The orbits of population I stars   I.   are confined to disk of the galaxy.   II.  are very elliptical.   III. are nearly circular.   IV. are randomly inclined to the disk of the galaxy.   a. I   b. IV   c. I & IV   d. II & IV   e. I & III

4. A binary system is composed of two identical stars orbiting each other with some period To. a) Now imagine scaling all lengths (separation between the stars and the radius of the stars) by a factor k, but keeping the density of the stars the same. By what factor does the period change? b) Now instead of scaling the lengths, scale the density by k (i.e. p → kx p). By what factor does the period change?

38.  Many RR Lyrae stars are found in open clusters in the plane of the galaxy.     True     False

The first evidence for the dark energy was that: a. galaxies in clusters are moving too rapidly for the clusters to be bound.   b. Cepheid variable stars showed that galaxies were farther away that thought.   c. the cosmic microwave background spectrum was a perfect black body.   d.Type Ia supernovae appeared dimmer than predicted by Hubble’s law.   e.Einstein’s theory of gravity predicted that the Universe should collapse.