Answer any 12 of the following 14 questions. All relevant equations have been given on the cover page (not visible in WWW version). Each is worth 8 points.
1) We've used a variety of distance determination techniques this semester, but most of them, no matter how reliable, are ultimately limited in some way. For this question, it is not sufficient to simply say "method X is limited because the objects you're observing are so far away". You must state why they are limited by distance.
2) Why do high mass stars have a blue color when we see them in a telescope? In answering this question, explain the relevant difference between high mass stars and stars like our Sun, and explain why this difference leads these stars to appear blue instead of yellow or red like other stars.
3) The Sun's corona is a region of the Sun's atmosphere with temperatures so high (upwards of a million degrees...much hotter than the 6000K surface temperature) that they often approach the temperatures found in stellar cores. One piece of evidence that tells us temperatures are so high is the presence of ions in the corona. For example, several different ions of Silicon are present, including Silicon IV (Silicon that has lost three electrons) and Silicon XII (Silicon that has lost eleven electrons).
4) Spectral line analysis of the star Taygeta shows that it has much broader spectral lines that a star nearby on the sky, Maia. List at least two possible reasons why Taygeta might have broader spectral lines, then explain in a couple of sentences what observation you would try to make in order to tell which reason has resulted in the broader lines for Taygeta.
5) On the H-R Diagram below, the location of the Sun has been marked for you. No explanations are needed for this problem, although you may wish to show your work for possible partial credit in case you mark the wrong location.
6) Binary system A and binary system B are measured spectroscopically, and the companion stars in these two edge-on systems are found to have identical orbital velocities. However, the period of system A is found to be twice as long as the period of system B.
7) As the Sun ages, its core temperature will slowly increase due to a variety of factors. This should result in small but significant changes in the Sun's envelope (the region in the Sun between the core and the surface).
8) An astronomer wants to compile a catalog of galaxies that will be a representative sample of all galaxies in the visible Universe. She can't include every galaxy in her catalog, of course, so she must limit the catalog in some way. She decides to include only those (several thousand) galaxies with radial velocities less than some reasonably large value (assume she only includes galaxies with radial velocities in the lowest 20% of all galaxies).
9) For this problem, we will assume that angular momentum (mass * size * rotation speed) is a constant throughout the entire lifetime of the Sun. When the Sun ends its time on the main sequence and starts fusing Helium in its core, it will expand to about 500 times its current size and become what we call a red giant.
10) Due to stellar evolution in the galaxy, the composition of the Milky Way's interstellar medium slowly changes over time, and this effect can be seen in the composition of stars that form from this material.
11) We estimate the density of the Universe by counting up all of the mass present (both visible and dark matter) and then dividing by the volume of the Universe, just like we would determine the density of a rock or a planet. Our best estimate for the observed density of the Universe today is that it is one-tenth the so-called "critical density".
12) For this particular problem, you may assume that there is no acceleration or deceleration of the expansion of the Universe due to gravity or any kind of cosmological constant effect (just trying to keep it simple). Today, when the Universe has an age of about 12 billion years, we can draw a Hubble relation as below. Suppose Astronomers had been alive 6 billion years ago and drawn a Hubble diagram. Would it look different? If so, show on the diagram below how it would change. If it wouldn't look different, just write "no change" on the diagram. In either case, justify your answer in 2-3 sentences.
13) In an alternate Universe, suppose the expansion of the Universe had happen much more quickly. Thus, the time at the beginning of the Universe when nucleosynthesis could have occured shrinks from about three minutes to about one minute.
14) Explain why the number of currently existing, intelligent, communicative civilizations in the galaxy depends on the average lifetime of such a civilization.