Hello, I'm Brian. And I'm Paul. And we're both astronomers here at the Australian National University. In 1998, I was part of a team that made the discovery that the expansion rate of the universe was accelerating. Our discovery implies that 70% of the universe is some mysterious substance which we call dark energy. So until Brian made that discovery, we really had no idea what 70% of the universe is made out of. Yeah, and even to this day, we still really have no idea what this dark energy is. And to be quite frank, we're not that hot on the other 30% of the universe either. Most of the rest of the universe seems something called dark matter. What is dark matter? It's dark. I can't see it in its ways or not. And that's really a winner about it. Less than 5% of the universe is made up of the atoms that we study here on Earth. There's a lot we don't understand about the universe. Such as why the universe exists at all. And why did the Big Bang happen? Who pressed the Big Bang button? And how did the stars and galaxies form right after the Big Bang 13.8 billion years ago? How did black holes get to be so enormously massive? And what are gamma ray bursts? And how did planets form? We don't even know that. In this course, we're going to explore nine of the great unsolved mysteries in astronomy. We're going to go from the Big Bang all the way to the solar system. We can't promise you any answers because no one on Earth knows the answers. The best we can hope for is a more refined form of ignorance. This is the first of four courses that make up the Australian National Universities' first-year astrophysics program. It's followed by a course on exoplanets, a course on the violent universe, and a course on cosmology. To do any of these courses, we'd expect you to have a fairly good level of high school maths and physics background. The universe is a beautiful but mysterious place. And we look forward to sharing our ignorance of it with you. Thank you.