Chapter 18



18.5  Stars in many globular clusters tend to have a lower abundance of massive elements than stars in the disk of our galaxy.  Explain.

Globular clusters are large groups of old stars.  They were formed much earlier than the stars in the disk of the Milky Way, when the amount of massive elements in the gas and dust was not as high as it is today.

18.7  To observers in the Southern Hemisphere, the Large and Small Magellanic Clouds look like detached pieces of the Milky Way.  What are these "clouds" and why is it not surprising they would look so much like pieces of the Milky Way?

The LMC and SMC are dwarf galaxies orbiting the MW.  Since they are made of the same stuff as the MW is, and are about the same distance from us as the center of the MW, they look about the same.

18.10  Describe how our environment would be different and how our sky might appear of our Sun and Solar System were located:

a.  near the center of the galaxy
b.  near the center of a large globular cluster
c.  near the center of large, dense molecular cloud

a.  The sky (both night and day) would be filled with millions of bright stars and there would be a very strong source of EM radation nearby - the black hole at the center of the galaxy.  It's unlikely Earth could survive such radiation and remain as it is.  The atmosphere would probably be destroyed (and the amount of high-energy radiation reaching the surface would probably kill us).

b.  The sky (both night and day) would be filled with bright stars.  Earth wouldn't be much affected.

c.  The night sky would glow a dullish red and we wouldn't be able to see any stars.  If the cloud were dense enough, even the light from the Sun would be dimmer, cooling Earth.