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WORLD FAMOUS ASTRONOMERS

SIMO JELAČA, Ph.D.

ANAXIMANDER(611-545 BC), Greek astronomer

ANAXIMANDER, He was born in Miletus, on the island of Samos. Anaximander is an astronomer who established the first concepts of the cosmos. In addition to astronomy, he studied physics, philosophy and geometry. Before Anaximander, it was believed that the Earth rested on a support in space and had the shape of a disk, which he was the first to refute. However, he believed that the Sun, Moon and stars revolved around the Earth. Anaximander was the first to use the concept of space and claimed that there was air between the Earth, Sun, Moon and stars. However, he mistakenly thought that the stars were closer to the Earth than the Moon and that the Sun was the farthest in the universe. He made the first known map of the world and made the first sundial, with the equinoxes in Greece, as well as the solar illumination in Babylon. In the field of biology, he is a precursor to Darwin's theory of evolution.

ARISTARCHUS(310-236 BC), Greek astronomer

Aristarchus was the first to calculate the sizes of the planets and their distances in the solar planetary system. He did this using the positions of the Sun, Moon and Earth at the moments of total eclipses of the Sun and Moon. He calculated the mutual distances of the celestial bodies depending on the diameter of the Earth, and the diameter of the Earth in a very original way with the help of his device called the scaphoid and the well in Siena. Aristarchus discovered that at half the Moon's brightness, the Moon subtends an angle of exactly 90° with respect to the Sun and Earth, while the angle from the center of the Earth to the Moon and the Sun is 87° (the modern angle is believed to be 89°51'), and the angle from the center of the Sun to the Earth and the Moon is 3°. From this, he determined that the diameter of the Earth is 2.8 times the diameter of the Moon, and the diameter of the Sun is 19 times the diameter of the Moon, or 6.8 times the diameter of the Earth. Aristarchus further calculated the volumes of celestial bodies, such as spheres, and determined that the volume of the Earth is 22 times the volume of the Moon, and the volume of the Sun is 6860 times the volume of the Moon, or 312 times the volume of the Earth. In the operation "Earth's Radius", he calculated that the distance of the Moon from the Earth was equal to 81 Earth's radii, and the distance of the Earth from the Sun was equal to 1550 Earth's radii. Aristarhos was the first to argue that the Earth revolves around the Sun, following a heliocentric path, and not the other way around, from west to east. He also argued that the Sun apparently moves. Aristarchus' teachings became an integral part of science in Alexandria, where he worked from 280 to 260 BC. Aristarchus also presented the first evidence that the seasons on Earth are the result of the Earth's ecliptic (which is the angle that the Earth's equator subtends with the plane of the Earth's orbit). His calculations led him to conclude that the universe is infinite. With his works, Aristarchus surpassed Aristotle, which annoyed the Alexandrian scholars and they accused him before all of Greece. As a result, he was exiled to an unknown island in 260 BC, which is why the year of his death is not known with certainty. It is known that he became the director of the philosophical school in Athens in 264 BC. It was later confirmed that Aristarchus's system of the world was identical to that of Copernican, only he preceded Copernicus by 17.2 centuries. Unfortunately for civilization, many of Aristarchus' teachings, like many others, disappeared in the fire of the famous Alexandrian Library in 392. Our esteemed scientist Milutin Milankovic, in his work “Through the Universe and Ages”, very successfully reproduced Apollonius’ theorem on the epicyclic motion of the planets of the Solar System, in which way the motion of the so-called fixed stars moves. Therefore, the stars give the impression that they are moving in one direction, then stop and after a while move in the opposite direction. This confirmed Aristarchus’ discoveries that the stars are extremely distant from our Solar System.

