Astronomy, which etymologically means laws of the stars, is the science whose subject is the observation and explanation of events outside the earth. Astrophysics was born as the application of physics to the phenomena observed by astronomy, this was only possible once it was understood that the elements that made up the "celestial objects" were the same that made up the Earth, and that the same laws of physics applied. Nearly all astronomers now have a strong background in physics, and the results of observations are always put in an astrophysical context, so the distinction between astronomy and astrophysics almost doesn't exist anymore.

In the early part of its history, astronomy involved only the observation and predictions of the motions of the objects in the sky that could be seen with the naked eye. Greeks made some important contributions to astronomy, but the progress almost stopped during the middle ages, except for the work of some Arabic astronomers. The renaissance came to astronomy with the work of Copernicus, who proposed a heliocentric system. His work was defended, expanded and corrected by the likes of Galileo Galilei and Kepler. The latter of these was the first to provide a system which described correctly the details of the motion of the planets with the Sun at the centre. He didn't understand the reasons behind the laws he wrote down, however, and it was left to Newton's invention of celestial dynamics and his law of gravitation, the final explanation of the motions of the planets. Stars were found much later to be far away objects, and with the advent of spectroscopy it was proved that they were similar to our own sun, but with a range of temperatures, masses and sizes.

The existence of our Galaxy, the Milky Way, as a separate group of stars was only proven in the 20th century, along with the existence of "external" galaxies, and soon after, the expansion of the universe seen in the recession of most galaxies from us. Cosmology, a discipline that has a large intersection with astronomy, made huge advances during the 20th century, with the model of the hot big bang heavily supported by the evidence provided by astronomy and physics, such as the cosmic microwave background radiation ,Hubble's Law and cosmological abundances of elements.



Posted by: Sean    Source

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