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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