Seemingly everything is graded and defined in the sky: galaxies, Saturn stars, planets, moons. And here it becomes clear that the edges of the concept of planet (planet) are not sharply defined, not when it comes to asteroids, not when it comes to Pluto and the Kuiper belt, and not when it comes to other solar systems. How will we treat reports of the discovery of additional planets?
9.10.2004
By: Zvi Atzmon, Galileo
hazy nebulae
It was the regular appearances of the moon that determined the date of the moon (that is, a month, which is also related to the birth of the moon, a new moon; so is month from the word moon. Of course, there were also some "weird" things, such as the band of light he called the "Milky Way", or a galaxy , and "nebulosity" whose essence as oil was ambiguous.
Including "planetary" nebulae (a misleading term in itself, and we are talking about structures in the Milky Way galaxy) as well as galaxies - the Andromeda galaxy, and the two "Magellanic Clouds" ("satellite" galaxies of the Milky Way). "Clouds" of Magellan are visible to the unaided eye, but only in the southern sky, and they were first known to Europeans in 1519, thanks to the famous Spaniard-explorer Ferdinand Magellan (Fernando de Magellan).
Ancient knowledge
There were also frightening things, such as solar and white eclipses. But the Babylonian and Chaldean priests had already learned to anticipate them with a certain degree of accuracy. These priests also served as astronomers, astrologers and advisors to the kingdom. And in China - there are Chinese records of solar eclipses as early as the third millennium BC, and as early as the 8th century BC, Chinese astronomers knew how to calculate almost exactly the times of eclipses.
And there were even less predictable phenomena: the momentary "sunrise" of meteors, the appearance of comets and supernovae. A supernova record was made by Chinese astronomers in 1054 AD, who called the "new" star (nova - from new) a "guest star". The supernova explosion recorded by the Chinese in 1054 is the source of the Cancer Nebula.
Supernova in daylight
This supernova, which created the Cancer Nebula, was so bright that it was visible even in daylight. The inhabitants of the American continent, in the regions of Arizona and New Mexico, also left a pictographic record (picture record) of the supernova of the year 1054. Chinese astronomers recorded another supernova in 1181.
Tycho Brahe made careful observations of the supernova of 1572 ("Tycho's star"). In October of 1604, a "guest star", a supernova, was again seen with the unaided eye. This supernova was documented by Chinese, Korean and European astronomers. Johannes Kepler documented it meticulously and it was called "Kepler's Star".
A permanent and eternal army
Galileo used it as an argument against the Aristotelian view, according to which the heavenly army is permanent and eternal. And here, with the invention of the telescope, the pure (almost) and permanent (almost) celestial world changed - almost overnight - its face. The precision, the telescope complicated any attempt to definitively define what a planet was, but in doing so I was ahead of the later.
In early December 1609, Galileo pointed his telescope at the moon, and discovered a world full of mountains and craters. Suddenly the moon became so "earthly". A fact that is not often mentioned is that another, remote and forgotten genius, the Englishman Thomas Harriot, preceded Galileo by a few months.
Beside the Milky Way
A short time before, Galileo pointed his telescope at a structure that has caused astonishment among many generations of human beings - the Milky Way, and discovered that it is made of individual stars. In July 1610, Galileo discovered what appeared to be "ears" attached to the planet Saturn (these are the most famous rings in the solar system), and in December of the same year he noticed the appearances (phases) of the planet Venus.
In May 1611 he saw spots on the face of the sun (Thomas Harriot preceded him in this as well), who already had good reason to agree with Copernicus that the planets, and so on in general, revolved around it. The reason was: the four satellites, moons ("the four moons of Galileo" : Io, Europa, Ganymede and Callisto), orbiting Jupiter, which he identified at the beginning of January 1610 - an explicit demonstration that not all The celestial bodies surround the earth.
rocky worlds
Apart from the sun and Venus, the planets of the solar system are accompanied by a moon or moons. The moons are rocky worlds, and in this respect they are similar to the "terrestrial" planets (the hot star, Venus, KdHA and Mars), on the one hand, and to the asteroids (which will be discussed later), on the other hand.
Indeed, the largest of the moons (Ganymede, Jupiter's moon, and Titan, Saturn's moon) are larger than the hot star-planet (and of course the smaller doubt-planet, Pluto). Furthermore, three of the moons have atmospheres: Saturn's moon Titan, Jupiter's Io, and Neptune's Triton. Io's and Triton's atmospheres are very thin, but Titan's atmosphere is even denser than that of Ea and is covered in clouds (hydrocarbon clouds, mainly methane).