According to the above-mentioned Aristarchus’ report, there is a claim that in the south of Egypt, at the site of Syene, there is a very deep well in which the Sun is reflected only once a year, exactly at noon on the longest day of the year. This means that at that time, in that place, there is no shadow of the object, due to the zenith position of the Sun. Aristarchus made a device, called a scapha (sundial), which is a regularly hollowed out hemisphere, with a central rod as a pillar and marked with meridian circles. At noon on the longest day of the year in Alexandria, he measured the length of the shadow of that rod in the scapha and from the geometric relationships of the size of the given shadow and the distance from Alexandria to Syene, which was 5000 stadia, he calculated the circumference and diameter of the Earth. In this way, Aristarchus also confirmed that Greek scientists observed, thought and calculated, and left the "paid" work to others. And this is precisely where their great genius lies. The French historian Diehem says of Aristarchus that he was not only a precursor but also the inspiration for Copernicus.

CLAUDIUS PTOLEMY (90-168 AD), Greek astronomer

CLAUDIUS PTOLEMY, Greek Claudius Ptolemy was born in Alexandria, Egypt, where he worked. Otherwise, little is known about his life. In its development, it was initially based on the interpretations of Hipparchus and Aristotle, according to which the Earth is at the center of the universe, and the planets and stars revolve around it in regular circular paths. Ptolemy's system was used after him for fourteen centuries, until Copernicus' discoveries in 1543. His system of planetary motion was based on a geocentric model of the universe. According to this model, Ptolemy made mathematical calculations of the motions of all planets and stars in the form of eighty epicyclic circles of different diameters. And since even Ptolemy, in his time, did not know that the planets move in elliptical paths, his calculations are inaccurate, but they were still the closest to the time of Copernicus. Ptolemy's work, the Great Collection of Astronomy or the Great Syntax, has been preserved in its entirety.

In the field of mathematics, Ptolemy offered the first calculations of the longitudes and latitudes of the Earth, which made it possible to display projections of spherical surfaces using maps drawn to scale. Even these first maps have many inaccuracies, the equator is too far north, and Asia is too far east. However, Ptolemy's maps encouraged the navigator Christopher Columbus to head west, expecting to discover a shorter route to Asia, by which he accidentally discovered America.

Ptolemy also dabbled in astrology, arguing that the stars have an influence on human beings, like a kind of radiation. One of Ptolemy's most important legacies is his last text, Optics, in which he gave the first descriptions of optical principles. After establishing the principle of reflection, Ptolemy began to investigate the refraction of light through water, based on empirical observations.

AL-KHWARIZMI (780-850), Uzbek mathematician, geographer, and astronomer

Al-Khwarizmi, Al-Khwarizmi was born in Khorezm (now Khiva) in Uzbekistan. His full name was Abu Jafar Muhammad ibn Musa Al-Khwarizmi. He worked in Baghdad and was the first to introduce Arabic numerals into mathematics. He is one of the most prominent mathematicians, geographers, and astronomers of the Arab world. He presented his system of calculation in the section on Calculation with Hindu Numerals. After being translated into Latin, it was accepted throughout the Western world, and even today it is considered a single global language. At the age of twenty, in 800, he founded Al-Ma'mun (House of Wisdom) in Baghdad, which housed a library with translations of famous Greek philosophers and devices for astronomical observation. Al-Khwarizmi's work Calculus with Complex Numbers and Remainders is actually an introduction to the use of arithmetic, which was later called algebra. In this work, Al-Khwarizmi was the first to introduce quadratic equations, although he expressed them only descriptively. He also introduced the concept of complex numbers (by removing negative signs, for example:

24 x″ - 8 x = 16 x″ + 4 x + 60, which gives 8 x″ - 12 x = 60, or

8 x″ - 60 = 12 x. Al-Khwarizmi is therefore considered the father of algebra, and the name Algorismi (Algorithms) is derived from his name. Al-Khwarizmi is said to have been the first to calculate sines and tangents.

In the fields of astronomy and geography, he expanded on the works of Ptolemy, applying the lines of longitude and latitude, which he drew on geographical maps, much more accurately than his predecessor.

