Finding the Galactic Center (C) Copyright all rights reserved

Our galaxy is a collection of billions of stars arranged in a flattened disk with spiral arms. Image credit: Wikipedia (C) Copyright all rights reserved

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 all rights reserved

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 all rights reserved

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 all rights reserved

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Globular clusters are collections of thousands of stars bound to one another by gravity. Image credit: Wikipedia (C) Copyright all rights reserved

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 all rights reserved

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 all rights reserved

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 all rights reserved

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 all rights reserved

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

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

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 all rights reserved