The center of the Galaxy has been observed in near infrared (just red-ward of the the reddest color that humans can perceive) wavelengths. The stars orbit rapidly a supermassive (millions of times the mass of our Sun) black hole. Observations over several years detect stars moving around the black hole. In this module, the student measures the motion of one of the many stars in orbit around the black hole. This involves using a specialized Blender Tool to simultaneously display the star field at two times to measure the distance traveled by the star. The results are plotted in Plotter Tool and the student is asked to estimate the mass of the black hole from the measured orbital velocity.