The Limited Reign of Saturn\u27s Rings

Saturn’s rings—stretching tens of thousands of miles above its equator but no more than a few hundred yards thick—mark an ancient debris field of orbiting ice shards, the remains of a moon-sized object that strayed too close and was torn to pieces by Saturn’s intense gravitation. Astronomers have debated when the rings formed and how long they will stay in orbit. Recent observations from large, land-based telescopes and orbiting spacecraft reveal that Saturn’s rings are remarkably young and are dissipating at a rapid rate. [excerpt

Reflections in a Polished Tube

When one of us (E.B.M.) dislodged a metal tube from an electric door chime recently, she inadvertently introduced her father to an attractive and instructive optical phenomenon. Looking down the highly polished inner surface of the cylinder we could see a spot surrounded by a series of bright concentric rings. The pattern looked much like the display of fringes produced by a Fabry-Perot or Michelson interferometer, except that the rings were more evenly spaced instead of crowding together strongly near the edge of the field of view. [excerpt

The Universe on a Desktop: Observational Astronomy Simulations in the Instructional Laboratory

Though the value of hands-on learning has long been recognised by educators, it is difficult to design laboratories in astronomy classes that present realistic astrophysical techniques to undergraduate students. Unlike most other sciences, astronomy is largely observational, not experimental, and making useful observations involves expensive equipment over time scales inconvenient for pedagogy. In recent years, however, astronomy has gone almost completely digital, and the advent of large on-line databases and fast personal computers has made it possible to realistically simulate the experience of research astrophysics in the laboratory. Since 1992, Project CLEA (Contemporary Laboratory Experiences in Astronomy) has been developing computer-based exercises aimed primarily at the introductory astronomy laboratory. These exercises simulate important techniques of astronomical research using digital data and Windows-based software. Each of the nine exercises developed to date consists of software, technical guides for teachers, and student manuals for the exercises. CLEA software is used at many institutions in all the United States and over 60 countries worldwide, in a variety of settings from middle school to upper-class astronomy classes. The current design philosophy and goals of Project CLEA are discussed along with plans for future development

Larry Marschall, Professor of Physics

In this issue of Next Page, Professor of Physics Larry Marschall tells us about the many influential authors (and a musician!) who inspired everything from his career path, to his political involvement and how he raised his children

Bringing the Moon Into the Classroom

Understanding the phases of the Moon is a perennial stumbling block in introductory astronomy classes. In the film, A Private Universe, for instance, both Harvard graduates and gifted high-school students display serious misconceptions about the Moon\u27s phases, believing, among other things, that the Earth\u27s shadow on the Moon is the cause of it all. Part of the problem may stem from textbook illustrations that show a view of the Moon in orbit around the Earth with the Sun of to one side. Students have trouble converting mentally from this God\u27s eye perspective into the geocentric perspective we experience as observers on the Earth looking at the Moon. As an aid in developing this skill of visualizing the same phenomenon from different frames of reference, I have lately taken to employing video techniques in the classroom. [excerpt

Catching Shadow Bands

Even though shadow bands are only visible for a few fleeting minutes, it is possible to catch them if you prepare in advance. Get a large piece of white cardboard or white-painted plywood to act as a screen--the bands are subtle and can be more easily seen against a clean, white surface. (excerpt

A Cosmic Clock for the Classroom

Teachers who watched the first episode of Carl Sagan\u27s Cosmos show on the Public Broadcasting System may have been impressed by his use of the Cosmic Calendar to dramatically introduce the evolutionary time scale of the universe. In this calendar, which Sagan first represented in The Dragons of Eden, the 15 billion year history of the universe is compressed into a single year. Each month represents 1.25 billion years, each day 40 billion years, and each second 500 years. At this scale the entire recorded history of mankind flashes by during the final 10 seconds of the cosmic year. [excerpt

Milky Way Morphology

From our limited perspective—living on a planet that orbits one of several hundred billion stars inside the Milky Way—the detailed structure of our home galaxy is difficult to determine. It has long been recognized by astronomers as a typical spiral galaxy, one of countless flattened pinwheels of stars seen throughout the universe. By mapping the distances to more than 2,400 stars, scientists have now created, with unprecedented precision, a three-dimensional map that shows the Milky Way has a twisted shape. [excerpt

Driven Portulum : A Rolling Ball as a Simple Oscillating System

A classroom demonstration, a variation of the simple swinging pendulum, is described. In our portulum, a ball, driven by short blasts of air, rolls along a curved tube. The design of this device, its construction, and its usefulness to the teaching of physics are discussed. It is also shown that the oscillations of the rolling ball have the same mathematical form as the oscillations of the ball swinging along the same path, but with a lower frequency

Optical Photometry and Spectroscopy of the Suspected Cool Algol AV Delphini: Determination of the Physical Properties

We present new spectroscopic and BVRI photometric observations of the double-lined eclipsing binary AV Del ( period = 3:85 days) conducted over six observing seasons. A detailed radial velocity and light-curve analysis of the optical data shows the system to be most likely semidetached, with the less massive and cooler star filling its Roche lobe. The system is probably a member of the rare class of ‘‘cool Algol’’ systems, which are distinguished from the ‘‘classical’’ Algol systems in that the mass-gaining component is also a late-type star rather than a B- or A-type star. By combining the spectroscopic and photometric analyses, we derive accurate absolute masses for the components of M1 = 1.453 + 0.028 M and M2 = 0.705 + 0.014 M and radii of R1 = 2.632 + 0.030 R and R2 = 4.233 + 0.060 R, as well as effective temperatures of 6000 + 200 and 4275 + 150 K for the primary and secondary, respectively. There are no obvious signs of activity (spottedness) in the optical light curve of the binary