NIKOLAUS COPERNICUS (1473-1543), Polish astronomer

NIКOLAUS COPERNICUS, Polish astronomer Copernicus, as a priest, used the church to observe the stars from its bell tower. He studied at the University of Kraków, and from 1491 to 1503, he earned his doctorate at the University of Ferrara, Italy. His epochal work on the rotation of the celestial spheres was published when he was on his deathbed. The Catholic Church opposed Copernicus's teachings and forbade their publication. As soon as it was published, the church banned it in 1543, which remained in force until 1835. Copernicus was the first to determine that the planets of the solar system revolved around the Sun, not the Earth. This overturned a concept that had been in force since Aristotle. He probably came to this conclusion based on the teachings of Aristarchus. The Catholic Church also opposed the heliocentric model of planetary motion for almost three centuries. Copernicus's sunset is with the Sun at the center of planetary motion, and the Earth revolves around the Sun for a year. He expressed his position in the work "Commentariolus" in 1510-1514. According to Copernicus, according to the theory, the Earth also rotates on its axis, taking 24 hours for one full rotation. According to this statement, the position of the stars in the sky also became clearer. Initially, Copernicus did not want to publish his work Commentariolus, but it circulated among his friends. He feared that it contradicted the understanding of the Bible. Even when the church lifted the ban on the heliocentric model of the world in 1616, the ban remained until 1835, when it was accepted worldwide. After the publication of "The Revolution of the Celestial Bodies".

GALILEO GALILEI (1564-1642), Italian scientist

Galileo was born in Pisa, Italy, where he studied medicine, which he never completed. In 1583, he noticed that the oscillation of a lamp in the cathedral lasted the same time regardless of the length of the amplitude. In 1586, he invented a hydrostatic scale for determining the relative density of bodies, and in 1610, he constructed a refracting telescope. In 1632, he published Dialogue in which he dealt with the two systems of the world, which brought him into conflict with the church and demanded that he renounce the Copernican view. He was placed under house arrest.

Galileo dealt with mathematical physics, and his most significant achievements were in the field of the laws of motion. He rejected many of Aristotle's explanations, including that heavier objects fall faster to the ground. Galileo dropped objects from the Leaning Tower of Pisa, determining that all objects fall with the same acceleration, which led to the law that all objects fall with the same speed in a vacuum. This was later confirmed by other researchers. Galileo also determined that the gravitational force of the Earth's gravity and the horizontal component act simultaneously on a thrown object, which was later defined more fully by Newton. Galileo also constructed the first pendulum clock, but it was not made until after his death.

And although various telescopes had been built before Galileo, he built his own astronomical telescope, which was truly superior for its time. With it, he was the first to discover the existence of craters and mountains on the Moon and Venus. He was also the first to discover four moons around Jupiter.

JOHANNES KEPLER(1571-1630), German astronomer and mathematician

Kepler first worked as an assistant to mathematician Tycho Brahe in Prague in 1600, and after Brahe's death in 1601, he inherited his position. In 1609, he published "Neuastronomie", in which he developed his two laws of planetary motion. In 1611, he published "Dioptrics", the first work on geometric optics. He published his third law of planetary motion in "Harmony of the Worlds" in 1619. Kepler accepted Copernican views on the universe and was a brilliant sky observer, keeping very precise notes on his observations. Based on Brahe's notes, he was the first to mathematically calculate the motion of Mars. But, having received Copernicus’s opinion that the planets rotate in regular circles, his calculations were not correct. Eight years later, he determined that the planets revolve around the Sun in elliptical paths, although the two centers of the ellipse were not very far apart, in cosmic terms of magnitude. Thus, in 1609, Kepler published his discoveries in the journal Astronomia Nova, with a crystal-clear law of the universe. In his next work, Harmonices Mundi (Sacred Harmony), he added a new law, which together constituted “Kepler’s Laws of Planetary Motion.” According to the law of planetary motion in elliptical paths, the Sun is located at one of the elliptical centers. His second law states that all planets cover equal areas in equal times, regardless of the location of their paths. This means that a planet moves faster as it approaches the Sun and slower as it moves away from it. According to Kepler's third law, the time it takes for a planet to complete one revolution around the Sun is its year. Expressed in astronomical units, this time squared is equal to the distance of a given planet from the Sun to the given planet, to the cube: a≥/T″=K. K is a constant, the same for all planets.

