Introduction to
Modern Astronomy

For the medieval astronomer the Universe was a small place, the Earth was the center, and events seen in the sky were assumed to be orderly and designed to benefit humanity. The only changes that were viewed appropriate were cyclic changes such as the (mostly) orderly motion of the planets on the sky or the daily travel of the sun around the heavens, for cyclic change returns one to the starting point and so is not really change at all. In Europe of the Middle Ages this belief was elevated to the level of religious dogma, and one dared challenge this worldview at considerable personal peril.

However, the Copernican revolution began a long process that changed completely our perception of the Universe and humanity's place in it. Beginning in the 16th and 17th centuries and continuing until today, scientific observations and theoretical understanding have demonstrated that the Universe is enormous, that it has existed for periods that dwarf human lifetimes, and that we do not occupy its center (there is no center) . Probably less appreciated is a change with antecedents in events observed hundreds of years ago, but that has accelerated at breathtaking pace over the last 30 years. As observational astronomy at wavelengths other than visible light (Radio-Frequency, X-Ray, Gamma-Ray, Ultraviolet, ...) has become more commonplace, we have begun to appreciate that the Universe is party to scenes of unimaginable violence.

Far from an orderly stage for stately and gentle physical processes, the Universe at various times and various places undergoes violent cataclysms releasing energy on mind boggling scales . The medieval natural philosopher would perhaps have had even greater difficulty accepting this insight than accepting the Copernican hypothesis that the Earth was not the center of the Universe, as it would have destroyed the strongly held belief that the Universe existed as a nurturing cocoon for humanity. However, it is ironic that these violent processes that on the surface seem hostile to the place of humanity in the Universe are in fact essential to the production of the present Universe. In particular, our modern understanding is that there would be no matter as we know it, no life as we know it, and no humanity to contemplate these questions, in the absence of violent processes that would, of themselves, destroy all life within countless light years.

We are in fact made up of stardust from exploded stars.

We will study how this modern worldview has come about, and survey what we have learned about the Universe, and in particular the solar system, from observational and theoretical discoveries.