Last days for the visit of Hale-Bop, one of the largest of the comet stars, in the sky of the country. The last one was here about 4,000 years ago and is supposed to drop by for another visit in about 2,000 years
Every evening, right after sunset, a strange star recently appears in the western sky. Even with the naked eye it is possible to notice that he is different and special - an aura floats around him, and a tail hangs next to him. This is Comet Hale-Bop, named after the two American amateur astronomers who discovered it about two years ago. Looking through binoculars, even if it is not particularly strong, reveals the comet in all its splendor, and is recommended for anyone who likes the secrets of the sky. The comet arouses curiosity and wonder in all who observe it: why did it suddenly appear, what is its tail, where did it come from and where is it headed.
Most of us accept the comet with a certain equanimity. Only a few are sufficiently versed in the taps of the heavens to be surprised by the appearance of a "new" star among the thousands of other stars; And most of us cannot recognize by name and in its place even a single star in the sky. This was not the case in ancient times. Back then, man was much closer to the phenomena of the sky - beginning with the names of the prominent stars of the Sabbath and the seasonal appearance of constellations ("constellations") and ending with the tortuous orbits of planets such as Mars and Jupiter. In those days, the appearance of a comet was considered a sensational news event. This can be likened to the astonishment that a veteran Tel Avivian would have if he woke up one morning and saw through his window an eighty-story skyscraper that had been erected overnight in the middle of Rabin Square.
The ancient astrologers were not content with reading books about the orbits of the stars and the zodiac signs. They were also astronomers for everything, watching the sky night after night and knowing each star by name and its orbit. Their belief in the influence of the stars on human life, which has strangely survived to this day, is explained by the fact that the sky provided them with a kind of complicated clock, the course of which can be predicted in advance. It was convenient to believe that with its help one could also predict the fate of human beings. The appearance of a prominent comet, which occurs unexpectedly once every decade or two, was then a source of astonishment and concern. The comet symbolized the breaking of the sacred heavenly order, and it would not be surprising that the ancients saw it as an ominous sign. The mass suicide of members of the hermit cult in the USA due to the appearance of the current comet is a sad reminder of those days. Modern science understands comets very well and considers them an inseparable part of the phenomena of the universe that can be accurately explained. One of the first achievements of modern astronomy was astronomer Edmund Halley's prediction of the comet that appeared in 1682. Halley determined that the comet would appear again in 1759, and this was because he realized that two "other" comets, which appeared in 1531 and 1607, were actually the same comet itself. Halley concluded that the comet (which was later named after him) was actually a type of planet, orbiting the sun in a regular cycle of 76 years. Halley's Comet did appear in 1759, returned faithfully again in 1835 and 1910 and last visited us in 1986. His last appearance was a little disappointing for viewers from Israel, but he was studied in detail by the European spacecraft Giotto, which approached him to within 600 kilometers. What does the behavior of comets mean? Why do they appear and disappear, and why are not all their appearances equal to each other? Unlike ordinary rocky planets, which are hundreds and thousands of kilometers in size, comets are made of ice and dust and are only a few kilometers in diameter. Hale-Bop is considered one of the largest and has a diameter of about forty kilometers. The orbits of comets have a very elongated oval shape, while the orbits of the regular planets are more like a circle.
Comets originate in the Oort Cloud and the Kuiper Belt - very distant clusters containing billions of comets, which are almost never seen. From time to time a single comet deviates from its distant location and "falls" towards the sun. Or then he joins about a thousand of his friends who surround him in an elliptical movement and appear before us at times. A precise observation of its orbit makes it possible to calculate the cycle time of the comet, even if it is seen here for the first time. Due to their size, the comets disappear from view when they reach the distant part of their orbit, often for periods of time much longer than a human lifetime. This explains the failure of the ancients to understand that they were cyclical planets at all. As the comet approached us (and the sun), the tiny ice ball turned into a spectacular celestial phenomenon: the sun's heat vaporizes a layer of ice and creates a glowing halo of gas and dust around the comet. The "solar wind", that constant flow of particles from the sun into space, shapes the tail from the halo, which is millions of kilometers long and is the distinct hallmark of the comet. Contrary to expectation, the tail is not trailed behind the comet in its movement, but is always directed away from the sun. Therefore, when the comet moves away from the Sun (as Hale-Bop is now doing), its tail is drawn in front of it. Hale-Bopp's photographs show two tails: one, yellowish, made of dust, and the other, bluish, made of electrically charged particles.
The comets play a complicated game with the planets next to which they pass in their orbit around the sun. Sometimes they pass closer to the earth, and then they are seen in all their glory. Other times they are more distant and barely visible, as was the case with Halley on his last pass. Small changes in their trajectory will also cause heating to one degree or another and as a result the creation of a magnificent tail, like that of a hail-bop, or a fainter one. That is why there is a degree of gambling in predicting the phenomenon of comets, and disappointed comet hunters who were not lucky and, unlike Hale and Bopp, did not get to have their progeny grace the covers of newspapers will testify to this. Sometimes the game ends in disaster: that's what happened to Comet Shoemaker-Levy, which during its first passage through the solar system disintegrated into about a dozen pieces, and then, about three years ago, collided with the planet Jupiter and came to an end in a series of huge explosions that were recorded by telescopes and satellites. It is speculated that similar cometary collisions with the Earth immediately after its formation created the primordial atmosphere, the water that currently fills the oceans and possibly also carbon compounds from which life was created. Prof. Akiva Bar Nun, a comet researcher from Tel Aviv University, contributed greatly to these discoveries. Other, later collisions may have caused catastrophes that led to the extinction of many animals on Earth (the most famous extinction, that of the dinosaurs 65 million years ago, was probably caused by an asteroid, a tiny planet made of rock, one of our closest neighbors that mostly moves between Mars to justice). Comet Hale-Bop last visited here about 4,000 years ago, and was apparently seen by Egyptian, Akkadian, and Chinese astronomers, even if there is no historical evidence for this. The next time the comet will appear "only" in a little more than 2,000 years - its cycle was shortened due to gravitational games with the planet Jupiter. Man and his culture have undergone a great change since Hale-Bop was last seen here, and opinion suggests that an equally great change will take place until his next passing near us. The appearance of the comet, which only a few would consider an ominous sign today, actually hints at man's place in the universe: a tiny and short-lived creature in vast unexplorable complexes of time and space.
