Theory The History of Astronomy

Astronomy moved along with the human history since the highest Antiquity and it participated into the evolution which had man to pass from the age of the Paleolithics to the one of the space conquest

Fundamentals

The NGC 4911 Galaxy in the Coma Cluster. picture NASA, ESA, and E. Hallman (University of Colorado, Boulder)

Celestial luminaries and the night sky likely participated into the history of mankind since the highest antiquity. Daytime and nighttime alternance, the light provided by Moon at night or the background of the starry sky likely always served like landmarks and inspire men, their dreams or magics. First evidence of a reasoning attitude about the sky and stars are found in Lascaux, France and other Paleolithic caves as the axis are using the Sun at the summer, or Full Moon at the winter, solstices. Sceneries selves would represent constellations. Then came the Neolithics as Homo sapiens, until then a hunter-gather, now turned farmer. He thus came to be needing a regular time schedule for his agricultural works and observatories-cultual sites then appeared, like in Stonhenge, by 5,000 years ago, a large megalithic circle (which could have existed like a cultual solar site even earlier). Main centers of that farming revolution in the world, like in the Middle East, the Indus River Valley or China, at last came to amplify the move of human knowledge. Scribe-priests of Sumer, about 3,000 B.C. are seen using their astronomy -which became more accurate through instruments and maths- for astrological or religious purposes. Planets are associated to gods and mythology as the first ever numerical system allows a easier recording of data. Sumer, for that part of the world between India and Europe, may be considered the founder of astronomy. Egypt, as far as it is concerned, maybe had a more utilitarian approach, with the Nile flood calendar, nighttime time hours, or the construction of pyramids and temples. A Egyptian practice consisting into referencing a position of a star by the mean of a part of the body of astronomer's aid, like 'the center,' 'upon the right shoulder,' etc. maybe influenced later descriptions of starry constellations. As they were aligning their pyramids upon Polaris, Egyptians became aware of precession. The civilization of the Indus River valley, by 500 B.C. produced a elaborated cosmology, albeit approximate -like Sun assimilated to a burning stone- as Indians of the time of the Vedas, as they had been likely influenced by Sumer, were using astronomical data for religious rituals and they practized astrology. Indians invented the sidereal year which is based upon stellar landmarks along the yearly Earth's orbit around the Sun. China, further, is not part of that area of influence of Sumer. As its philosophical system recommends that harmony be extant between the sky, men and the Earth, astronomy thus lied at the service of such a vision. Astronomy was tasked to forecast the possible perturbations of the Celestial Harmony. Chinese astronomers-astrologers had to establish a astrology-minded calendar, to foresee the unusual astronomical events like the eclipses, comets or novae and to preserve their astronomy of any foreign influence. Four Confucianist, state astronomers kept existing until by the early 20th century as they were in charge of the horoscopes, chronics, weather forecast and eclipses, and of the calendar. At the time of the Jesuit influence, a section of Arabic astronomers was extant among the court's astronomers. Chinese astronomy also influenced Japan like, for example, in terms of the question of non regular celestial events, as constellation Orion played a most important role, giving messages about one's life or agriculture and fishing, as astronomy also was the basis to calendars and sundials and Japan also knew the Jesuit influence. Civilizations in Central America too were a other civilizational area outside the influence of Sumer. Peoples there had reached to very accurate calendars and motion calculations as the Milky Way had a major role. Venus was the goddess of war and Meso-American calendars added motion of Pleiades and some planets to the reference of the Sun

