Astronomy 161 - Introduction to Solar System Astronomy

How did the Solar System form? This lecture examines the clues in the present-day dynamics (orbital and rotation motions) of the planets and planetary composition to the formation of the solar system. We will then describe the accretion model, where 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 are in 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 giants. The whole process took about 100 million years, and we as we explore the solar system we will look for traces of this process on the various worlds we visit. Recorded 2006 Nov 7 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

We start our exploration of the Solar System with a quick overview of its constituent parts. I will take as my starting point that Pluto, Eris, and Ceres are Dwarf Planets according to the 2006 IAU decision. This decision, which is not without controversy, will be one of the questions we will revisit during these lectures. Recorded 2006 Nov 6 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

What is the structure of the Moon, and what physical processes have shaped its surface? In this lecture we turn to our nearest celestial neighbor, the Moon, to see a world quite different than the dynamic Earth. We will discuss the surface features of the Moon (the Maria and cratered highlands), see how crater density tells us the relative ages of terrain, and look at the composition of Moon rocks returned by astronauts and robotic probes. We also discuss the interior of the Moon, and review what we know about lunar history and formation. Recorded 2006 Nov 2 in 100 Stillman Hall 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? These are the questions for today's lecture. The Earth's atmosphere is a complex, dynamic, and evolving system. We will discuss the composition and structure of the atomsphere, the nature of the different thermal layers, the Greenhouse Effect, and the Primordial Atmosphere and atmospheric evolution. This will give us a basis for comparison when we begin to examine other planetary atmospheres in future lectures. Recorded 2006 Nov 1 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

What is the structure of the Earth? What better place to begin our exploration of the Solar System then with the best-studied planet, the 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. We then discuss the crust of the Earth, which is divided into 16 tectonic plates, and explore how plate motions driven by convection in the upper mantle have shaped the visible surface of our planet over its dynamic history. Recorded 2006 Oct 31 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

How old is the Earth? This lecture reviews the idea of cyclic and linear time, since how you view time determines whether the question of the age of the Earth is even meaningful. We then review various ways people have estimated the age of the Earth, starting with historical ages that equate human history with the history of the Earth proper, and then see how various physical estimates, which do not make an appeal to human history, were made. This brings us to the technique of radioactive age dating of the oldest rocks, leading to our current best estimate of 4.5+/-0.1 Billion years for the age of our planet. Recorded 2006 Oct 30 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

Telescopes, equipped with advanced electronic cameras and spectrographs, are the primary tools of the astronomer. This lecture reviews the types of telescopes and observatory sites, and discusses radio and space telescopes, and reviews briefy the observing facilities at Ohio State. Recorded 2006 Oct 27 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

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.

How do matter and light interact? This lecture is the first of a two-part lecture on the physical basis of spectroscopy. Today we will discuss the Kelvin Absolute Temperature scale, which provides a measure of the internal energy content of matter, and Kirchoff's empirical Laws of Spectroscopy, along with the Stefan-Boltzmann Law and the Wein Law to describe the continuous emission from a blackbody. We will end by briefly describing the suggestive properties of emission- and absorption-line spectra, whose explanation in the details of atomic structure will be the topic of the next lecture. Recorded 2006 Oct 25 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.

What is Light? This lecture reviews the basic properties of light, introducing the inverse square law of brightness and the Doppler Effect. Recorded 2006 Oct 23 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 are there two high tides a day? This lecture examines another of the consequences of gravity, the twice-daily tides raised on the Earth by the Moon. Tides are a consequence of 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 strongly correlate with Lunar Phase. We also look at 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 then explore the combined effects of tidal braking of the Earth, which slows the Earth's rotation and increases the length of the day by about 23 milliseconds per century, and causes the steady Recession of the Moon, which moves 3.8cm away from Earth every year. Tidal effects are extremely important to understanding the Dynamical Evolution of many bodies in the Solar System, as we'll see time and again in the second half of the class. Recorded 2006 Oct 18 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.

What is Gravity? This lecture reviews the law of falling bodies first described by Galileo, and then Newton's explanation in terms of his Law of Universal Gravitation. Gravity is a mutually attractive force that acts 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 2006 Oct 16 in 100 Stillman Hall on the Columbus campus of The Ohio State University.