PRESENTATION UU Fellowship of North Central Iowa Sunday, August 9, 2015 Title: Dark Matter -- What do we know? Blurb: Dark Matter is a huge mystery in Astronomy. The observational evidence will be presented, including the observations and experiments under way to understand what Dark Matter is. Bio: Sam Wormley is a retired Associate Scientist and Principal Investigator at Iowa State and a retired Adjunct Prof of Astronomy at Marshalltown Community College. Sam regularly teaches science classes for the Osher Lifelong Learning Institute (OLLI) at Iowa State and for the RaySociety at Drake University. Astronomer's Tools - Spectral lines - Doppler shift http://edu-observatory.org/olli/tobbc/Week1.html Dark Matter - Galactic Rotation rates as measured by Doppler Shift of stars and gas - Motion of Galaxies in a cluster as measured by Doppler Shift of stars and gas - Gravitational Lensing (to determine mass of a cluster of galaxies) http://apod.nasa.gov/apod/ap111221.html http://apod.nasa.gov/apod/ap140715.html http://apod.nasa.gov/apod/ap111017.html - X-Ray imagery to determine the location and density of hot gas in galactic clusters http://edu-observatory.org/olli/Hubble/Week6.html - Dark Matter Candidates http://edu-observatory.org/olli/tobbc/Week8.html Summary -- the actual observation are of electromagnetic radiation, but as you can see above can be used to measure, motion within clusters and within galaxies, and gravitation effects to measure mass.