The Greeks and The Logos

A following epoch is the one of Greeks, mostly. Greek philosophers were the heirs to Sumer, and further still as Alexander the Great eventuallyconquered the East. Greeks detached astronomy, like a science, from divination, mythology or even the making of the calendar as they turned astronomy into a explanation of how stars and planets move. Plato's philosophy combined a physical view with a intellectual vision of the Cosmos, as ruled through the rules of harmony as Aristotle, building from Eudoxus, is setting the basics of a model of the solar system like a complex set of embedded spheres, whose combined moves are rendering motion of planets. That model remained the dominant one until in the European Renaissance and it also allowed accurate astronomical tables as it was improved by following philosophers through the epicycle technique, with is a smaller circle beared upon one of spheres, like with Apollonius of Perga or Hipparchus. Hipparchus measured the precession and he founded the magnitudes system. The Earth, at the time, became now considered a sphere and Aristarchus of Samos forwarded the first heliocentric model of the solar system, and Pythagoricians too, as Eratosthenes performed a precise estimation of the Earth's circumference. The acme of Greek science was attained by about 150 A.D. through Ptolemy. Ptolemy was a Greek and a astronomer, geograph and mathematician in Alexandria, Egypt. He compiled the whole knowledge of his predecessors in his 'Megale Syntaxis,' or 'Great Synthesis' and he produced planets position tables and ones for the occurrence of eclipses, and a catalog of 1,022 stars as he also elaborated a list of 48 constellations. Ancient Greeks also had sophisticated gear-controlled astronomical early computers, which remained unrivaled in accuracy and complexity until 18th-century clockmakers. After that, Romans, as far as they are concerned, mostly made few advances in terms of astronomy which they used mostly under its astrological form. Romans however are the creators of the Julian calendar, under Caesar, which had the year a length of 365 days 1/4

->The Anticythera Mechanism
The Anticythera Mechanism is a mechanism composed of dented wheels, dials, spirals, and hands which dates back to the 2nd century B.C. as it was discovered along the shores of the Greek island of Anticythera by about 1900. It may be considered a real mechanical computer, which allowed the user to the lunar phases, eclipses, the positions of planets along the Zodiac or the dates of the Panhellenic Games. It worked upon the geocentric model of Hipparchus and was making use of epicycles to render the planets' motion. It was of a sophisticated construction, with some gears with a mobile center of rotation instead of fixed. Behind the device, a spiral with 235 squares -representing the Metonic cycle- allowed to figure where the Sun and Moon were relative to the Egyptian civil calendar that the Greeks were using. That part of the computer even takes into account the adjustment to the Metonic cycle which had been worked out by Greek astronomer Callipos. The eclipse prediction was based upon Babylonian arithmetics as, by 200 B.C. Greek trigonometry was not extant. The Anticythera Mechanism is also remarkable because it was cast with bronze and its gears were accurate, with their dents of about one line only. By 2016 a team of scientists about read the major part of the original text which came with the mechanism. Albeit not a manual and more a label like those displayed in a museum, the letters just 1.2 millimeter (one twentieth of a inch) engraved into the machine mostly described what it allowed too, like a a calendar for Sun and Moon, with phases, the position of both celestial bodies in the Zodiac, and planets or predicted eclipses. Some state that it could have been a sort of philosopher's guide to the solar system and our Milky Way Galaxy, showing celestial bodies in accordance with philosophical views of the Greeks at the time. No such tools was then built during the following 1,000 years! The reading gave a better idea of what the machine might have looked like, with a inventory of all the machine's dials and what they meant. The mechanism allowed a full-blown display of planets moving through the Zodiac on the front, with pointers with small spheres representing the Sun, Moon and planets arranged in a geocentric system with circular orbits around Earth

