ASTRONOMY COLLOQUIUM<br>Heber D. Curtis Collegiate Professorship in Astronomy Inaugural Lecture

Early in the history of our Universe, space was smoothly filled with normal matter and dark matter. This material collapsed into galaxies and stars under the influence of gravity, and deep sky images shows the Universe filled with multitudes of galaxies, many like our own Milky Way. Common wisdom said that galaxies and clusters of galaxies accounted for most of the matter in the Universe today, but a careful census shows that galaxies are missing most of their normal matter. The search for this missing matter, and what it tells us about galaxy formation has been at the center of my work and is the topic of this lecture.