A new podcast, Astronomy 141, Life in the Universe, is available for those interested in continuing an exploration of topics in modern astronomy.

Where are Lectures 1-4? This is a good question, and one I've gotten from many listeners. Here's the answer. Recorded 2006 Nov 27 on the Columbus campus of The Ohio State University.

Welcome to the Astronomy 162 Lecture Podcasts! This is a brief message from me explaining the podcasts, and welcoming new and old listeners. Recorded 2006 Mar 10 on the Columbus campus of The Ohio State University.

How can we search for extraterrestrial intelligence, and what are we looking for? This second part of a 2-part lecture picks up where we left off yesterday by examining SETI, the Search for ExtraTerrestrial Intelligence, and reviews what we might look for and how. We will use this as a point of departure to then briefly review where we have come and what we have learned in Astronomy 162, bringing this course to a close for Winter Quarter 2006. Recorded 2006 Mar 10 in 1008 Evans Laboratory...

Are we alone in the Universe? This is the first part of a 2-part lecture that will explore the question of life and the Universe. We will look at the conditions needed for life, and address the question of how often we expect those conditions to be satisfied in our own Galaxy. In this part, we introduce the Drake Equation and make some basic estimates. To be honest, it was supposed to be one lecture, but I ran over time and ran into the bell. Oops! Very embarrasing. Tomorrow's lecture...

Can we travel through time? This is not a frivilous, science-fiction kind of question. Certain restricted kinds of time travel are in fact allowed by classical General Relativity. This lectures takes up this question, and looks at some of the surprising answers that have been found. Recorded 2006 March 8 in 1008 Evans Laboratory on the Columbus campus of The Ohio State University.

We are not made of the same matter as most of the Universe! This surprising conclusion, that the ordinary matter we are made of (protons, neutrons, and electrons) constitute only 13% or so of the total matter in the Universe, the rest being in the form of Dark Matter. Further, this dark matter is only about 30% of the combined matter and energy density of the Universe, the remaining 70% of which appears to be a form of Dark Energy that fills the vacuum of space and acts in the present day...

How will the Sun evolve? The Sun is now a middle-aged, low-mass, Main Sequence star in a state of hydrostatic and thermal equilibrium that has consumed about half of the Hydrogen available for fusion in its core. What will its subsequent evolution be as its core runs out of Hydrogen? This lecture describes our current state of understanding of the expected evolution of the Sun, informed by a combination of state-of-the-art solar models and stellar evolution codes, and data gathered from...

What is the ultimate fate of the Universe? The ultimate fate of the Big Bang is either expansion to a maximum size followed by re-collapse (the Big Crunch) or eternal expansion into a cold, dark, disordered state (the Big Chill). Which of these is our future depends on the current density of matter and energy in the Universe, Omega0. This lecture examines our current knowledge of the matter and energy content of the Universe, which leads to the surprising discovery that we live in a...

What was the Universe like from the earliest phases immediately after the Big Bang to the present day? This lecture reviews the physics of matter, and follows the evolution of the expanding Universe from the first instants after the Big Bang, when all 4 forces of nature were unified in a single grand-unified superforce until the emergence of the visible Universe we see around us today. Recorded 2006 March 1 in 1008 Evans Laboratory on the Columbus campus of The Ohio State University.

Is there any evidence that the Universe was very hot and dense in the distant past as predicted by the Big Bang model of the expanding Universe? This lecture examines observational tests of the Big Bang Model. We have already covered expansion in the previous lecture. Today we look at Primordial Nucleosynthesis, the creation of light elements from fusion during the first 3-4 minutes of the hot phases of the Big Bang, and the Cosmic Background Radiation, the relic blackbody radiation...

The Universe today is old, cold, low-density, and expanding. If we run the expansion backwards, we will eventually find a Universe where all the matter was in one place where the density and temperature are nearly infinite. We call this hot, dense initial state of the Universe the Big Bang. This lecture introduces the Big Bang model of the expanding universe, and how the history of the Universe depends on two numbers: the curretn expansion rate (H0), and the relative density of matter...

How do we measure distances on cosmic scales? This lecture describes the rungs in the cosmic distance ladder from measuring the AU in our own Solar System out into the Hubble expansion of the universe. These distances form the basis of the measurements that let us piece together the present, past, and future history of the expanding Universe, setting the stage for next week's lectures. Recorded 2006 February 24 in 1008 Evans Laboratory on the Columbus campus of The Ohio State University.