Christian West

Lunar Craters. picture NASA/JPL/USGS

Here we come now into the western Middle Ages. The West, first, lost contact with Greek science with only summaries and simplified practical texts surviving. Astronomy then became only envisioned from a practical point of view, serving to determine religious feasts -which is 'computus'- and used by monks to set their prayers times. Views of the Antiquity, like they managed to still exist, were considered sufficient enough and not able to be improved further, at the exception of people like the Venerable Bede, or periods like the continental Carolingian Renaissance. Christian West, before all, at the time, is a agricultural world as the culture in the monasteries or cathedral schools is a one of literature and the Scriptures. Any form of evolution then just could came from the Arabs, through the Al-andalus of Spain, or Sicily. Arabs had won over the whole Byzantine East as they were a people taking their caravans along the lengthy trade roads of the deserts, or their boats unto the oceans. The Arab world too was a civilization of urban merchants who, with their practical needs, triggered that important science move. As they were dwelling at the confluence of the Byzantines and the Indians, Arabs inherited the Greek and Indian works in astronomy. At the exception of some original concepts regarding orbits or the Earth's rotation, Indians mostly invented Indian numbers which transitioned to algebra and allowed easier science research. Arabic science, as it built upon the works of Greek philosophers which had been found in the libraries of the Byzantine world, was a experimental, empiritical and quantitative one as it laid down the basis for how modern science was to work. Observatories, instruments, calendaric works, catalogs and names of stars, some advanced concepts like the Earth is a sphere or some heliocentrism were the contribution of the Arabs to astronomy. Such progresses and visions eventually came to be known in the West with Gerbert, for example, the pope in 1000 A.D. already in touch with that knowledge through Spain. That mostly was however due to the Crusades, the Reconquista which, in the 12th and 13th centuries, definitively imported the Arabic advances, with the Indian numbers, trigonometry, or the translation of the Almagest of Ptolemy. At the time, new handbooks were written in the European universities, like the 'De Sphaera Mundi' by Sacrabosco about 1230 or the Alphonsine Tables which, in 1252, at the instigation of King Alfonso X of Castilla, corrected the ones by Ptolemy. That importation of the Arabic science into the West however kept to be controled, as Aristotelism -or a science method- sustaining that, was to help to knowledge only but no to heresies. As soon as by 1260 A.D., Roger Bacon and then Oresme tended to separate science and religion as that tendency was wipped off by the Hundred Years War or the Black Pleague. Even in such a context of evolution, astronomy in the West tended to lie close to such practices like astrology, or even medicine! By the end of the Middle Ages, astronomy, in the Arab world, declined as the one of India endured some form of renewal, with a partialy heliocentric system more accurate than the one Tycho Brahe was soon to establish in Europe. Chinese, as far as they were concerned, developed celestial charts for the use of their open sea navigation and they made use of armillaries

Copernicus

With the Renaissance, then came to the West a straight Byzantine influence as brought by the Greek exiles fleeing the Turks who had successfully besieged Constantinople in 1452 A.D., a renewal of the Arabic influence as their works had also be taken with, and a period of religious questionment. That time also was that of the Portuguese explorers and the discovery of Americas by Spaniards. That, in terms of astronomy, led to the fundamental step of heliocentrism! As it is ill-known whether Nicolaus Copernicus, a Polish canon got his inspiration from some Arabic stances which had had the Aristotle's system of the spheres and epicycles made to evolve, he proposed in 1510 his heliocentric vision of the world, which he had taken back from Greek Aristarchus. According to him, that view was simply a better explanation for how motions and orbits of planets worked. Copernicus' views, albeit he took the precaution to publish them in the 'De Revolutione Orbium Coelestium' only when he was laying dying, was favourably received in Rome and discredited by the speculations of Giordano Bruno and utterances of Galileo Galilei only. Galileo Galilei, in Italy, became the first to use a optical instruments to observe celestial bodies by 1610, which confirmed the thesis of Copernicus with the phases of Venus, the moons of Jupiter, for exemple. Galileo's reasoning about bodies' fall by the Pisa Tower, which contradicted Aristotle's common sense about how two bodies of different weight were falling Earth, on the other hand, was also a discovery that that fall is accelerating with height, as the more height a body is falling from the more it gains momentum. Kepler, at last, by 1609, a Czech astronomer who had been the apprentice to Danish Tycho Brahe and using the latter's scores of data gathered in Uraniborg, a visual observatory, enounced in the 'Astronomia Nova' his three laws about planetary orbits. Bayer, a German astronomer, had the 'Uranometria' published by 1603, the first modern catalog of stars. The basis of modern astronomy thus had just been established, with the solar system, telescopes, orbits and scientific observation! Roman Catholic Church immediately confronted to those however as it was still impossible at the time to state a theory true upon the sole basis of experimentation and that one had still to hold to Christian Aristotelism, or that Reason contains truths, but no Truth, and that physics can serve to a qualitative explanation of the world only