Lord of the Rings Saturn
On the other hand, the small moons of the solar system actually merge with the larger lumps contained in the rings surrounding the gas-giant planets, the most prominent of which are the picturesque rings of Saturn, whose signature - although not their exact shape and essence - was discovered by Galileo.
In summary, very close to the invention of the telescope, the moon became very "earthly", the sun lost its celestial purity, an inner planet (Venus) gained appearances, and outer planets gained moons (Jupiter) or "additives" (rings; Saturn). But still a planet remains a planet, about the six days of Genesis.
The planet under the nose: Aristarchus, Copernicus, Galileo
In the sixth century BC, Pythagoras and Thales of Miletus claimed that the earth was spherical. Around 200 BC, the Greek mathematician, astronomer and geographer Eratosthenes of Alexandria calculated the diameter of KDA with impressive accuracy. Even earlier, around 280 BC s, Aristarchus of Samos claimed that Kdda is comprehensive the sun
This strange claim was forgotten for many hundreds of years, and was republished only in 1543, the year of the death of Nicolaus Copernicus (Nicolaus Copernicus), in his book "On the Rotation of the Celestial Bodies". In this book, Copernicus proposed the heliocentric theory, according to which the planets - and so on as a whole - revolve around the sun.
Died with the first copy
The book was ready and set for printing years before, but Copernicus was afraid of the wrath of the church, and it was not sent to print until the end of his life. It is said that he died a few hours after receiving the first printed copy of his book, which became an institutional foundation in our understanding of the universe.
William Herschel and George's Star: Uranus
The first planet that was discovered after it became clear that Kada is a planet orbiting the sun - as Aristarchus of Samos further claimed in the third century BC, is the seventh planet from the sun, Uranus. This "wandering star" (=planet) was discovered by one who himself wandered between music and astronomy, between Germany and England, and endless apartments and houses - Sir William (Friedrich Wilhelm) Herschel. Herschel discovered "his" planet in 1781.
Uranus is the first planet discovered through a telescope, and was not visible to humans before the development of the telescope. Since it was not known to our ancestors, it has no Hebrew name; So are Neptune, Pluto, the asteroids and the moons of the planets except for the moon that accompanies KDA, our moon.
Asteroids - "tiny planets"
Giuseppe Piazzi (1746-1826) was born in northern Italy. In his youth he joined a Catholic order and later taught mathematics in various cities in Italy. In 1780 he was invited to teach mathematics at the Palermo Academy.
Although he had no experience in astronomy, he worked to establish an observatory in Palermo - such an observatory was supposed to be the southernmost in Europe, and enjoy many clear nights throughout the year. With the establishment of the observatory, Piazzi devoted his best nights to astronomical observations in order to compile a new catalog of stars. He also did this on the first night of the 19th century, January 1801, XNUMX.
Elusive star
And behold, in the night he recognized an unknown star. The next night he was surprised to find that this star had changed its position, and a fear crept into his heart that he might have made a mistake in his observation. However, on the night of January 3rd, he realized that he was not mistaken, and that it was a heavenly gram that was not sitting in its place. His excitement was great the next night when he saw that the celestial gram he discovered continued to move in the same direction and at the same rate.
Eventually, on January 24, 1801, Piazzi sent letters to fellow astronomers and announced his discovery. He described this celestial object as an "unusual comet" - a comet without a trail, moving relatively slowly compared to comets, hinting at the possibility that it might be something "more important than a comet", in other words - an as yet unknown planet.
A star has fallen
Its location in the interval between Mars and Jupiter greatly strengthened the hypothesis that it is a planet. In April he sent a detailed report to a number of well-known astronomers, and proposed to give the celestial gram he discovered the nickname Ceres, after the patron goddess of Sicily. In March 1802, the German astronomer (and doctor by profession) Heinrich Wilhelm Olbers discovered another "tiny planet", which was nicknamed Pallas (2 Pallas).
Shortly after, William Herschel announced that these are tiny bodies compared to the planets, and proposed to call them "asteroids" (asteroids), not planets. One can understand Piazzi's disappointed heart, while Herschel continued to hold the title of "the only mortal to discover a planet" for another 44 years, until the planet Neptune was discovered. It is interesting that one of the actors in the story of the discovery of Neptune was Sir William's son, John Herschel.
Juno 3
In 1804 another asteroid was discovered by Harding (K. Harding), and was called Juno (3 Juno). In 1807, Olvers discovered another asteroid, Vesta (4 Vesta). Many thousands of asteroids are known today. Keres is much larger than the others, the second largest is Pallas and the third largest is Vesta, which was, as I recall, the fourth asteroid discovered.
