Ch 15-3,4,6,7,11 and 12
The major change that Copernicus made in the Ptolemaic system was first that he believed Earth is a planet and unlike the other scholors he believed the Earth, along with the other known planets, revolved around the sun-NOT that the planets revolved around the Earth. A few years after his death, another scholar, Tycho Brahe came along and he "designed and built pointers (not exactly telescopes yet), but they were able to measure locations of "heavenly bodies"-mostly Mars. These measurments turned out to be very precise and became his "legacy to astronomy." Brahe also had a theory about the stars and their location in the sky, which is now known as "stellar parallax". Later Galileo, with the aid of a telescope, (something the other scholors did not have), proved many ideas that Capernicus believed as well as disspelled previous beliefs of others. In the Capernican system, Venus orbits the sun, and all of the phases of Venus should be visible from Earth-he proved this to be true with his observations of the phases and the varying sizes of Venus. Then along came Newton. Newton agreed with Galileo that "the natural tendency for a moving object is to continue moving at a uniform speed and in a straight line"-this idea of "inertia" is Newton's first law of motion and the first action in regards to planetary motion. The second action would have to be something that then caused these objects to not go in a straight line out in space. He formulated that there was is a gravitational force that is abound within our solar system. I found the most interesting paragraph to be this idea: "If gravity were somehow eliminated, Earth would move in a straight line out into space and if Earth's forward motion stopped, gravity would pull it directly toward the sun." Wow!
The three materials thought to make up the planets are gases, rocks and ices. The gases are hydrogen and helium and have melthing points near absolute zero. The rocks are mostly silicate minerals and metallic iron and have melting points that exceed 700 degrees C. The ices include ammonia, methane, carbon dioxide and water-they all have different melting points. The terrestrial planets are more dense and contain mostly rocky and metallic substances, with minor amounts of ices. The Jovian planets contain large amounts of gases, ices and some rocky and metalitc materials (found mostly in their core). The fact that the Jovian planets are mostly made of gases and ice though, is why they are much less dense than the Earthlike planets.
The events that lead to the creation of the solar system are still debated today, but the most widely accepted view is that of the "Big Bang Theory". In this theory, there was a "very large explosion that sent all matter of the universe flying outward at incredible speeds." The debris cooled and condensed and became what we now know as stars and galaxies-in our galaxy, The Milky Way, is where the Earth was formed. There was some other stuff about "nebular hypothesis" and "solar nebula","planetesimals" and "protoplanets" that confused me. I don't understand if this is a seperate theory than the Big Bang or if it is in conjuction with it?
Ch 16-2,5,10,22, and 25
The most basic method of determining stellar distances is by the "stellar parallax" which is a measurment of the slight back and forth shifting of a nearby star due to the orbital motion of Earth. "The nearest stars have the largest parallax angles, whereas those of distant stars are too slight to measure." You can learn a lot about stars by its color-namely its tempurature. Blue stars are very hot, red stars are much cooler. If a star is yellow, it is hotter than a red star but not nearly as hot as blue stars. This can be seen on the HR diagram as well. A star will spend most of it's life as a main sequence star, which the HR diagram will also show you (since over 90% of the stars lie in this main sequence section.)
There are three general types of galaxies: spiral, elliptical and irregular.Spiral galaxies are obviously spiral, and if you look at one from the side you will see a bright central bulge. Spiral galaxies can have "tightly wound" or "loosely wound" arms. Some have a bright "bar" running thought them also.Our galaxy is an example of a Spiral galaxy.Elliptical galaxies (the most abundant group of galaxies), are usually smaller than spiral galaxies. They are elliptical in shape and they do not have spiral arms. Irregular galaxies do not have a symmetrical shape and the stars that are contained within these galaxies are mostly young (unlike elliptical galaxies that contain older stars and spiral galaxies that have a mix of old and new).
As I was talking about before, the Big Bang theory is the most widely recognized theory of how the earth and solar system were formed. The evidence that suggests this theory is true is the idea of an "expanding universe" (ie. all galaxies (except for the very nearest) are moving away from us.) I think a big misnomer these days is that if you are Christian you can't believe in things like the Big Bang and evolution. As a Christian , I agree with this theory in the same way I believe in evolution. I wholeheartedly agree with what science has proven to be true, but the scientists can only speculate on events that occured before the bang, no one knows that for sure. That is where my belief in God lies.
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