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Unformatted text preview: Chloe List Astronomy 100 Exam 3 Notes LECTURE 19- Our Galaxy • Our galaxy=the Milky Way • It can be seen as a band of light across the night sky • The light is the combined energy of millions of stars • Far from city lights, we can see other galaxies with the eye or small telescopes • Andromeda galaxy is the nearest galaxy like our own • The Milky Way is a spiral disk galaxy • The disk is 100,000 ly in diameter • The disk is only 1,000 ly thick • Disk contains stars, gas, and dust • Dark band you see is dust • Galaxy also has a Nuclear Bulge galactic central bulge • Bulge is 20,000 ly in diameter • Bulge also contains starts, gas, and dust • Galaxy also has a halo=spherical region around the galaxy • Halo contains globular clusters, single stars, little or no gas or dust, and dark matter • The sun is located in the disk • We are ~20,000 ly from the center • We see the disk edge on • The stars in the galaxy are composed of two distinct populations of starts o Population I Stars- younger stars, like Sun The stars contain lots of heavy elements from previous generations of stars metal-rich stars o Population II Stars- older stars These stars contain mainly H and He with a few heavy elements metal-poor stars • Stars tend to form in clusters o Collections of stars having the same age o Population I Stars form in the disk in what are called open clusters cluster of a few hundred stars Pleiades & Hyades (Taurus) are open clusters Open clusters are located in the disk o Populations II Stars are located mainly in the halo in globular clusters spherical clusters of 10 5-10 7 stars Globular clusters are typically ~30 ly across • Since stars in clusters have the same age, we can measure that age using the H-R Diagram LECTURE 20- Interstellar Medium • Star Clusters o Since stars in clusters have the same age, we can measure that age using the H-R Diagram o As stars lose H in their cores, they evolve off the Main Sequence o By observing oldest MS stars, we can tell the age of the cluster o This is called the Main Sequence Turn-off o As the cluster ages, more stars will turn-off the MS the MS unzips o By observing the MS Turn-off, we can determine the age of the cluster • Our Position in the Galaxy o The size of the galaxy and our position were determined studying clusters in the halo o Harlow shapely mapped the positions of globular clusters o In 1917 he determined that the clusters were orbiting an extremely large concentration mass about 22,000 ly from Earth o He determined correctly that this must be the center of the galaxy o He also used variable stars to determine total size of the galaxy o All matter in the Galaxy rotates around Galactic center o In the disk the material rotates differentially Differential rotation=matter near the center of the Galaxy orbits faster than matter farther away Like planets in the solar system Gravity is weaker at large distances...
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- Spring '11