EDMUND HALLEY(1656-1742), English astronomer

Halley is most often remembered for the comet he discovered in 1682, which was named Halley’s Comet. Halley encouraged Newton to publish his “Principia.” He studied the occurrences and paths of comets in space and concluded that comets reappear at precisely defined intervals. According to his calculations, Halley’s Comet appears every 76 years and indeed, it reappeared in 1758, then in 1834, then in 1910 and for the last time in 1986, and its next appearance will occur in 2062. This means that Halley’s Comet can be seen only once in a human lifetime. Halley studied the orbits of twenty-three comets, which he published in 1705 in his work "Synopsis of Cometary Astronomy". He also determined that stars also have their own orbits, and calculated the nineteen-year orbit of the Moon, on the basis of which he confirmed the theory of secular acceleration, which he predicted in 1695. During 1716, he calculated the distance of the Earth from the Sun in relation to the planet Venus. He also made a map of the southern constellations in 1679. In addition to astronomy, Halley is considered the founder of geophysics, in 1686, by creating maps of the winds on the Earth, with sea currents and magnetic vibrations. He also studied the salinity of the sea and the evaporation of lakes in 1687-1694, according to which he calculated the age of the Earth. He mathematically calculated pressure as a function of altitude, thereby perfecting the barometer. He even calculated population mortality, the size of the atom, the optics of a rainbow, etc.

MILUTIN MILANKOVIĆ(1879-1958), Serbian astronomer

Milutin Milanković is a scientist whose Theory of Ice Ages was accepted in the world and confirmed by the latest cosmic research. He was born in Dalj and completed his technical studies in Vienna, as one of the best students of his generation. He worked as an engineer in Austria, distinguished himself with his constructions and some innovations, and then came to Belgrade, where he became a university professor and worked until the end of his life. He achieved works of lasting value and inscribed his name among the stars. During his orbit around the Moon, Russian scientists gave the name of Milutin Milanković to a crater on the far side of the Moon, which was adopted as international recognition. The accuracy of Milanković's calculations is the greatest confirmation of his theory, which he called the Solar Canon. He was the vice-president of the Serbian Academy of Sciences, but not well known in his own country, which he otherwise carried in a gentlemanly, quiet and dignified manner. He had a brilliant writing style. His most important works are: The Canon of the Earth's Insolation and its Application to the Problem of Ice Ages, Celestial Mechanics, History of Astronomical Science, Through the Universe and Ages, Through the Kingdom of Science, Writings from the History of Science, as well as articles, speeches, correspondence, memories, experiences and knowledge. He was an engineer by profession, and an astronomer and mathematician of exceptional quality by his works. He is also remembered as a historian of science and a witness to the development of Serbian science in the first half of the twentieth century. Milanković's work Through the Universe and Ages was first published in German in a large circulation, which distinguished him as a scientist. In this work, he takes the reader in a very interesting way through ancient Babylon, ancient Athens, to visits to Aristotle and Archimedes, through the Library of Alexandria and Cleopatra, and then through the vastness of the universe. Milanković's significant works are The Mathematical Theory of Climate, The Astronomical Calendar of Ice Ages, and The Shift of the Earth's Poles for Centuries. If Kepler's and Newton's laws of motion of celestial bodies are the first law of the universe, then Milanković's law of insolation is its second law. Milanković was the first in the world to calculate the insolation of the Earth and all the planets of the Solar System, which was confirmed to be flawlessly accurate. Milanković's mathematical theory of insolation was celebrated worldwide in 1995 as one of the greatest achievements of human creativity of the twentieth century. Milanković did not study science to earn a living, but lived to study science. Milutin Milanković combines astronomy, mathematics, physics and geophysics with literature, history and philosophy in his own unique way. He also created the most accurate calendar in the world to date. He explained Aristarchus's teaching on the motion of the planets Nekretnica, reproducing Apollonius' theorem on the epicyclic motion of the planets in the Solar System. He proved that climate change is caused by astronomical causes, therefore events on Earth occur according to the laws of the sky. He was the first in the world to apply climate theory in his research. It has been said of him, "If the value of the planet is truly determined by solar energy, then the value of Milanković's work is given by the light he transmitted to generations. If even for a moment this light illuminates our life path, Milanković has reached the goal of his journey."

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