Astronomy 161 - Introduction to Solar System Astronomy

Why does each chemical element have its own unique spectral-line signature? How do emission- and absorption-line spectra work? This lecture is the second part of a two-part exploration of the interaction between matter and light, today discussing how the unique spectral-line signatures of atoms are a reflection of their internal electron energy-level structure. We will discuss energy level diagrams for atoms, excitation, de-excitation, and ionization, and do a short demonstration with gas-discharge tubes and slide-mounted diffraction gratings. For podcast listeners, the last portion of the class is the demo, which we do not, unfortunately, have the resources to videotape. Recorded 2006 Oct 26 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

What is Matter? This lecture reviews the nature of matter from subatomic to atomic scales, and introduces the ideas of atomic structure, atomic number (number of protons), the elements, isotopes, radioactivity, and half-life. We conclude with a brief overview of the four fundamental forces of nature: gravitation, electromatgnetic, and the strong and weak nuclear forces. Recorded 2006 Oct 24 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

How do we prove physically that the Earth rotates on its axis and revolves around the Sun? Newtonian physics was so compelling that it was mostly accepted before there were ironclad physical demonstrations of the Earth's daily rotation about its axis and annual revolution (orbit) around the Sun. This lecture reviews three of these demonstrations: the Coriolis Effect, the Foucault Pendulum, and Stellar Parallaxes. This ties up the last loose-end of the Copernican Revolution. Recorded 2006 Oct 19 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

Why do Kepler's Laws work? This lecture discusses how Newton applied his Three Laws of Motion and the Law of Universal Gravitation to the problem of orbits. Newton generalized Kepler's laws to apply to any two massive bodies orbiting around their common center of mass. We discuss these new, generalized laws of orbital motion, introducing the families of open and closed orbits, circular and escape velocity, center-of-mass, conservation of angular momentum, and how orbital mechanics is used to measure the masses of astronomical objects. Recorded 2006 Oct 17 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

The work of Copernicus, Kepler, and Galileo all contributed to a new way of looking at the motions in the heavens, but did not explain why they move that way. Enter Isaac Newton, who within a few years swept away the last vestiges of the Aristotelian view of the world and replaced with a new, powerfully 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. We are now ready, next week, to examine the role of Gravity and finally explain the orbits of the planets. Recorded 2006 Oct 13 in 100 Stillman Hall 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, the brilliant Danish astronomer whose precise measurements of the planets represented the highest expression of pre-telescope astronomy, and Johannes Kepler, the brilliant and tormented German mathematician who used Tycho's data to derive his three laws of planetary motion. These laws were to sweep away the vast complex machinery of epicycles, and provide a geometric description of planetary motions that set the stage for their eventual physical explanation by Isaac Newton a generation later. Recorded 2006 Oct 11 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

What are the origins of the Geocentric and Heliocentric models put foward to explain planetary motion? This lecture begins a new unit that will chart the rise of our modern view of the solar system by reviewing the highly influential work by Greek and Roman philosophers who elaborated the first geocentric and heliocentric models of the Solar System. We discuss the various geocentric systems from the simple crystaline spheres of Anaximander, Eudoxus, and Aristotle through the Epicyclic systems of Hipparchus and Ptolemy. We will also briefly discuss what is known of Aristarchus' mostly-lost heliocentric system, which was to so strongly influence the work of Copernicus. The ultimate expression of an epicyclic Geocentric system was that described by Claudius Ptolemy in the middle of the 2nd Century AD, and was to prevail virtually unchallenged for nearly 14 centuries. Recorded 2006 Oct 9 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

Why are there leap years? This lecture explores the astronomical origins of the calendar. We will discuss lunar and solar calendars and their hybrids in history and tradition (for example, the Islamic Lunar Calendar and the Jewish Luni-Solar Calendar), and the Julian and Gregorian Calendar reforms. Recorded 2006 Oct 4 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

Eclipses of the Sun and Moon are among the most glorious spectacles in the sky. This lectures looks at the causes and types of eclipses, and how often they occur. Recorded 2006 Oct 2 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

Why do we have different seasons? This lecture looks at the consequences of the tilt of the Earth's rotation axis relative to its orbital plane (the Obliquity of the Ecliptic) combined with the apparent annual motions of the Sun around the Ecliptic. The important factor determining whether it is hot or cold at a given location at different times in the year is "insolation": how much sunlight is spread out on the ground. This, combined with the different length of the day when the Sun as at different declinations, determines to total amount of solar heating per day, and drives the general weather. It has nothing, however, to do with how far away we are from the Sun at different times of the year. Finally, the direction of the Earth's rotation axis slowly drifts westward, taking 26,000 years to go around the sky. This "Precession of the Equinoxes" represents a tiny change that is still measureable by pre-telescopic observations, and means that at different epochs in human history there is a different north pole star, or none at all! Recorded 2006 Sep 28 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

Where are we? Where is someplace else? How do I get from here to there? These are questions we need to answer both on the Earth and in the Sky to assign a location to a place or celestial object on the surface of a sphere. We start by introducing angular units, and use them to describe the terrestrial system of latitude and longitude on the spherical Earth. We then define the Celestial Sphere, with its Celestial Equator and Poles, and begin to define an analogous coordinate system on the sky. An important wrinkle is that what part of the sky we see at any given time depends on both where we are on the Earth, and what date/time it is. This gives us the start of the coordinate system we need to begin our exploration of motions in the sky in the next lectures. Recorded 2006 Sep 26 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

What are the constellations, and how have they be named and used by many different cultures throughout human history? We will review the most basic feature of the night sky, the 6000 visible stars sprinkled about the sky, and introduce the idea of constellations, reviewing their history and uses. We'll end with a brief discussion of where stars get their names. Recorded 2006 Sep 22 in 100 Stillman Hall 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, 2006 Sept 20, and run through Friday, 2006 December 1. New lectures will appear shortly before noon US Eastern time each day there is a regular class. Recorded 2006 Sept 18 on the Columbus campus of The Ohio State