely far away from the sun and the earth. A celestial body will be distinguished from a star if it has the first condition, and it will be distinguished from a planet if it has the second condition.Therefore, if a celestial body is neither a meteor nor a planet or a star, it can only be a comet. Every time Professor Palmier Rosset explained the knowledge about comets to people, he never doubted that he would be taken to the solar system by some comet one day.He has always had a special fondness for such celestial bodies—whether they have a coma or not.Perhaps he had already foreseen that this day would happen!His knowledge of comets is extensive.When the comet collided with the earth, what he regretted most in Vermentera must be that no one came to listen to his speech, otherwise he would have given a lecture at once, and explained the problem in more detail in the following points:

1) How many comets are there in space? 2) Which comets are periodic, i.e. recurring within a certain period of time?Which comets are aperiodic comets? 3) Under what circumstances will the earth collide with a comet? 4) What are the consequences of the collision?Is it related to the quality of comet nucleus? The audience will be greatly satisfied if they can hear for themselves what Professor Palmier Rosette has to say on the above-mentioned questions. We will now replace him in this chapter to discuss these four issues. First the first question: how many comets are there in space?

Kepler once thought that there were as many comets in the sky as there were fish in the water. According to the number of comets orbiting between the sun and Mercury, Arago came to such a conclusion: there are 17 million comets in the solar system alone. According to Rambert, there are 500 million comets within the distance of 1.456 million kilometers from the sun to Saturn. Some people think that there are 740 trillion comets in this interval. The reality is that no one knows how many there are, because no one has counted them.And I don't know how to count them, but the number must be very large.In order to illustrate this problem, we might as well borrow a metaphor made by Kepler: if a fisherman stands on the surface of the sun and fishes into space.A comet can be "caught" with a fishing rod.

That's nothing.In the vast space beyond the solar system, there are countless comets.They roam freely in space without certain rules, leaving one gravitational range and entering another gravitational range at every turn.They move in and out of the solar system.Some comets have never been seen on the earth, but they will suddenly appear in the sky of the earth, and then disappear forever, never to be seen again. Comets active in the solar system, do they have fixed orbits, will they not collide with each other, and will not collide with the earth?No.Their orbits are always changing under the influence of external forces.Such orbits can vary from elliptical to parabolic or hyperbolic.For example, Jupiter is an "expert" who interferes with the orbit of comets.Astronomers have found that it always stands in the way of comets, exerting a powerful influence on these small objects.This is mainly due to its strong gravitational pull.

The above is the basic situation of the comet "family", whose members are simply countless. Now talk about the second question: Which comets are periodic comets?Which comets are aperiodic comets? If you look at the history of celestial bodies, you will find that there are 500 to 600 comets that have been carefully observed in history.But only forty of them have known their revolution period accurately. These forty comets are divided into periodic comets and non-periodic comets.Periodic comets reappear in the Earth's sky at essentially regular intervals.Aperiodic comets are extremely far away from the sun, and it is unknown when they will return.

Among the periodic comets, sixteen are so-called "short-period comets" whose orbits have been accurately calculated.This is Halley's Comet, Encke's Comet, Gambard's Comet, Faye's Comet, Brosen's Comet, Aleister's Comet, Tuttle's Comet, Venaker's Comet, Vico's Comet and Domper's Comet. Regarding the situation of these sixteen comets, it is necessary to explain a few words here.For one of them, like Gallia, had encountered the earth. Halley's Comet was first discovered.It is said to have been seen as early as 134 and 52 BC, and thereafter in 400, 855, 930, 1000, 1230, 1305, 1380, 1456, 1531, 1607, 1682, 1759 and 1835 appear several times.It moves from east to west, the opposite direction of the planets orbiting the sun.The interval between its recurrence is 75 to 76 years, but due to the influence of Jupiter and Saturn, sometimes it will be delayed by 600 days. When the comet appeared in 1835, the outstanding astronomer Herschel deliberately rushed to the Cape of Good Hope to choose a better observation place, and observed it until the end of March 1836.The perihelion of Halley's Comet is 88 million kilometers, which is smaller than the perihelion of Venus, which is a bit like Galia.Its aphelion is 5.2 billion kilometers, beyond the orbit of Neptune.

