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Nowadays the studies and discoveries in astronomy are endless. It 'hard to remain well behind because the knowledge and tools that scientists use are very advanced. From the scientific dossier and from international magazines we hear more and more news about the discoveries and studies made recently; we hear about robots sent to other planets like Curiosity, the rover (vehicle that can be transported to other planets or satellites thanks to a lander and that feeds on itself by means of solar panels) launched by NASA 25 November 2011 from the launch site Cape Canaveral Air Force Station in Florida and landed on Mars August 6, 2012 at 7:31. It allows to the researchers to make discoveries related to the presence or absence of life on that planet thanks to the discovery of water and rocks on the planet. But now other ambitious researches are in progress and they have as an object of study: supernovae (to trace the origins of the universe), Earth-like planets, the Sun, planets made entirely (or almost all) of water, presence of multiple universes that are touching... so we could go on forever in this list but we naturally wonder how did man get to this point, or it would be better to ask where it started and how it has moved on.
This question is apparently simple, however, we can say that astronomy has ancient origins. In fact, the megalithic constructions of the Neolithic period, according to some scholars, have an array as such to that of the stars or the seasonal cycles of the Sun. You think that even Stonehenge ("stone wall"), in the south of England, was an ancient astronomical observatory; its axis was constructed so as to be oriented in the direction of dawn in the summer solstice. These structures date back to about 10,000 years ago, but we could go even further, such as 50,000 years ago as evidenced by a cult related to the constellation Ursa Major. First, it is important to understand what has driven mankind to observe and understand the processes that govern the world around us. The first men had a strong interest, a great curiosity about his surroundings and then by necessity as by forecasting of astronomical events could mark time and carry out their activities in relation to this.
Let's start by saying that all the civilizations that have shown interest in the observation of the heavens were united by the fact that they considered this not only as something to discover and study but also to venerate. When we talk about worship, we can not forget the Egyptian civilization, because of the God Ra (identified with the Sun) or pre-Columbian civilizations, famous for the construction of temples and pyramids dedicated to the gods of the sky. But it would be simplistic to think that the astronomical knowledge of the ancient civilizations were simply related to religion. Indeed, although these civilizations are chronologically very far compared to our times, they have the knowledge and cultures very refined. The civilization to which we refer are those of the Chineses, the Mayans, the Incas, the Aztecs, the Assyrians, the Babylonians and Egyptians.
Starting from the Chinese civilization, we can say that this is famous for records of the astronomical observations from 2000 to. C. and for the development of a lunisolar calendar. Other civilizations which reached the highest level in the astronomical knowledge were pre-Columbian ones whose discoveries gave no contribution to other civilizations since remained isolated until the discovery of the American continent. Suffice it to say that these people were able to predict the period of the eclipse, the cycle of the seasons, the solstices and equinoxes. Evidence of knowledge of this level are certainly the temples, built in points perfectly aligned with the sun, and the famous Mayan calendar particularly complex and composed by three cycles.
The Assyrians and Babylonians made very big steps (disciple of Pythagoras). His theory was accepted, however, until the time of Plato through a philosophical argument that the Earth, at the center of the universe, could only be spherical because the sphere is the most perfect form for a body.
The sphericity of the Earth was further accredited by Aristotle, who pointed out that shadow that Earth casts on the moon has circular contours.
After speaking of shape, let's focus attention now on the size of our planet. The first measurement is due to Eratosthenes of Cyrene. What is surprising is the incredible precision of its measurement taking into account that he used only the math. To determine such measures this scholar considered two cities, Alexandria and Syene, located on the same meridian but with different latitude (remember moreover that he was the first to divide the Earth into meridians and parallels). Doing a proportion, Eratosthenes obtained the angle of latitude, knowing the distance between the two cities and taking into account that the solar rays arriving parallel to the Earth's surface. So he obtained the length of the circumference of the earth, which was mistaken for defects of only 600 km (In fact, today's result is of 40000 while his was of 39 400) and the diameter (12629 km, less of only about 113 km with respect to the extent today accepted).
We have to wait a long time before the heliocentric theory is accepted. As you can see we talked of accepting because the man had long realized that it was the earth revolved around the sun and not the opposite. Unfortunately, this theory was not easily accepted because it meant the collapse of all the evidence on which the man had relied for centuries.
In the fourth century. a. C. various Greek philosophers (including first of all Aristarchus) had advanced the heliocentric theory that the planets revolved around the Sun and the latter around the Earth. This hypothesis was not understood then and the heliocentric theory ended up prevailing, supported by Hipparchus, Aristotle, Ptolemy and socket universally considered certain until the Renaissance, the time when Copernicus with his theory will create a revolution.
For the men of the past was available only as an investigative tool to the naked eye, but they also made use of rudimentary tools such as, for example, the merket, the auction of Archimedes or the armillary sphere.
The first instrument was used by the Egyptians to identify the position of the stars.
The auction of Archimedes consisted of a wooden shaft used to determine the angular distance of the solar disk.
Finally the Greeks were resorted to the use of the armillary sphere (invented by Eratosthenes in 255 BC.) Which was a reproduction of the celestial sphere in which we find the equator, the ecliptic, meridians and parallels.