Astronomy 161 - Introduction to Solar System Astronomy - Autumn 2007

How did the Solar System form? In this lecture I review the clues for the formation of the solar system in the present-day dynamics (orbital and rotation motions) and compositions of the planets and small bodies. I then describe the standard accretion model for solar system formation, whereby grains condense out of the primordial solar nebula, grains aggregate by collisions into planetesimals, then gravity begins to work and planetesimals grow into protoplanets. What kind of planet grows depends on where the protoplanets form within the primordial solar nebula: close to the Sun only rocky planets form, beyond the Frost Line ices and volatiles can condense out allowing the growth of the gas and ice giants. The whole process took about 100 million years, and we as we explore the solar system in subsequent lectures, we will look for traces of this process on the various worlds we visit. Recorded 2007 Nov 6 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

Welcome to the Solar System! We begin our exploration of the Solar System with an overview of the planets, moons, and small bodies that make up our home system. In this lecture I'll introduce many of the themes that will encounter many times as we go through our detailed look at the Solar System in the coming weeks. Recorded 2007 Nov 5 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

What physical processes have shaped the Moon? In this lecture, I describe the surface features of the Moon (the Maria and Highlands), how crater density tells us the relative ages of terrains, and what we have learned about Moon rocks returned by astronauts and robotic probes. I will also discuss what is known about the interior of the Moon, and review what we know about lunar history and formation. Like the Earth, the Moon gives us a useful point of comparison with bodies elsewhere in the Solar System. Recorded 2007 Nov 1 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

What is the composition and structure of the Earth's atmosphere? Why is it as warm as it is, and how did it form? Today I will describe the composition and structure of the atmosphere, the Greenhouse Effect, the Primordial Atmosphere, and Atmospheric Evolution. The Earth's atmosphere is a complex, dynamic, and evolving system, and we will use it as a point of comparison when we begin to examine other planetary atmospheres in future lectures. Recorded 2007 Oct 31 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

What is the interior structure of the Earth? We will start our exploration of the Solar System with our home planet Earth. This lecture discusses the interior structure of the Earth, introducing the idea of differentiation, how geologists map the interior of the Earth using seismic waves, and the origin of the Earth's magnetic field. I describe the basic properties of the crust of the Earth, its division into rigid tectonic plates, and describe how plate motions driven by convection in the upper mantle have shaped the visible surface of our planet over its dynamic history. Recorded 2007 Oct 30 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

How old is the Earth? In this lecture I review the ideas of cyclic and linear time, and how this determines whether or not the question of the age of the Earth is meaningful. I then review various ways people have tried to estimate the age of the Earth, starting with historical ages that equate human history with the physical history of Earth. We then look at physical estimates of the Earth's age that do not make an appeal to human history, but instead seek physical processes that play out over time to make the estimates. This brings us to a discussion of radiometric age dating techniques that use the radioactive decay of isotopes trapped in minerals to identify the oldest Earth rocks and meteorites, and hence establish a radiometric date for the formation of the Earth some 4.55+/-0.05 Billion Years ago. Recorded 2007 Oct 29 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

Telescopes outfitted with modern electronic cameras and spectrographs are astronomers' primary tools for exploring the Universe. In this lecture I review the primary types of telescopes and the best observatory sites to locate them, with a brief mention of radio and space telescopes. At the end, I give a brief review of the Ohio State's observing facilities. Recorded 2007 Oct 26 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

Why does each element have its own unique spectral signature? how doe emission lines and absorption lines arise? This lecture is the second part of a two-part exploration of matter and light, looking at how the unique spectral-line signatures of atoms are a reflection of their internal electron energy-level structures. Topics include energy level diagrams for atoms, excitation, de-excitation, and ionization. There will be a short demonstration with gas-discharge tubes and slide-mounted diffraction gratings. For podcast listeners, the last portion of the class is the demo, for which we do not unfortunately have the resources to videotape. Recorded 2007 Oct 25 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

How do matter and light interact? This lecture is the first of two that will explore the interaction between light and ordinary matter, and how we measure that with spectroscopy. This lecture introduces the idea of internal energy as quantified by the temperature on the Absolute Kelvin scale, and Kirchoff's empirical Laws of Spectroscopy. We will deal primarily with blackbody spectra emitted by hot solids or hot dense gasses or liquids, the Stefan-Boltzmann and Wien Laws, and introduce emission and absorption line spectra. The next lecture will explain how line spectra arise from atoms and molecules. Recorded 2007 Oct 24 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

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.

What is light? Most astronomical objects are too far away to measure directly. Light is the messenger of the Universe, carrying with it information about objects as near as the Moon and as far away as the most distant objects in the visible Universe. In this lecture we will review the basic properties of light, the electromagnetic spectrum, the inverse square law of brightness, and the Dopper Effect. Recorded 2007 Oct 22 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 are there two high tides a day? This lecture examines tides caused by the differences in the gravity force of the Moon from one side to the other of the Earth (stronger on the side nearest the Moon, weaker on the side farthest from the Moon). The Sun raises tides on the Earth as well, about half as strong as Moon tides, giving rise to the effect of Spring and Neap tides that correlate with Lunar Phase. We will also discuss body tides raised on the Moon by the Earth, and how that has led to Tidal Locking of the Moon's rotation, which is why the Moon always keeps the same face towards the Earth. We end with a discussion of the combined effects of tidal braking of the Earth, which slows the Earth's rotation by about 23 milliseconds per day century, and causes the steady Recession of the Moon by 3.8cm away from Earth every year. Tidal effects are extremely important to understanding the dynamical evolution of the Solar System, as we'll see time and again in the second half of the class. Recorded 2007 Oct 17 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.

What is Gravity? Starting with the properties of falling bodies first formulated by Galileo, Newton applied his three laws of motion to the problem of Universal Gravitation. Newtonian Gravity is a mutually attractive force that acts at a distance between any two massive bodies. Its strength is proportional to the product of the two masses, and inversely proportional to the square of the distance between their centers. We then compare the fall of an apple on the Earth to the orbit of the Moon, and show that the Moon is held in its orbit by the same gravity that works on the surface of the Earth. In effect, the Moon is perpetually "falling" around the Earth. Recorded 2007 Oct 15 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.