Comet Encke has the shortest revolution period, with an average of only 1,205 days, or less than three and a half years.It moves prograde from west to east and was discovered on November 26, 1818.After calculation, it was found that it was a comet that appeared in 1805.Astronomers thus predicted the law of its appearance, and then it reappeared in 1822, 1825, 1829, 1832, 1835, 1838, 1842, 1845, 1848, 1852....It is punctual and always appears on the horizon at a certain time.Its orbit is inside the orbit of Jupiter, its aphelion is no more than 624 million kilometers, and its perihelion is 52 million kilometers, which is closer to the sun than Mercury.Another important situation is that the maximum diameter of its elliptical orbit is gradually shrinking, and the average distance from the sun is also getting smaller and smaller.So comet Encke will one day fall to the sun and turn into ashes, and even before it falls to the sun, it will be completely vaporized.

Comet Gambard, also known as Comet Billa, was seen many times in 1772, 1789, 1795, and 1805, but its orbit was not determined until February 26, 1826.It moves in a prograde direction and takes seven years to circle the sun once.Its perihelion is 130,804,000 kilometers, which is slightly closer than the earth to the sun.Its aphelion is 941.48 million kilometers, beyond the orbit of Jupiter. A strange thing happened in 1846: Comet Biela suddenly split into two and appeared in the sky.This is obviously caused by the explosion of its inner strength.The two fragments have traveled together since then, only 240,000 kilometers apart.By 1852, however, this distance had increased to two million kilometers.

Comet Faye, first discovered on November 22, 1843, also moves in a prograde direction.After calculating its orbit, it is predicted that it will reappear in 1850 and 1851, that is, seven and a half years later.This prophecy later came true.Its perihelion is 258.6 million kilometers, which is farther than the orbit of Mars; its aphelion is 906.24 million kilometers, which greatly exceeds the orbit of Jupiter. Comet Brosen moved in a prograde direction and was discovered on February 26, 1846.Its revolution period is five and a half years.The perihelion is 98,456,000 kilometers, and the aphelion is 864,000,000 kilometers.

