Current and upcoming courses:
Courses I've taught recently at BSC include General Astronomy, Physics
of Music, General Physics I & II, Modern Physics, Mathematical
Methods for Physics, Optical Physics,
Thermal Physics, Classical Mechanics, Electricity and Magnetism, and my
honors course, "Science, Physics, Music."
- Classical Mechanics
- Principles of Astronomy
Sea - Click for
information about former and future expeditions
"We don't give A grades for large volumes of C
- John Strohl, in memorium
Saturn and the dynamics of
plasma trapped within them. These planets are particularly
interesting because both have moons imbedded within them that
contiually spew huge amounts of material into outer space. More
detailed information can be found accompanying my publications
on the topic. Io is the innermost Galilean moon of Jupiter, and
volcanic activity makes it spew off roughly a ton of mass every second.
Once ionized, this material is swept up into a large cloud of gas that
encircles the planet and rotates with it, forming a huge, million-ton
of gas around Jupiter.
The torus is centered on Io's orbit, which is about the same size our
moon's orbit about the Earth. However, the ionized gas (called a
plasma) rotates once every ten hours, so centrifugal forces are
larger than gravity. (Just imagine the moon going around the Earth two
and a half times a day rather than once a month!) It's a really
object for study, and we are fortunate to be able to do so via
from the Earth as well as spacecraft that visit Jupiter. For more
information, see my article on the torus, The
Nebula in Our Own Backyard, which appears in the Nov/Dec 2000 issue
Astronomical Society of
One of Saturn's moon's was recently to exhibit similar behavior,
though the discovery was quite unexpected. Enceladus'
diameter is one-seventh that of Io, though their orbital radii are
similar, so the gravitational tidal forces that stress and flex Io and
heat it internally are several orders of magnitude weaker at Enceladus.
Nevertheless, on 14 July 2005, the Cassini spacecraft passed
within 150 km of Enceladus and found dramatic evidence that a huge
cloud of material is continually ejected from the surface.
These atoms and ions are dissociation products of water
molecules, hinting that there must be liquid water near Enceladus'
surface. The mechanism for maintaining such warm pockets in an
environment that would otherwise be hundreds of degress below freezing
is still under debate. However, the data provide unambigous
evidence and the photographs are breathtaking.
My role in all this was in developing a theoretical model to relate the
spatial distribution of mass loading to the deflection of plasma away
from Enceladus. Those measurements were made by the Cassini
Plasma Spectrometer (CAPS), and the analysis is described in a pair of
papers, one in Science, the other in the Journal of Geophysical
Research. (Click for a preprint of Enceladus: A significant plasma
source for Saturn’s magnetosphere, by me and Tom Hill.)
Further details of my professional history are in my curriculum
vitae, or you can go directly to my publication
list. Some pre- and reprints are available. Then there are
photos and odd stuff.
Sites with information of occasional utility
Stuff for when work becomes overwhelming: