Astronomy

Astronomy is probably the oldest of the NaturalSciences. In its origins it consisted on 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, beeing 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 Star?""s, that always keep the same relative positions, and PlaneTs, that move between stars. GreeK Philosopher?""s thought of several models to explain the movements of stars, planets, the Sun? and the Moon?. The one most remembered through the Middle Ages was the geocentric model, in which the earth occupied 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 [Johannes Kepler]? and [Galileo Galilei]?.

Kepler, using precise eyeball observations made by TychoBrahe?, discovered the three laws of planetary movement that carry his name (though he published then mixed with some other not-so-correct ideas, and did'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 the SunSpot?s, but he is most famous by his problems with the CatholicChurch? (the story usually known is just a cartoon a the real thing). Galileo's greatest contribution to science was not in astronomy, but in dynamics, where he studied the motion of objects.

IsaacNewton? was the first one 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 LawOfGravity?, the LawsOfKepler? are explained, and the heliocentric system gains 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 SpectralLines? 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 ElementS? found on the sun were also found on earth.

During the 20th century SpectroMetry? (the study of these lines) advanced.

(to be continued)

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 like our own, at large distances at receiding from our own, was confirmed.