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Astronomy is probably the oldest of the Natural Sciences. In its origins it consisted of the observation and cataloging of the sky and its changes. Soon the changes in the positions of the Sun and the stars where correlated with the seasons, and Astronomy took on greater importance, being practiced mostly by priests, and shrouded in mysticism. Most, if not all, ancient civilizations measured the length of the year, with varying degrees of precision. They also noticed the difference between stars, that always keep the same relative positions, and planets, that move between stars. Greek Philosophers thought of several models to explain the movements of stars, planets, the Sun and the Moon. Hipparchus was a Greek astronomer who made a number of important contributions, including the first measurement of precession and the compilation of the first star catalog. Ptolemy later referred to this work in his important Almagest?, which had a lasting effect on astronomy up to the Rennaisance?. During the Middle Ages, astronomy, as most of the sciences, didn't advance much in Europe, and many important works could have been forgotten but for the work of scholars of the Arabic world. The Arabic world under the Islam had become a higly cultured one, and many important works of knowledge from [Ancient Greece]? were translated into Arabic, used an stored in libraries throughout the area. New works were also written, and even the name of algebra tells us about his origin. In astronomy, Arab scholars also left a legacy, that is easily seen in the names still used for most of the brilliant stars in the sky (see, e.g. Ursa Major) Meanwhile in Europe, the model from the Greeks most remembered through the Middle Ages was the geocentric model, in which the Earth was in the center of the Universe, with the Sun, Moon and planets each occupying its own concentric sphere. Stars used the outermost one. Copernicus proposed a heliocentric system, in which the Sun was in the center. The model had some flaws, and did not predict the positions of the planets better that the old Ptolemaic system (the version of the geocentric model that was most accepted), but had its supporters. Two of the most famous supporters were Johannes Kepler and Galileo Galilei. Kepler, using precise naked eye observations made by Tycho Brahe, discovered the three laws of planetary movement that carry his name (though he published them mixed with some other not-so-correct ideas, and didn't give them the importance that we do). Galilei was apparently the first one to use the telescope to observe the sky, discovering the moons of Jupiter and Sunspots, but he is most famous for his problems with the Catholic Church (the story usually told is just a cartoon of the affair). Galileo's greatest contribution to science was not in astronomy, but in dynamics, where he studied the motion of objects. Isaac Newton was the first scientist to marry physics with astronomy, discovering that the same force that causes objects to fall on earth, causes the motion of planets and the moon. Using his Law Of Gravity, the Laws of Kepler are explained, and the heliocentric system gained a sound physical basis. Newton also found out that the white light from the sun can be decomposed into its component colors, this fact is crucial for most of the 20th century research. At the end of the 19th century it was discovered that, when decomposing the light from the sun, multitude of [spectral lines]? were observed (regions where there was less or no light). Experiments with hot gases showed that the same lines could be observed in the spectra of gases, specific lines corresponding to unique elements. It was proved that the chemical elements found in the sun were also found on earth. During the 20th century spectrometry? (the study of these lines) advanced, especially because of the advent of Quantum physics, that was necessary to understand the observations. Most of our current knowledge was gained during the 20th century. With the help of the use of photography, fainter objects were observed. Our sun was found to be part of a Galaxy made by more than 10^10 stars, and the existence of other galaxies, one of the matters of [The Great Debate]? was settled by [Edwin Hubble]?, who identified the Andromeda nebula as a different galaxy, and many others at large distances and receding, moving away from out galaxy. The 20th century was an exciting time for astronomy, with each advance in instrumentation leading to a new breakthrough in the understanding of the universe. (work in progress) /Talk? |
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#REDIRECT History of astronomy |
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