From the Industrial Revolution to Einstein

The W.M. Keck Observatory, Atop Mauna Kea in Hawaii. picture WMKO

A following step in astronomy is linked to the history of Europe. As Chinese science had received a helping hand from the Jesuite missionaries or that India managed to maintain a independent astronomy of its own, Europe fell into struggles from which England emerged like the main power. Isaac Newton, by 1687 A.D., in his 'Philosophiae Naturalis Principia Mathematica,' demonstrated how gravity -he considered a mathematical form of remote action- allowed to demonstrate back the Keplerian Laws as he also posed the general basics which were to allow the coming Industrial Revolution. A lesser aspect of Newton, on a other hand, is that he was a numerologist, considering himself like a prophet, in concurrence with Christ. English advances too are linked at the time to the needs of its Navy, which then was conquering the oceans, with the Greenwich Observatory taking part. Astronomical discoveries, through the use of telescopes, are keeping, like the speed of light by Römer by 1676, periodic comets with Halley, by 1705, or stars proper motion as they then increased further, with the distance between Earth, Venus and the Sun, with Thomas Cook in the Pacific Ocean by 1769, the German mount by Ramsden in 1774, Uranus, a seventh planet discovered by Herschell in 1789, or the proper motion of our Sun towards constellations of Hercules and Lyra. That century of the Enlightments also forwarded the relativistic questionment of the stature of mankind, or the Earth in the Universe as they also were vulgarizing the discoveries made by astronomers or scientists. Science then had turned independent from religion. Upon those bases, will the 19th century put the techniques derived from industry to the service of astronomy, like the discovery of the Asteroid Belt, a 8th planet added with Neptune by 1846, spectrography (which was to reach a apex in 1913 with the Hertzsprung-Russel Diagram), the photography, with the first image of Moon by Draper in 1840, or the helium like the component of Sun. Next to come was the 20th century, when a new major step in astronomy occurred. Einstein demonstrated by 1915 his Special, and General Relativity theories as Max Planck founded quantum physics in 1900. Eddington, in England thought that nuclear fusion is powering stars by 1920, or Edwin Hubble, between 1923 and 1929, observed like galaxies are vast ensembles of stars which, on the other hand, are getting distant from each other. Bethe and Weizsäcker demonstrated in 1938 that heavy elements in the Universe are manufactured by stars. That Newtonian model of the solar system and gravity thus had to let room to a new cosmology, that of the thermal Big Bang and spacetime. As the Cosmos according to Newton was a giant mechanical forces and orbital horologery, which let the question of the origins into a distant blur, the one by Einstein is a cosmology bringing science until into those beginnings. Reflectors, during the 20th century, took precedence upon refractors, in terms of instruments with the 5-meter Palomar Observatory built in 1948, as the exploration of the celestial objects kept through observations conducted in wavelengths other than the visible! The radio window allowed to quasars, pulsars and the background cosmic radiation, or dark matter, galactic jets and the spiral structure of our Milky Way Galaxy. Since 1962, X-rays were into the central Galactic source, the diffuse background X-ray radiation, black holes, supernovae, relativistic jets and actives galaxies (AGNs). Gamma rays, the most recent technique in terms of radiation, opened access to GRBs, blazars and cosmic rays interaction as infrared became able to peer deep into interstellar gas clouds, protoplanetary disks or exoplanets. The 20th century, on the other hand, since 1957, entered space age as exploratory missions allowed astronomers since closer, or to the surfaces of planets in the solar system. Space telescopes are also set now in orbit, like the Hubble of the Chandra Space Telescopes. The CDD electronic imagery, as it was derived from space techniques, is now surpassing photographic plates. Most recent proponents of the multiverse, at last, a derived conception of the Universe from the Big Bang are advancing a inverted Aristotelism with that idea that a infinity of worlds had been born from the original quantum event, with completely different laws of physics each, thus forever out of reach to knowledge

As far as the history of science, generally, is concerned, one may check that classical physics was the rationalist explanation of motion, distance and transformation through motion like heat, light, gravity, fluids, motion, mechanics, forces, etc. as its working domain was the English Industrial Revolution. Both fields of electricity and magnetism, which are more related to American science, came to add, which are two force of closeness. Einstein's Relativity came to give another explanation to the fields of classical physics in terms of large scale phenomenons and objects like space-time, light's photons and cosmology. Quantum physics, on a other hand, gave the fields of physics a new explanation in terms of atom's and particles' scale like particles, forces, force transport -as it mainly applies to atomic energy. Since the 1960's at last, and likely before, progress of science generally -thus of astronomy too- owed much to research which scientists led due to Cold War's demands. The development of commercial companies in the space industry more recently added too