General Histories of Astronomy and Cosmology

Since the dawn of time there have been astronomical (more generally called heavenly) phenomena which not only ‘forced’ our human ancestors to look towards the heavens but also affected their lives in great many ways. To mention a few of these phenomena, one should point to the never- ending succession of night by day and vice versa, the four seasons spanning across a whole year, the bright stellar constellations covering the whole of the night sky. To be a bit more specific, the four seasons would affect the humans nutrition while the stellar constellations would facilitate navigation around the then-known world (hence increase trading and the profits made from it).

Many of the very first civilisations (Egyptians, Assyrians, etc.) glorified heavenly objects such as the sun or the moon to a point where they considered them as the upper gods in their deities’ pantheon. One of the first applications of astronomy appearing in the history of human civilisation (circa 4000-1000 BC) is the adaptation of the moon calendar to the solar year which was a bit larger than the corresponding lunar periods. This adaptation was realised for agricultural reasons. Another characteristic example of a civilisation adapting its calendar to its agricultural needs is the Jews (their calendar became solar based instead of the lunar based calendar they originally used). 
Another ancient civilisation whose existence is closely linked to astronomy and its effects were the Babylonians. Their measurements regarding appearance and disappearance of heavenly bodies and the extremely accurate position monitoring of other bright planets of our solar system (e.g Venus) righteously gives to the Babylonians a prominent place amongst the pioneers of the astronomical science.

The Assyrians on the other hand were more cruel and crude compared to the Babylonians even if these two share more or less the same time slot in human history. The Assyrians treated the sun and the moon as deities like many of the Mesopotamian people at the time, but also demonstrated a vibrant interest in astrology and not so much in astronomy. One of the primary reasons that they used a calendar was not for astronomical observations or other reasons, but for astrological predictions; Assyrians deeply believed that the effect of the stars and heavenly bodies on the behaviour and thought of the man was quite significant. What is even more interesting is that Assyrians in their effort to discover and interpret omens regarding kingdoms, kings, empires etc., observed more closely the moon and the stars rather than the sun. This ‘preference’ was due to the fact that the sun does not present any variations in his colour or trajectory throughout the time that he is observable from the earth. The planets and the moon in the dark sky on the other hand appear to have multiple trajectories (relative to the earth of course) depending on the time of year, etc. The Assyrians’ kingdom however was dismantled by a combined effort of the Babylonians and their allies in the late 7th century BC. This conquest marks a new era for the science of astronomy. No more omens are exclusively sought after in the night skies, but scientific observations and mapping efforts of the night sky and its objects is beginning to be realised. The town of Babylon itself which is the centre of this cultural and scientific revolution will pass from the hands of many conquerors…stability however is ensured throughout those transitions and this city will become the epicentre of this astronomical evolution up until the time of the deat of Alexander the Great roughly three centuries afterwards. 

However, it should not be forgotten that the main driving force behind the evolution of astronomy in Babylon were the priests who, locked inside their temple they made their observations but this situation had one inherent disadvantage: their knowledge and scientific methods are not documented anywhere; instead, the knowledge passed on from templar to templar most likely.
In the years after the decay of Babylon, the Chaldeans appear and take over further advancing the astronomical science. Greek mathematicians at the time also use for the first time elliptical coordinates systems to fully describe the motion of a planet inside space and not only on a two-dimensional area (as the Babylonian priests did up to that time). The Chaldeans created the now-famous Chaldean tables which are essentially a whole collection of various data on motion of the planets inside a 3-D elliptical world which is cut in two parts: an upper and a lower part which is smaller.

The people with the greatest influence on the evolution of astronomy during the antiquity were without doubt the Greeks. In classical plays such as the Iliad and the Odyssey, Homer clearly mentions a series of constellations and stars known at the time such as the Great Bear, Orion, etc. Some of the early settlers of Greece were also forced to migrate to the islands of the Aegean or to Asia Minor due to the harsh morphology of mainland Greece;  a side effect of this migration were the commercial bonds developed between those various towns. Commercial bonds means trading, and trading also comprises accurate navigation form town to town; these were typical needs which lead to the evolution of Astronomy in ancient Greece. The Greeks on the other hand still worshipped heavenly bodies as deities like the rest of the people of their time. Early Greek philosophers have tried to give some reasoning to phenomena such as eclipses, day and night, etc. Their reasoning however hardly had any practical value. The first to express an opinion of value was Thales who foretold within a year an actual solar eclipse. It is worth noticing at this point that a few Greek philosophers were the very first to express the opinion that the earth is of spherical shape and the moon rotates around it: they were Timaeus, Aristoteles and Plato. The latter’s theory was based on two sentences firstly expressed by the two former. The fact remains that by the 4th century BC, astronomy had evolved in Greece up to a point where for example the elliptical trajectories of individual planets were easy to be observed throughout the year; this evolution however was nothing compared to the corresponding revolution of other arts and philosophy of the time. 

