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Review_for_first_Midterm

Review_for_first_Midterm - Revi ew for Midterm The mos t...

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Review for Midterm The most important concepts from each chapter that we have covered are summarized below. In addition, make sure you spend some time going over the Summaries, Review Questions, and Key Terms at the end of each chapter that we covered – a good way to do this is to work together on this with some of your classmates. The exam will be 50 minutes long, and a mix of multiple choice, word match, and fill in the blanks. Good luck with your studying! Chapter 1 – The earth in context 1. You should be aware of the Big Bang and the major evidence supporting it. Distant galaxies are uniformly red-shifted, rather than blue-shifted; this implies that they are all moving away from us. The farthest galaxies are those that are most strongly red-shifted, meaning that they are receding fastest. Extrapolation of velocities and trajectories into the past suggests that all matter in the Universe was contained in a single point, approximately 13.7 billion years ago. At that time, the Universe came into existence explosively (hence the name Big Bang); radiation from the Big Bang still can be perceived in all directions in the sky (even apparently empty space) with a radio telescope. 2. Stars, including our Sun, are nuclear fusion reactors. For most of stars’ life histories (on the order of billions of years), hydrogen atoms are fused together to form helium. Later stages in stellar evolution include fusion of helium atoms and other, heavier elements; ultimately, iron is the heaviest element that can be produced through fusion reactions within stars. 3. After their cycles of fusion are complete, large stars violently explode, forming elements heavier than iron and leaving behind a residue of diffuse nebulae, which may be recycled to form a new star at some point in the future. These explosive events are termed novas and supernovas because some have been bright enough to be seen as “new stars” in the night sky. Historically, a few supernovae have even been bright enough to be seen during daylight. 4. Our Sun is approximately 5 billion years old and is expected to continue fusing helium as it does today for about another 5 billion years. All planetary orbits are coplanar, and all planets orbit in the same direction (counterclockwise as viewed from above Earth’s north pole). These facts imply simultaneous planetary formation from a swirling nebula surrounding the Sun (the similarities in orbits would then be a natural result of conservation of angular momentum). The planets accreted from this nebula through gravitational attraction and haphazard collisions. Pluto, long considered the “ninth planet,” has recently seen its status demoted; astronomers now recognize only eight major planets in our Solar System. Pluto belongs to a group of icy and rocky bodies beyond Neptune’s orbit termed the Kuiper Belt, the origination site for numerous comets.
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