Astronomy 161 - Introduction to Solar System Astronomy - Autumn 2007

What is ordinary matter made of? This lecture reviews the basic properties of matter from subatomic to atomic scales, introducing atomic structures, atomic number and chemical elements, isotopes, radioactivity, and half-life, ending with a brief overview of the four fundamental forces of nature: gravitation, electromagnetism, and the weak and strong nuclear forces. Recorded 2007 Oct 23 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

How do objects orbit if more than 2 massive bodies are involved? Newton's versions of Keplers 3 Laws of Planetary Motion are only strictly valid for 2 massive bodies. The Solar System, however, clearly has more than 2 massive objects within it. How do we handle this many-body problem? This lecture discusses some of the multi-body gravitational effects seen in our Solar System (and by extension elsewhere). We will describe Lagrange Points for the restricted 3-body problem and consequences like the Trojan Asteroids of Jupiter, long-range gravitational perturbations and their aid in discovering the planet Neptune, close encounters that can dramatically alter the orbits of comets and give us ways to slingshot spacecraft into the outer and inner Solar System without huge expenditures of fuel, and orbital resonances that can amplify small long-range perturbations and either stabilize or destabilize orbits. All of these effects play a role in the Dynamical Evolution of our Solar System that we will see throughout later parts of the course. Recorded 2007 Oct 18 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

Why do Kepler's Laws work? In this lecture I will describe Newton's generalization of Kepler's Laws of Planetary Motion so that they will apply to any two massive bodies orbiting around their common center of mass. I will introduce families of open and closed orbits, the circular and escape speeds, center-of-mass, conservation of angular momentum, and Newton's generalized version of Kepler's 3rd Law. The latter is a powerful tool for using orbital motions as our only way to measure the masses of astronomical objects. Recorded 2007 Oct 16 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

Copernicus, Kepler, Tycho, and Galileo together gave us a new way of looking at the motions in the heavens, but they could not explain why the planets move they way the do. It was to be the work of Isaac Newton who was to sweep away the last vestiges of the Aristotelian view of the world and replace it with with a new, vastly more powerful predictive synthesis, in which all motions, in the heavens and on the Earth, obeyed three simple, mathematical laws of motion. This lecture introduces Newton's Three Laws of Motion and their consequences. Recorded 2007 Oct 12 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

In the generation following Copernicus, the question of planetary motions was picked up by two remarkable astronomers: Tycho Brahe and Johannes Kepler. Tycho was a Danish nobleman and brilliant astronomer and instrument builder whose high precision naked-eye measurements of the stars and planets were to be the summit of pre-telescopic astronomy. Kepler was the talented German mathematician who was hired by Tycho and succeeded him after his death who was to use Tycho's data to derive his three laws of planetary motion. These laws swept away the vast complex machinery of epicycles, and provide a geometric description of planetary motions that was to set the stage for their eventual physical explanation by Isaac Newton a generation later. Recorded 2007 Oct 10 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

In 1543, Nicolaus Copernicus revived Aristarchus' Heliocentric System in an attempt to rid Ptolemy's geocentric system of the un-Aristotelian idea of the Equant. He desired to create a model of the planets that would please the mind as well as preserving appearances. Rather than reinstate the ideal of the Aristotelian World View, he was to set the stage for its overthrow after nearly 2000 years of supremacy, and within two centuries give birth to the modern world. This lecture describes the astronomical world from the end of the classical age until the birth of Copernicus, and then describes his revolutionary idea of putting the Sun, and not the Earth, at the center of the Universe. Recorded 2007 Oct 9 in 1000 McPherson Lab on the Columbus campus of The Ohio State University. NOTE: Due to a recorder malfunction, only the first 15 minutes of this lecture was recorded.

How do the planets move across the sky? This lecture discusses the motions of the 5 naked-eye planets (Mercury, Venus, Mars, Jupiter, and Saturn) as seen from the Earth. We introduce the major configurations of the planets, and then discuss their apparent retrograde motions. The apparent motions of the planets are far more complex than those of the Sun, Moon, and stars, and present a great challenge to understand. The centuries long effort to understand these motions was to give birth to modern science. Recorded 2007 Oct 4 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

What time is it? Telling time is the oldest practical application of astronomy. Today's lecture is the first of a 2-part lecture on the astronomical origins of our methods of keeping time and making calendars. This lecture reviews the divisions of the year into the solstices, equinoxes, and cross-quarter days, the division of the year into months by moon phase cycles, months into weeks, and the division of the day into hours by marking the location of the Sun in the sky Recorded 2007 Oct 2 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

What are the Phases of the Moon? This lecture introduces the Moon and describes the monthly cycle of phases. Topics include synchronous rotation, apogee and perigee, the cycle of phases, and the sidereal and synodic month. Recorded 2007 Sep 28 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

Why do celestial objects appear to rise and set every day? How does this depend on where you are on the Earth, or the time of year? In today's lecture we we set the heavens into motion and review the two most basic celestial motions. Apparent Daily Motion reflects the daily rotation of the Earth about its axis. Apparent Annual Motion reflects the Earth's annual orbit around the Sun. We introduce the Ecliptic, the Sun's apparent annual path across the Celestial Sphere, and note four special locations along the Ecliptic: the Solstices and Equinoxes. This sets the stage for many of the topics of the rest of this section. Recorded 2007 Sep 26 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

What is the shape and size of the Earth? This lecture traces historical ideas about the shape of the Earth, from ancient ideas of a Flat-Earth to Aristotle's compelling demonstrations in the 3rd century BC that the Earth was a sphere. We then discuss two famous classical measurements of the circumference of the Earth by Eratosthenes of Cyrene in the 3rd century BC and Claudius Ptolemy in the 2nd century AD. Recorded 2007 Sep 24 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

What are our units of measure in astronomy? To begin our exploration of astronomy, we first need to develop a common language for notating large numbers, and introduce the basic units of length, mass, and time that we will use throughout the quarter. This lecture is a quick review of scientific notation and the metric system. For measuring the vast distances in astronomy, we need to introduce two special units: the Astronomical Unit for interplanetary distances, and the Light Year for interstellar distances. We end with a discussion of mass and weight, and the distinction drawn in physical measurements that differs (a little) from everyday usage. Recorded 2007 Sep 20 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

Welcome to the Astronomy 161 Lecture Podcasts. This is a brief message from me explaining the podcasts, and welcoming new and old listeners. University. Lectures will begin on Wednesday, 2007 Sept 19, and run through Friday, 2007 Nov 30. New lectures will appear shortly before 6pm US Eastern Time each day there is a regular class. Recorded 2007 Sep 19 in 4037 McPherson Lab on the Columbus campus of The Ohio State University.