Among other short-period comets, Comet Aleister orbits in just over six and a half years. In 1862, it was only 44 million kilometers away from Jupiter.Comet Tutt's orbital period is thirteen and two-thirds years.Comet Vinaker is five and a half years, and Comet Don Pere is close to five and a half years.As for Comet Vico, it seems to have lost its way in space, going nowhere.But none of these comets has been as comprehensively observed as the first five. Now let's take a look at some of the major "long-period" comets.Of these comets, forty have been precisely studied. Comet 1556, also known as Comet Charlie-Gold, was expected to reappear in 1860, but it didn't. The 1680 comet studied by Newton, Whiston believes that if it approaches the earth, it is likely to cause a meteor shower.The comet may have been discovered in 619 BC and 43 BC, and again in 531 and 1106 AD.Its cycle is about six hundred and seventy-five years.When it is at perihelion, it is so near to the sun that it receives from the sun twenty-eight thousand times as much heat as the earth, or two thousand times the melting point of iron. Comet 1586 was as bright as a first-magnitude star. The comet of 1744 trailed several tails like a pasha circling the Ottoman emperor. Comet 1811 had a halo with a diameter of 684 kilometers.Its coma is 1.8 million kilometers long and its tail is 180 million kilometers long. Some people believe that the comet of 1843 is the same comet discovered in 1668, 1494 and 1317, which was observed by Cassini.There are different opinions about its revolution period.It keeps a distance of 48,000 kilometers from the sun and runs at a speed of 60,000 kilometers per second.It receives from the sun as much heat as 47,000 suns send to the earth.Its tail is also clearly visible during the day, as high temperatures greatly increase the intensity of light. Comet Donati once brightened the northern night sky, but its volume is only 1700th that of the Earth. Comet 1862's bright halo was exactly like a shell. Finally, the period of the comet of 1864 was by no means less than 280,000 years, and it seemed that it was about to disappear forever in the vastness of space. The third question, under what circumstances will the earth collide with a comet? If you draw the orbits of the planets and the orbits of the comets on a piece of paper, you'll see that the orbits usually intersect each other, but that's not the case in space.The orbital planes of these planets all maintain a certain angle with the ecliptic, that is, the orbital plane of the earth.In order to prevent other planets from colliding with the earth, the Creator has "arranged" in advance.But why didn't any of these plethora of comets hit the earth? This is because: the earth will never leave the ecliptic plane, and its orbit is completely contained in the ecliptic plane. For a comet to collide with the Earth, the following conditions must be met: 1) Enter the ecliptic plane to meet the earth; 2) The place where the comet enters the ecliptic plane within a certain period of time is exactly a point on the earth's orbit; 3) The distance between the center points of two planets should be smaller than their radius. Can these three conditions be met at the same time to cause a collision? Someone raised this question to Arago.He replied: "We can answer this question based on calculations that show that when a never-before-seen comet appears near the Earth, the chances of it colliding with the Earth are one in 281,000,000. " Laplace did not rule out the possibility of such a collision, and described the possible consequences of such a collision in his book "A Survey of the Universe". Does this claim about collision hold water?Everyone just speaks according to his own temperament.It should also be seen that the two points on which this eminent astronomer rests are infinitely variable.Because he required: 1) the perihelion of the comet should be smaller than that of the earth; 2) the diameter of the comet should be equal to a quarter of the diameter of the earth. What is being discussed here is only the collision of the nucleus of the comet with the earth.If the coma is included, the probability of a collision increases tenfold, to one in 28.1 million. Arago, speaking of the first question, also said: "If a comet collided with the earth, it would destroy the whole human race. This unexpected visitor would be as dangerous to everyone as there is only one white ball in a jar containing 281 million balls. Only the first Being able to draw this white ball out once means that human beings will be destroyed." We can see from these statements that the collision between the earth and a comet is not absolutely impossible. So has this happened before? Astronomers say no.Arago believes: "The earth's rotation axis has never changed, so we can safely conclude that the earth has not collided with a comet. Because if this happened, the earth's rotation axis would be replaced by a temporary axis, The range of activities of the earth will constantly change, but we have not found this change so far. Therefore, this invariance of the range of activities of the earth proves that the earth has never collided with comets in history... At the same time, we cannot According to some astronomers, the formation of the Caspian Sea, which is more than 100 meters below sea level, is attributed to the collision of comets." There seems to be no doubt that there have been no collisions in the past.But has this possibility ever arisen? Here I want to talk about a false alarm caused by Comet Gambard. In 1832, the appearance of Comet Gambard caused panic all over the world.By some odd coincidence, Comet Gambard's orbit nearly crosses Earth's.It is calculated that the comet will pass very close to Earth's orbit before midnight on October 29.Will Earth get there by then?If it gets there, Earth will meet the comet.According to Obert's observations, the radius of Comet Gambal is five times that of the Earth, so part of the Earth's orbit will be submerged by the comet's cloud-like material. Thankfully Earth didn't get there until a month later, on November 30.Since the earth's revolution speed is 2,696,000 kilometers per day, when she got there, the comet was already 80 million kilometers away from the earth. great!But if the Earth got there a month earlier or the comet a month later, a collision would be inevitable.Is it possible for this phenomenon of arriving early or arriving late?Obviously possible.Although there will be no disorder in the movement of the earth, no one dares to say that the speed of the comet will not slow down. It is affected by various aspects on the way. Therefore, although the collision between the earth and comets did not happen in the past, the possibility of collision