Episodes
A new podcast, Astronomy 141, Life in the Universe, is available
for those interested in continuing an exploration of topics in
modern astronomy.
Published 12/06/09
Are we alone in the Universe? This lecture explores the question of how
we might go about finding life on planets around other stars. Rather
than talking about speculative ideas, like the Drake Equation or SETI, I
am instead taking the approach of posing it as a problem of what to look
for among the exoplanets we have been discovering in huge numbers in the
last decade. I describe the basic requirements for life, and
how life on Earth is surprisingly tough (extremophiles). I then give a...
Published 11/30/07
Are there planets around other stars? Are there Earth-like planets
around other stars? Do any of those harbor life? Intelligent life?
We'd like to know the answers to all of these questions, and in recent
years we've made great progress towards at least answering the first.
To date, more than 260 planets have been found around more than 200
other stars, most in the interstellar neighborhood of the Sun, but a few
at great distance. This lecture reviews the search for ExoPlanets,
discussing...
Published 11/29/07
Comets are chance visitors from the icy reaches of the outer Solar
System. In this lecture I describe the properties of comets, their
historical importance, and introduce the "dirty snowball" model of a
comet nucleus. At the end of class I created a model of a comet nucleus
from common household and office materials, unfortunately I could not
arrange for a videographer in time. Recorded 2007 Nov 28 in 1000
McPherson Lab on the Columbus campus of The Ohio State University.
Published 11/28/07
Beyond the orbit of Neptune lies the realm of the icy worlds, ranging in
size from Neptune's giant moon Triton and the dwarf planets Pluto and
Eris, all the way down to the nuclei of comets a few kilometers across.
This lecture discussed the icy bodies of the Trans-Neptunian regions of
the Solar System, discussing the basic properties of Triton (the best
studied such object), Pluto, Eris, and the Kuiper Belt, introducing the
dynamical families of Trans-Neptunian Objects that record in...
Published 11/27/07
Asteroids are the leftover rocky materials from the formation of the
Solar System that reside primarily in a broad belt between the orbits of
Mars and Jupiter. This lecture reviews the physical and orbital
properties of Asteroids, and discusses the role of Jupiter and orbital
resonances in dynamically sculpting the Main Belt of Asteroids. Once
again, we see how the history of the dynamical evolution of our Solar
System is written in the orbits of its members. Recorded 2007 Nov 26 in
1000...
Published 11/26/07
All Jovian planets have rings. We are most familiar with the bright,
spectacular rings of Saturn, but the other Jovian planets have rings
systems around them. This lecture describes the different ring systems
and their properties, and discusses their origin, formation, and the
gravitational interactions - resonances, perturbations, and shepherd
moons - that govern their evolution. Recorded 2007 Nov 21 in 1000
McPherson Lab on the Columbus campus of The Ohio State University.
Published 11/21/07
Saturn is attended by a system of 60 known moons and bright, beautiful
rings. Today we will explore the moons of Saturn. Among the highlights
are Saturn's lone giant moon, Titan, the 2nd largest moon in the Solar
System and the only one with a heavy atmosphere. The atmosphere of
Titan is mostly nitrogen with a little methane, but the temperature and
pressure are such that methane plays the same role on Titan that water
plays on the Earth: it can be either a solid, gas, or liquid. ...
Published 11/20/07
Jupiter has its own personal solar system in miniature of 63 known
moons. Most are tiny, irregular bodies that are a combination of
captured asteroids and comets, but it is the 4 largest, the giant
Galilean Moons: Io, Europa, Ganymede, and Callisto, that is of greatest
interest to us in this lecture. Each is a fascinating world of its own,
with a unique history and properties: volcanically active Io, icy Europa
which may hide an ocean of liquid water beneath the surface, the grooved
terrain...
Published 11/19/07
The Ice Giants Uranus and Neptune are the outermost major planets of our
Solar System. Internally they small rocky cores surrounded by deep,
slushy ice mantles and shallow hydrogen atmospheres, quite unlike the
massive cores and deep metallic hydrogen mantles of Jupiter and Saturn.
This lecture describes their basic properties: the origin of their vivid
blue/green colors, their composition, structure, and weather. At the
end we'll contrast and compare their properties to those of the...
Published 11/15/07
The Gas Giants Jupiter and Saturn are the largest planets in the Solar
System. Internally they are deep, heavy Hydrogen/Helium atmospheres on
top of dense rock/ice cores without solid surfaces. What we see in our
telescopes are just the tops of the clouds. This lecture describes the
basic properties of the planets: their composition, atmospheres,
weather, and internal structures. Recorded 2007 Nov 14 in 1000
McPherson Lab on the Columbus campus of The Ohio State University.
Published 11/14/07
Having completed our tour of the Terrestrial Planets, we want to step
back and compare their properties. In particular, we will wi review the
processes that drive the evolution of their surfaces, their interiors,
and their atmospheres. Recorded 2007 Nov 13 in 1000 McPherson Lab on
the Columbus campus of The Ohio State University.
Published 11/13/07
Mars is a cold desert planet with a thin, dry carbon-dioxide atmosphere.
The geology of Mars, however, shows signs of an active past, with
hot-spot volcanism, and tantalizing signs of ancient water flows. While
a cold, dead desert planet today, Mars' past may have been warmer and
wetter, with liquid water during the first third of its history. This
lecture reviews the properties of Mars, and describes the evidence for
its active past. Recorded 2007 Nov 9 in 1000 McPherson Lab on...
Published 11/09/07
Venus, the second planet from the Sun, is perpetually veiled behind
opaque clouds of sulfuric acid droplets atop a hot, heavy, carbon
dioxide atmosphere. In size and apparent composition, however, it is a
near twin-sister of the Earth. Why is it do different? In this lecture
I review the basic properties of Venus, and examine the similarties and
differences with the Earth. Recorded 2007 Nov 8 in 1000 McPherson Lab on
the Columbus campus of The Ohio State University.
Published 11/08/07
Mercury, innermost of the planets, is a hot, dead world that has been
heavily battered by impacts. In this lecture I review the properties of
Mercury, its orbit, rotation, surface, and interior structure. Recorded
2007 Nov 7 in 1000 McPherson Lab on the Columbus campus of The Ohio
State University.
Published 11/07/07
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...
Published 11/06/07
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.
Published 11/05/07
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...
Published 11/01/07
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...
Published 10/31/07
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...
Published 10/30/07
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...
Published 10/29/07
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.
Published 10/26/07
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...
Published 10/25/07
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...
Published 10/24/07