UCLADepartment of Physics & Astronomy Thursday April 22, 2004 at 3:30pm Room 1200 Alexei V. Filippenko, Professor of Astronomy University of California - Berkeley Alex Filippenko received his B.A. in Physics from UC Santa Barbara in 1979, and his Ph.D. in Astronomy from Caltech in 1984. He then became a Miller Fellow at UC Berkeley, and he joined the Berkeley faculty in 1986. His primary areas of research are supernovae, active galaxies, black holes, and observationalcosmology; he has also spearheaded efforts to develop robotic telescopes. He has coauthored over 400 publications on these topics, and has won numerous awards for his research, most recently a Guggenheim Fellowship. A dedicated and enthusiastic instructor, he has won the top teaching awards at UC Berkeley, and in 1995, 2001, and 2003 he o was voted the "Best Professor" on campus in informal student polls. In 1998 he produced a 40- i lecture astronomy video course with The Teaching Company, and in 2003 he taped a 16-lecture update on recent astronomical discoveries. In 2000 he coauthored an award-winning b introductory astronomy textbook; the second edition appeared in 2003. Evidence from Type Ia Supernovae for a Decelerating, then Accelerating Universe and Dark Energy The measured distances of type Ia (hydrogen- t deficient) supernovae as a function of redshift c (z) have shown that the expansion of the Universe is currently accelerating, probably a due to the presence of repulsive dark energy (X) such as Einstein's cosmological constant r (L). Combining all of the data with existing t results from large-scale structure surveys, we find a best fit for WM and WX of 0.28 and s 0.72 (respectively), in excellent agreement with b the values (0.27 and 0.73) recently derived from WMAP measurements of the cosmic a microwave background radiation. A number of possible systematic effects (dust, supernova evolution) thus far don't seem to eliminate the need for WX > 0. Most recently, analyses of supernovae at z = 1:0 – 1:7 reveal anearly epoch of deceleration, followed by acceleration. Several groups are now in the process of measuring hundreds of supernovae with z = 0:2 – 0:8, to determine the equation of state of the dark energy, wX = P=(pc2); thus Image courtesy of NASA/STScI/Ann Feild. far, the best-fit value is wX = –1, suggesting that the dark energy may indeed be the cosmological constant or something quite similar. Refreshments immediately following in room 2-222 designed by Mary Jo Robertson.