undoubtedly existed. In fact, when Comet Gambard passed by the earth in 1805, the distance was much closer than this time, only 8 million kilometers.Just because everyone didn't know, it didn't cause any panic. The comet of 1843 was quite a different story, when it was feared that the Earth would be swept at least briefly by its tail, which would seriously pollute the atmosphere. The fourth question: Since the earth and the comet may collide, what will be the consequences of the collision? This depends on whether the colliding comet has a nucleus. These space-roaming comets are like fruits, some with nuclei and others with nuclei. Comets without nuclei are composed of very thin clouds and mist, through which even tenth-magnitude stars can be seen clearly.Therefore, its morphology often changes and is difficult to identify.The tail of the comet is also this wonderful material, which seems to be vaporized at high temperature when the comet is close to the sun.For example, some comet tails only begin to appear gradually when they are 120 million kilometers away from the sun, which is less than the distance between the earth and the sun. Some are like a tuft of long feathers, and some are like an opened folding fan.But there are also comets with relatively dense material composition, which can resist high temperature, so there is no comet tail. Therefore, if a comet without a comet nucleus meets the earth, there will be no collision worthy of the name.The astronomer Faye said that the cloud-like material of a comet is worse than the ability of a spider's web to stop a bullet.The substances that make up the tail and coma of a comet are nothing to be ashamed of if they do not impede the health of the human body.But the concern is that the substance could be a hot gas that incinerates the Earth's surface, or that harmful gases could enter the Earth's atmosphere and interfere with normal life.But the latter possibility is very small.Barbinay believed that the atmosphere on the earth, even in the upper part of the sky, is much denser than the coma and comet tail, and it is difficult for harmful gases to invade.Newton also said that if a non-nuclear comet with a radius of 1.46 billion kilometers is compressed to a density equivalent to that of the earth's atmosphere, a small wine glass with a diameter of 25 mm can hold it. therefore.If a comet were composed only of nebulous matter, it would pose little danger if it were to meet the earth.But what would a collision look like if the comets were made of hard matter? First, is there such a comet?The answer should be yes.When a comet reaches a certain contraction force, its gas becomes solid.At this time, when people look at a star from a distance on the earth, if the comet passes through the middle, it will cover that star. Anazagor said that during the time of Celses in 480 BC, the sun was once obscured by a comet.Likewise, Dijon had seen this phenomenon a few days before August's death.At that time, it could not be the moon that covered the sun, because the moon was on the other side of the earth. Some astronomers who study comets have taken issue with the two oppositions, and they may be right.But after the last two discoveries, there is no doubt about the existence of nucleated comets. Both the comet of 1774 and the comet of 1828 had blocked the 8th magnitude star.At the same time, through direct observation, it is also believed that the comets of 1402, 1532 and 1744 all had hard comet nuclei.As for the comet of 1843, there is no doubt about it.The comet was on the sky near the sun at that time, and even at noon, it could be seen clearly without a telescope. It can be seen that some comets do have hard comet nuclei.Some people have also measured the volume of this comet.For example, the actual diameters of the 1798 comet and the 1805 comet (i.e., Gambard's comet) were 44 to 48 kilometers, while the actual diameter of the 1845 comet was 12,800 kilometers.It can be seen that the core of the comet in 1845 was larger than that of the earth, and if it collided with the earth, it may suffer less damage. As for the major cloud comets that have been observed, their diameters are all between 28,800 kilometers and 1.8 million kilometers. Thus, according to Arago, there is or could be in space: 1) non-nuclear comets; 2) Comets whose cores may be cloudy; 3) Comets with hard, dense cores that are brighter than planets. Before discussing the consequences of a collision between the Earth and a comet, we should point out that, if not a direct collision, the consequences would have been severe. Because, if the comet is very large, it is very dangerous even if it passes by the earth.Of course, if the size is small, there is nothing to be afraid of.For example, although the comet was only 2.4 million kilometers away from the earth in 1770, its revolution period to the earth did not change even for a second, but the earth delayed its period by two days. But if the comet is the same size as the earth and only 220,000 kilometers away from the earth, it will extend the earth's sidereal year by 16 hours and 5 minutes, and will tilt the ecliptic by two degrees, and may even bring the moon into the sky. Walk. Therefore, the collision result is very clear, and three situations may occur: Either a comet brushes lightly across the surface of the earth, leaving a portion of its material behind; or, it carries a few small patches of land on the earth--this is the case with Gallia; or, a comet falls on the earth and becomes a new land. But in either case, the Earth's orbital speed would suddenly disappear.At this time, people, trees and houses on the earth will be thrown into the air at the original speed of 32 kilometers per second.The waters will come out of the sea and cover everything.The lava in the center of the earth will break out due to the vibration and overflow on the surface.The Earth's axis of rotation will change, and a new equator will appear.In addition, once the earth's revolution speed disappears, the sun's gravitational force on the earth can no longer offset the earth's centrifugal force, so the earth will be directly attracted by the sun, and after sixty-four and a half days, it will fall to the surface of the sun and turn into ashes . According to Tandar's theory, heat energy is nothing more than a form of motion.After the earth's speed suddenly disappears, it is naturally converted into heat energy.In this way, everything on the earth will be vaporized in a few seconds under the high temperature of millions of degrees. But having said that, the probability of the Earth colliding with a comet is only one in 281 million. Gallia's collision with the earth this time was, as Palmillian Rosette later said, "undoubtedly due to the drawing of the white ball".