Asteroids are rocky bodies that orbit the Sun; They are smaller than the planets (the mass of Ceres, the largest of the asteroids, is about 1% of that of the Moon) and larger than the meteoroids - small, very small lumps, whose entry into the atmosphere creates the well-known trails of light - the meteors, falling "stars". Millions of meteoroids enter the atmosphere every day, adding about two hundred tons of material to our Earth every day. Those few among them that survive the fiery fall through the atmosphere and hit the ground are called meteorites.
To be exact
From the common people to the forefront of science - and to women
Almost nothing is known about the family and childhood of Thomas Harriot (Harriot, also Hariot), except that his father was among the common people - a very serious "genetic" defect in class England and that he was probably born in 1560. At the age of 17, he began studying at Oxford. In 1585 he joined an expedition to explore Virginia, and when he returned he compiled a detailed report that was published (1588) as a book, the only book from the pen of this genius and discoverer, who seems to have been overlooked by the history books.
To be exact
The music of the seventh planet
Friedrich Wilhelm Herschel was born in Hanover in 1738. In his youth he learned to play music and joined, his father, the army as a musician. In 1757 he sailed to England with the aim of making a living as a musician, and indeed worked in various places as an organist, music teacher and conductor. In the summer of 1772 he went to Hanover to help his younger sister Caroline Lucrezia to emigrate, she also wanted to find a living as a musician in England; She ended up being a partner in her brother's astronomical discoveries, and continued fruitful astronomical research after his death.
The orbits of most asteroids are located in the "asteroid belt", the region between Mars and Jupiter. There are also asteroids that do not reside in the asteroid belt, including asteroids whose orbits are relatively close to the Earth. One of them is the asteroid Eros (433 Eros), which was discovered in 1898. On February 12, 2001, a spacecraft landed on Eros, the Nir-Shoemaker spacecraft (see: Rex Graham - "Close to Eros", Galileo 45).
As mentioned, the asteroids are made of rocky material, like the "terrestrial" planets (Hema, Venus, KDA and Mars), like the cores of the giant gaseous planets, and like the moons. And some of them - such as the asteroid Ida (243 Ida) - are accompanied by satellites , a kind of tiny moons; asteroids that literally "play at being planets".
Asteroid for friendly eyes
Vesta (4 Vesta) is the only asteroid that can sometimes be seen with the unaided eye. This is even though we are not the largest, nor the closest to DHA; the main reason is a high coefficient of light reflection (albedo) from the surface of this asteroid.
In any case, the fact that Vesta can be seen with the unaided eye adds to the blurring of the boundary between the planets and celestial bodies that are not considered planets. If the asteroids blur the line between what is a planet and what is not a planet, then the line between an asteroid and a meteoroid is completely arbitrary.
Neptune: the expected planet, which many missed
Great and good recognized Neptune - almost. The first of them was Galileo, who noticed it on December 28, 1612, but did not recognize it as a planet. The French astronomer Lalande noticed Neptune in May 1795, but he also did not recognize it as a planet. John Herschel - the son of - noticed it in July 1830, and considered it a Saturday star; We will return to John Herschel and his connection to Neptune later.
Neptune was seen, therefore, in observations made by astronomers, but its identification as a planet was made following mathematical calculations. One of these computers was John Couch Adams (Adams), who was occupied by discrepancies between the calculated orbit of Uranus, calculated according to Newton's laws, and its observed orbit.
What diverts Uranus
While still an undergraduate student in Cambridge, Adams tried to calculate the orbit of an unknown planet that deviates Uranus from the orbit he calculated for it. Following strenuous and prolonged calculation work, Adams gave the director of the Cambridge Observatory in September 1845 a description of the expected position of the supposed planet.
However, a series of deep scientific disagreements (the Royal Astronomer, for example, claimed that the deviations in the orbit of Uranus are not caused by another planet, but by the fact that Newton's universal law of gravitation loses its accuracy at large distances...), alongside human misunderstandings and marginal faults ( such as a lost letter), meant that the required astronomical observations were not made.
Pluto: considered the ninth planet Photo: NASA
French reinforcement
In the meantime, and independently, the French mathematician Orbe Jean-Joseph Le Verrier became interested in the problem of deviations in the orbit of Uranus. John Herschel, who was very enthusiastic about Adams' calculations, tried to interest various astronomers in the search for the "new planet", but again various failures prevented the realization of the plan.
