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 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 200 planets have been found around other stars, most in the
interstellar neighborhood of the Sun, but a few at great distance. This
lecture reviews the search for ExoPlanets, discussing the...
Published 12/01/06
What is a planet? Is Pluto a planet? This lecture traces the debate on
the nature of what it means to be a planet by taking an historical approach,
looking at how the question has arisen with the discovery of the asteroids and
later Pluto and the Kuiper Belt. Many of the issued raised at the 2006
IAU General Assembly meeting were raised two centuries before after the
discovery of Ceres and Pallas. We will end with the new definition of a
planet, and why Pluto is better understood as a...
Published 11/30/06
Comets are occasional visitors from the icy reaches of the outer Solar
System. This lecture discusses the orbits, structure, and properties of
comets, and introduces the "dirty snowball" model of a comet nucleus.
The end of class was a demo where I created a model of a comet nucleus
from common household and office materials. Imagine a twisted
combination of Alton Brown and Emeril Lagasse with a PhD in Astrophysics
and you get the idea. We were not able to arrange for a videographer...
Published 11/29/06
Beyond the orbit of Neptune is the realm of the icy worlds, ranging in
size from Triton, the giant moon of Neptune, and the dwarf planets Pluto
and Eris, all the way down to the nuclei of comets. 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 their orbits the...
Published 11/28/06
Asteroids are the leftover rocky materials from the formation of the
Solar System that reside mainly in a broad belt between the orbits of
Mars and Jupiter. Meteoroids are fragments of asteroids or bits of
debris from passing comets that occasionally pass through our atmosphere
as meteors, and even more rarely survive the fiery passage to reach the
ground as a meteorite. This lecture reviews the physical and dynamical
(orbital) properties of Asteroids and Meteoroids, and discusses the...
Published 11/27/06
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
physics - resonances and shepherd moons - that govern their evolution.
Recorded 2006 Nov 22 in 100 Stillman Hall on the Columbus campus of The
Ohio State University.
Published 11/22/06
Saturn is attended by a system of 56 known moons and bright, beautiful
rings. The Moon system is the focus of our attention today. Saturn has
one giant moon, Titan, which is the 2nd largest moon in the Solar
System, and the only one with a heavy atmosphere. On Titan, the
atmosphere is mostly nitrogen and methane, but the temperature and
pressure are such that methane plays the same role that water plays on
the Earth: it can be either a solid, gas, or liquid. I will review
tantalizing...
Published 11/21/06
Jupiter is surrounded by a solar system in miniature of 63 known moons.
Most (59) are tiny, irregular bodies that are a combination of captured
asteroids and comets. The 4 largest are the giant Galilean Moons: Io,
Europa, Ganymede, and Callisto. 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 of Ganymede, and frozen dirty Callisto with the most...
Published 11/20/06
Uranus and Neptune are the smallest and outermost of the 4 Jovian
planets. While superficially similar to Jupiter and Saturn, there are
substantial differences. Uranus and Neptune have smaller rocky cores
surrounded by deep, slushy ice mantles and relatively thinner hydrogen
atmospheres, quite different from the massive cores and deep metallic
hydrogen mantles of Jupiter and Saturn. We will also ask why they
appear blue, look at their internal energy and weather, and then review
the...
Published 11/16/06
Jupiter and Saturn are the largest planets in the Solar System,
and the prototype of the Jovian Gas Giant planets. This lecture
focusses on the planets themselves, looking at their composition,
atmospheres, and internal structures. We will leave discussion
of their fascinating systems of rings and moons for next week.
Recorded 2006 Nov 15 in 100 Stillman Hall on the Columbus campus
of The Ohio State University.
Published 11/15/06
Having completed our tour of the terrestrial planets, we want to step
back and compare their properties. In particular, we want to look at
the processes that drive the evolution of their surfaces, their
interiors, and their atmospheres. Recorded 2006 Nov 14 in 100 Stillman
Hall on the Columbus campus of The Ohio State University.
Published 11/14/06
Mars, fourth planet from the Sun, 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 will review the properties of Mars,
and discuss the evidences of its active past. Recorded 2006 Nov 13...
Published 11/13/06
Venus, the second planet from the Sun, is perpetually veiled behind
opaque clouds of sulfuric acid droplets atop a hot, heavy, mostly carbon
dioxide atmosphere. In size and apparent composition, however, it is a
near twin-sister of the Earth. Why is it do different? This lecture
reviews the basic properties of Venus, and examines the similarties and
differences with the Earth. Recorded 2006 Nov 9 in 100 Stillman Hall on
the Columbus campus of The Ohio State University.
Published 11/09/06
Mercury is the innermost of the planets, a hot, dead world that has been
heavily battered by impacts. This lecture reviews the basic properties
of Mercury, particularly its surface and interior. Recorded 2006 Nov 8
in 100 Stillman Hall on the Columbus campus of The Ohio State
University.
Published 11/08/06
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...
Published 11/07/06
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.
Published 11/06/06
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...
Published 11/02/06
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...
Published 11/01/06
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...
Published 10/31/06
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...
Published 10/30/06
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.
Published 10/27/06
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...
Published 10/26/06
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-...
Published 10/25/06