1. Finding the Galactic Center (C) Copyright 2014 - all rights reserved www.cpalms.orgwww.cpalms.org

2. Our galaxy is a collection of billions of stars arranged in a flattened disk with spiral arms. Image credit: Wikipedia (C) Copyright 2014 - all rights reserved www.cpalms.orgwww.cpalms.org

3. Astronomers locate objects in the sky using a coordinate system similar to the system of latitude and longitude we use on the surface of the Earth. (C) Copyright 2014 - all rights reserved www.cpalms.orgwww.cpalms.org

4. This system measures position north or south of a celestial equator that is an extension of the Earth’s equator into space in units of degrees. (C) Copyright 2014 - all rights reserved www.cpalms.orgwww.cpalms.org

5. It also measures position around the celestial equator in units of hours and minutes. The full 360 degree sweep of the sky is divided into 24 total hours with 1 hour of right ascension equal to 15 degrees of arc. (C) Copyright 2014 - all rights reserved www.cpalms.orgwww.cpalms.org

6. Image credit: http://wind.caspercollege.edu/~marquard/astronomy/celestial_sphere.htm (C) Copyright 2014 - all rights reserved www.cpalms.orgwww.cpalms.org

7. Globular clusters are collections of thousands of stars bound to one another by gravity. Image credit: Wikipedia (C) Copyright 2014 - all rights reserved www.cpalms.orgwww.cpalms.org

8. Several dozen of these clusters are known to orbit the center of our galaxy in a roughly spherical shape. By finding the center of these clusters, we can find the center of the Milky Way Galaxy. (C) Copyright 2014 - all rights reserved www.cpalms.orgwww.cpalms.org

9. This exactly what astronomer Harlow Shapley did in the early 19 th century. He noticed that the globular clusters of the Milky Way were very skewed toward one particular direction in the sky. Image credit: Wikipedia (C) Copyright 2014 - all rights reserved www.cpalms.orgwww.cpalms.org

10. He realised that if he could locate the center of the globular clusters, he would be able to find the center of the Milky Way Galaxy. (C) Copyright 2014 - all rights reserved www.cpalms.orgwww.cpalms.org

11. Distances to the clusters are given in units of kiloparsecs. A kiloparsec (kpc) is 1,000 parsecs with 1 parsec equal to about 3.26 light years. A light year is the distance light travels in a year. It is about 10 trillion kilometers (6 trillion miles). (C) Copyright 2014 - all rights reserved www.cpalms.orgwww.cpalms.org

12. You will plot the values of right ascension on the right ascension graph. Values are given in hours (h) and minutes (m). (C) Copyright 2014 - all rights reserved www.cpalms.orgwww.cpalms.org Right ascension graph provided by Dr. Robin Ciardullo, Penn State University

13. You will then plot the values of declination (+ or – values in degrees). (C) Copyright 2014 - all rights reserved www.cpalms.orgwww.cpalms.org Declination graph provided by Dr. Robin Ciardullo, Penn State University

14. On each graph, you will determine the “average” value. These average values of right ascension and declination will locate the center of the globular clusters and the center of the Milky Way Galaxy. (C) Copyright 2014 - all rights reserved www.cpalms.orgwww.cpalms.org