Astronomy 161 - Introduction to Solar System Astronomy - Autumn 2007

By Richard PoggeScience Education Courses Natural Sciences Astronomy

Astronomy 161 - Introduction to Solar System Astronomy - Autumn 2007 episodes

October 29, 2007 Lecture 27: Deep Time - The Age of the Earth
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.
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October 26, 2007 Lecture 26: Telescopes
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.
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October 25, 2007 Lecture 25: Measuring Light - Spectroscopy
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.
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October 24, 2007 Lecture 24: Matter and Light
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.
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October 23, 2007 Lecture 23: Worlds Within - Atoms
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.
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October 22, 2007 Lecture 22: Light the Messenger
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.
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October 18, 2007 Lecture 21: Dance of the Planets
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.
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October 17, 2007 Lecture 20: Tides
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.
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October 16, 2007 Lecture 19: Orbits
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.
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October 15, 2007 Lecture 18: The Apple and the Moon - Newtonian Gravitation
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.
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