On September 10, 1846, he gave a lecture to his colleagues and said, among other things, "We see this planet as Columbus saw America from the shores of Spain; the mathematical analysis conducted is no less convincing than direct telescopic observation." La Varia did not wait for the English to come to their senses and use lenses, and on September 18, he sent a letter to the German astronomer Johann Galle, urging him to look for a planet in the location where it should be according to his calculations.
Where is it in the catalog?
The letter reached Gala on September 23. Within half an hour (!) Galla and his assistant at the observatory in Berlin identified a star that was not marked in the catalog, and the next day they already knew clearly that it was a planet - its position changed during the day. It was the planet whose existence and position had been indicated by the calculations of La Varia, and independently by Adams.
Neptune is the eighth planet according to its distance from the Sun. But Pluto, whose orbit is much more eccentric, "cuts in" at certain times and becomes eighth - at these times Neptune is the ninth planet. Most recently it was from February 1979 to February 1999. When the news of the discovery of the "Planet of La Varia" reached England, on October 1, John Herschel urged his colleagues to direct every possible lens towards the discovered planet. This time it was already an hour to his words, and already on October 10, Neptune's large moon, Triton, was discovered.
Pluto stretches the definition and us
And here, it turned out that even Neptune's orbit does not exactly fit the calculations. Once again, a hypothesis arose regarding an unknown planet, which exerts a gravitational force that causes the deviation of the orbit, a kind of déjà vu to the story of the discovery of Neptune itself. However, many years of frantic searches ended in disappointment.
In January 1929, Clyde Tombaugh joined the "Planet X" search team. The task assigned to him was to implement a modern method for identifying objects that are not fixed in place. And finally, on February 18, 1930, a star that changed its place was discovered on the photographic plates.
Identify Pluto
In May 1930, researchers at the Magellan Observatory proposed to call the planet Pluto, a name suggested to them by the 11-year-old Ventia Barney, among the many name suggestions that flowed in from around the world. A strange and disturbing matter is the identification of Pluto. It turns out that to explain the deviations in Neptune's orbit a much more massive planet is needed - orders of magnitude more massive! – From Pluto! The calculation of the trajectory according to which they searched for a ninth planet for so many years, seems to be completely irrelevant to the discovery of Pluto. Puzzle.
In 1978, James Christy discovered Pluto's moon, and named it Charon. Although, the existence of the moon as an ark "strengthens the position" of Pluto as a planet, but in many respects it is definitely an exception in the group of planets: in terms of its structure and composition (it is not one of the terrestrial planets nor of the gaseous planets), in terms of its orbit (which "cuts" as you remember Neptune's orbit), and the inclination of its orbit.
Indeed, many astronomers tend to see Pluto as a Kuiper belt body (see below), and not "really a planet". Many astronomers regard the inclusion of Pluto in the group of planets as a historical practice and nothing, and perhaps even as a historical mistake.
Planets as a precedent
It is interesting to ponder what would have happened to the definition of the planets if the albedo (light reflection coefficient) of the asteroid Ceres had been considerably higher than its actual albedo, so high that Ceres would have been visible to the unaided eye (as the asteroid Vesta sometimes appears), so that it was already known to the ancients. In this case the ancients would have included it, without a doubt, among the planets.
In this case, almost certainly all the objects directly orbiting the Sun, which are larger than a hook, should have been called planets, including Quaoar and Sedna (Quaoar, Sedna; see below) that were discovered recently. And on the other hand, as soon as they accepted William Herschel's claim, according to which Ceres is not a planet, bodies smaller than Ceres almost immediately left all the planets. The definition of the group of planets is, for the sake of accuracy, to a considerable extent dependent on random circumstances.
I wonder what the definition of the planets would be if the light reflection coefficient of the asteroid Keres was considerably high, until it was visible to the unaided eye, so it was known to the ancients.
In any case, it is common to talk about the nine planets, and school children in English-speaking countries try to remember their order, in order to succeed in tests, with the help of "memory aids", sentences such as: My Very Educated Mother Just Showed Us Nine Planets
(Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto).
Comets and the Kuiper Belt
Comets are "dirty chunks of ice" that orbit the sun in very long orbits. As they approach the sun, some of the frozen water evaporates, thus creating the halo and the huge tail (or tails) that stretches from the comet and continues in the direction of the sun.
Since this is the case, the number of times such a "block of dirty ice" can approach the sun in its orbit and take on the familiar and impressive comet shape is limited: eventually the ice evaporates entirely, and only the "dirt" remains from the comet - rock blocks, fragments, grains and "dust" : meteoroids. When the Earth passes through such comet remnants we experience a "meteor shower".