How did we discover that the Universe is Expanding? What does it mean that it is expanding? This lecture introduces Hubble's Law, the observational evidence that the Universe is systematically expanding. As galaxies get more distant from us, the apparent speed of recession gets larger in proportion. The proportionality is the rate of expansion, called the Hubble Parameter (H0). This leads us to the idea of expanding space, and the Cosmological Redshift, which combined with the Hubble Law...

What are the implications of Relativity for the Universe? This lecture introduces the Cosmological Principle, which states that the Universe is Homogeneous and Isotropic on Large Scales. Applying this to his then-new General Relativyt, Einstein got a surprise: the Universe must either expand or contract in response to all the matter/energy that fills it, something not observed in 1917. To attempt to stabilize the Universe, he introduced a Cosmological Constant (Lambda), that was to prove...

What is gravity? Newton left that question unanswered when he formulated his inverse square law of the gravitational force, framing no hypothesis for what agency transmits gravity, only asserting it was an action at a distance. Einstein brought gravity into relativity by answering Newton's unanswered question with his General Relativity, our modern theory of gravity. In Einstein's formulation, Matter tells spacetime how to curve, and curved spacetime tells matter how to move. This...

What are space and time? To begin our exploration of the evolving Universe, we must first understand what we mean by space and time. This lecture contrasts the Newtonian view of the World, with its absolute space and absolute time, with that of Einstein, who showed that space and time were not absolute but relative constructs, and that only spacetime, unified by light, was independent of the observer. This requires such non-intuitive notions as the speed of light being the same for all...

What are Active Galaxies and Quasars? We have good reason to think that buried deep in the hearts of nearly every (?) bright galaxy is a supermassive black hole with masses of millions or even billions of times the mass of the Sun. Most, like the one in our Milky Way, are quiescent, but in about 1% of galaxies, they are fed enough matter (up to about a sun's worth per year), and light up as an Active Galactic Nucleus (AGN) that can outshine an entire galaxy full of billions of...

What happens if two galaxies collide? The average distance between bright galaxies is only about 20 times their size, so over the history of the Universe (14 Billion years), we expect that most bright galaxies will have had at least one close gravitational encounter with a neighboring galaxy. This lecture explores what happens when two galaxies undergo interactions ranging from passing tidal interactions to head-on collisions, all the way to multiple collisions and galaxy "cannibalism" in...

Galaxies are found in groups and clusters, and these are only the start of a hierarchy of cosmic structures up to the largest scales observed. This lecture introduces the properties of groups and clusters of galaxies, superclusters (clusters of clusters), and large scale structure with filaments of superclusters surrouning vast voids. We start with our Local Group, and then expand our view to encompass the depths of intergalactic space. Recorded 2006 February 14 in 1008 Evans Laboratory on...

What are the different types of galaxies? What hints can they give us as to the structure and evolution of galaxies? This lecture introduces the Hubble Classification System for galaxies, and describes the properties of each major class. This detailed overview gives us some tantalizing clues as to the formation and evolution of galaxies that will be picked up in subsequent lectures. Recorded 2006 February 13 in 1008 Evans Laboratory on the Columbus campus of The Ohio State University.

What are Spiral Galaxies? This lecture describes the basic properties of spiral galaxies, their patterns of rotation and how that lets us measure their masses, and the nature of the spiral arms as waves moving through the disk and triggering formation of new stars. Recorded 2006 February 10 in 1008 Evans Laboratory on the Columbus campus of The Ohio State University.

Andromeda is the nearest bright spiral galaxy to the Milky Way, and a near twin in terms of stellar and gas content. This lecture discusses the idea of stellar populations and chemical evolution in galaxies as determined by combining observations from within (the Milky Way) and without (Andromeda). At the end, two other features of these galaxies, their supermassive central black holes, is introduced, setting up a question to be addressed in later lectures. Recorded 2006 February 9 in 1008...

How did we come to understand that the Milky Way was just one of billions of other galaxies in a vast Universe? This lecture reviews the history of how we came to recognize that the spiral nebulae were, in fact, other milky ways like our own: vast systems of 100s of billions of stars located millions of parsecs away. The key to understanding their nature was finding the distances to the spiral nebulae compared to the size of our Galaxy. Recorded 2006 February 8 in 1008 Evans Laboratory on...