Astronomy 161 - Introduction To Solar System Astronomy

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 nort

Why do celestial objects appear to rise in the East and set in the West? How does this depend on where you are on the Earth, or the time of year? Today we set the heavens into motion, and look at the two most basic types of celestial motions. Apparent daily motions are a reflection of the daily rotation of the Earth about its axis. The apparent annual motions are a reflection of the Earth's orbit around the Sun. To describe the Sun's apparent annual motion, we introduce the Ecliptic, the Obliquity of the Ecliptic, and four special locations along the Ecliptic: the Solstices and Equinoxes. This will set the stage for much of our discussions in rest of this section. Recorded 2006 Sep 27 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 is the shape and size of the Earth? This lecture traces historical ideas about the shape of the Earth, from ancient flat-Earth models to the compelling demonstrations by Aristotle in the 3rd century BC that the Earth was a sphere. We then discuss ways people measured the size of the Earth, describing the results of Eratosthenes of Cyrene in the 2nd century BC and Claudius Ptolemy in the 2nd century AD, and their impact. Recorded 2006 Sep 25 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.

Before we can begin our exploration of astronomy, we 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. We will first re-introduce the basic metric system, explaining how these units have a physical basis. For measuring lengths in astronomy, we need to introduce two special units: the Astronomical Unit, which is used to discuss interplanetary distances, and the Light Year, used for interstellar distances. We end with a discussion of mass and weight, and the distinction draw in physical measurements that differs (a little) from everyday usage. Recorded 2006 Sep 21 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