In the second century A.D Ptolemy extended the idea of the ancient Greeks for the universe and he proposed a model where the earth was stationary at the center surrounded by eight spheres which carries the sun, the moon, the five know at that time planets and the stars. The planets moved on their respective spheres and the stars which were at the last and eighth sphere, would always stay at the same positions relative to each other and rotate across the sky; beyond those stars it wasn’t clear what existed. Ptolemy’s model was accurate to predict the position of the planets, while it fails to describe accurately the orbit of the moon. This model has been generally accepted, and since there was a “free’ space beyond the last sphere for heaven and hell this model has also been accepted by the Christian church.

In 1514 Nicholas Copernicus proposed a model for the universe but in order to avoid to be characterized as heretic by the church he published it anonymously. According to his model, the sun was stationary at the center and the earth and the planets where moving around it in circular motion. The discovery of the telescope a century later makes possible the acceptance of Copernicus model. The Italian astronomer Galileo Galilee observed that Juniper’s moon was orbiting around Juniper and not as according to Ptolemy’s model around the earth, while the German astronomer Johannes Kepler observed that planets move around sun in elliptical and not circular orbits. Those observations confirm Copernicus model for the universe, but the explanation for the elliptical and not circular motion of the planets came later in 1687. At this time a great publication came to life from Sir Isaac Newton who in his published work  explained the motion of the objects with time and he put mathematical expression for those, as well as defining the law of universal gravitation. According to him, each body in the universe will be attracted by any other body by a force known as gravity; this force is proportional to the mass of the bodies and inversely proportional to the square of the distance between them. Newton’s law of gravity gave proof that the orbits of the planets around the sun will be elliptical as so the orbit of the moon around the earth. The law of gravity gave a reasonable explanation on the motion of the planets but created a paradox at the same time; since gravity is an attractive force therefore will it cause the planets to collide at some point with each other? Newton argued on this by defining the universe as static and infinite; at that point, no one thought about the possibility that the universe will expand or contract, but they where trying to modify the law of gravity in order to complete the “picture”. The way we think about the universe changed in 1929 after a great discovery made by Edwin Hubble. Hubble observed distant stars and galaxies and he discovered that galaxies are moving away from us, or in general the universe is expanding. For an expanding universe there was a time where the universe was still infinitesimally dense and infinitely small, this time has been named as the Big Bang. At that point in time the general laws of physics broke down, and if there was time of the universe before the big bang, we are not able to know it since there is nothing left from them. The idea of a static universe collapsed!

The discovery of the electromagnetic theory by James Clerk Maxwell in 1865 brought the idea that light is a wave disturbance of the electromagnetic spectrum, which travels at fixed speeds. Albert Einstein introduced that in the theory of relativity in 1905, according to his theory all the laws of physics are the same independently from the speed of the observer. The law of relativity put an end to the idea of absolute time, since it confirmed both Newton’s and Maxwell’s theories. In 1915 Einstein extended his theory and produced the general theory of relativity; he found out that the universe is a four dimensional space where time is the fourth dimension, thus the space-time universe is not flat but it is curved by the disturbance which is caused by the mass of any object. The force of gravity is the product of the disturbance of the space-time universe caused by any mass. For example the mass of the sun curves the space-time domain while the earth is moving in a straight path in the space time domain it appear from earth (a three dimensional space) that is orbiting in an elliptical path. According to the law of relativity, the path of the light is affected by the wrapped space time universe; it bends its path so it doesn’t travel in straight line. When the light from a distant star passes near the sun the light is bended because of the distortion of space time universe by the mass, so for an observer on earth the star will appear in a different position in the sky, the prediction of general relativity confirmed by the observations made in 1919 measuring the position of a star during an eclipse. Before the theory of general relativity space and time was thought as static, events happening there wouldn’t have an affect on them, after 1915 things changed the universe defined as a dynamic quantity of space and time where each action taken place affects it.

Essay Bibliography

  1. A. Pannekoek, “A HISTORY OF ASTRONOMY”, Ruskin House, George Allen and Unwin Ltd.
  2. J.D. North, “ the Fontana history of Astronomy and Csmology”, Fontana Press
  3. I.D. Novikov, “Evolution of the Universe”, Cambridge University Press
  4. James Cornell and Alan P. Lightman, “ Revealing the Universe, Pediction and Proof in Astronomy”, The MIT Press
  5. S.W.Hawking, “A Brief History of Time”, Bantam Press 1988
  6. J.J.C. Smart, “Problems of Space and Time”, Macmillan Pub. Co, 1964
  7. S.F. Mason, “A History of Sciences”, Colier, 1962
  8. M. Kaku & J. Thompson, “Beyond Einstein”, Oxford University Press, 1999

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