Full of dirty ice
A huge number of "dirty ice blocks" reside in the strip that lies beyond Neptune's orbit. This strip is called the "Kuiper strip", after the Dutch-American astronomer Gerard Kuiper (Kuiper, in Dutch his name is Gerard Kuiper). As mentioned, many astronomers tend to see Pluto as not really a planet, but a body belonging to it - certainly in terms of its composition - with a Kuiper belt, as well as its moon, Charon.
Quaoar
In June 2002, Chadwick Trujillo and Michael Brown (Trujillo, Brown) discovered a large object - 1250 km in diameter, approximately the diameter of Charon (Pluto's moon), located about 1.5 billion km beyond Pluto, in the Kuiper belt area, A distance of about 42 astronomical units from the sun.
The discoverers named it Quaoar (a name that should be pronounced qua - or - war), after the god of creation in the mythology of the original inhabitants (Indians) of the Los Angeles area. No, Trujillo and Brown do not think that it is a planet (and see below), and they point out that in the Kuiper belt, small bodies have already been identified, but slightly smaller, so that it is a sequence of bodies of different sizes.
Sedna
In November 2003 another large object was identified, designated 2003 VB12 and named Sedna, after the Inuit (Eskimo) goddess of sea creatures. The diameter of Sedna is probably larger than Kuvar, and smaller than Pluto, and its distance from the Sun is three times that of Pluto, beyond the Kuiper belt, in the region known as the "inner Oort Cloud".
The Oort Cloud is a "cloud" that surrounds the Sun at a very large distance and includes a huge number of dirty ice blocks, progenitors of comets. The "cloud" is named after the Dutch astronomer Jan Hendrik Ort who hypothesized its existence in the 50s. There you have it, two Dutch astronomers (Kuyper, Ort) provide the solar system with two clusters of comets, facing each other. Compared to Qavar, Sedna is larger, much further away and its orbit around the sun is much longer.
Don't get carried away with enthusiasm
Some rushed to announce the discovery of the tenth planet in the solar system. However, this enthusiasm is far from sweeping the entire community of astronomers. Michael Brown, one of Quaver's discoverers, points out possible definitions for the planets, and the shortcomings of the historical definitions.
He proposes to define a planet in a "population definition", as follows: a planet - a body in the solar system that is more massive than all the matter contained in the other bodies near its orbit, i.e. a celestial body that is "lonely" and not part of a "population" (see link at the end). This definition is obviously quantitatively based, and it eliminates any qualitative or "essential" conception of a planet compared to other masses of matter surrounding the Sun.
Planet or not?
This definition, by the way, classifies both Quaver and Pluto as non-planets - both are part of an extensive and graded population of bodies in terms of size, the "Kuiper Belt". And regarding the workshop: according to the historical definition, since it is smaller than Pluto, it is unlikely to be called a planet.
Whereas according to the population definition he offers: due to its immense remoteness, there is very little data on its "immediate environment", on the "population" near it. But Brown starts from the premise that there is indeed a huge accumulation of objects made of ice and rock fragments, the "Oort Cloud", and that Sadna is part of this population, so he predicts that even according to his definition, Sadna will turn out not to be a planet. In the end, no matter how we examine it and define it, there is no sharp, quality line that separates a planet from other objects in the solar system. Are astrologers excited about this? i don't know
extrasolar planets
Until the 90s when you said "planet" you meant the solar system. In the meantime, dozens, over 100 planets have been discovered in other solar systems, and therefore a more general question of the definition of the planets, not necessarily in our solar system, has arisen. Because of the distance and the difficulty of observation, the vast majority of the extrasolar planets identified so far are giant planets, unlike the terrestrial planets we are familiar with (and perhaps more interesting, at least in relation to the question of the possibility of life outside the Earth).
At this point, the Working Group for Extrasolar Planets (WGESP) of the International Astronomical Organization decided not to try to arrive at an "eternal" and "cosmic" definition of a planet, but to propose working definitions, which are updated from time to time, according to the ever-growing data.
The definition is current
At this stage, the definition of planets is: objects that surround suns, where thermonuclear fusion processes take place (or objects that surround remnants of suns that have already lain down); Objects that are themselves too small to sustain such thermonuclear fusion processes, but large enough "to be considered planets in the solar system".
Here, precisely at this point, the people of the extra-solar planets are debating, therefore, the question of the minimum size. And for this it is said: Sedna (vesadna) Daraa sharp is... and for the sake of accuracy, the question is whether the proposed definition is sharp enough.
They knew Uranus, Neptune, Pluto and the edge of the solar system
