Astronomy Colloquium

  The Nobel Prize in Physics for 2011 was awarded for the discovery that the expansion of the Universe is accelerating. Yet the physical origin of cosmic acceleration remains a mystery. The Dark Energy Survey (DES) aims to address the questions: why is the expansion speeding up? Is cosmic acceleration due to dark energy or does it require a modification of General Relativity? If dark energy, is it the energy density of the vacuum (Einstein's cosmological constant) or something else? DES is addressing these questions by measuring the history of cosmic expansion and of the growth of structure through four complementary techniques: galaxy clusters, the large-scale galaxy distribution, weak gravitational lensing, and supernovae. The DES collaboration built a new, 570-megapixel, digital camera for the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory in Chile to carry out a deep, wide-area sky survey of 300 million galaxies and a time-domain survey that will discover 3500 supernovae. I will overview the DES project, which achieved `first light' in September 2012 and which is now in its second of five survey seasons,  and describe a number of early science results.