The Astrophysics Spectator

The basic layout of the site is as survey paths, which can be found under the Surveys link at the top of this and most other pages on this site. Each survey begins with a basic overview of the subject. Part of this overview include simulators of astrophysical phenomena that allow the reader to experiment with the phenomena. The later pages in a survey present the subject in greater and more mathematical depth. A path ends with research pages that describe current research projects and results in astrophysics.

The links at the top of each page are Home, which is the current home page of this site, Commentary, which is an index of short essays on topics loosely related to astrophysics, Surveys, which is the index of survey paths, Research, which is the index of research pages and the page leading to recent news items, Background, which is the index page for all background information on astrophysics, including survey pages, simulator pages, tables, bibliographic references, and lists of web resources, Previously, which is an index of previous home pages, and Site Info, which describes the site and its author, and gives contact information.

Each Wednesday, a new issue of The Astrophysics Spectator is published that comprises a new home page, a new commentary, whatever news the author notices, and background, research, and simulator pages added to the survey paths. The home page acts as an index to the newly added pages. This site also has an RSS channel, whose link is given at the bottom of the right-hand column of this page.

January 26, 2005

We return to the stars in this week's edition of The Astrophysics Spectator. We add three pages to the “Stars” survey path. The topics of these new pages are the general internal structure of stars, the transport of energy through a star by electromagnetic radiation, and the transport of energy by convection.

In this week's commentary I note the similarity of the geological processes seen on Titan to those on Earth, and remark that this is another reminder of how our complex universe reduces to a handful of simple processes.

This week I add a page of links to external sites. This page serves two purposes: it is a place to note interesting and useful resources on the web, and it is a means of reciprocating links from other sites to this site.

You may notice some changes to the home page with this issue. I have removed the News link at the top of the page, and in its stead I have added a Survey link that points to the index page for the survey paths. The survey paths have become a central component of this web site, while the news page has become something of an afterthought. News items will still be added from time to time, and they will be noted on the home page. The News page is now linked to the Research page. I have also removed the link table to subsections of the home page, as the home page is short, and the link table unnecessarily cluttered it. Finally, I have added a masthead to the left of the home page that describes the web site and the major links at the top of each page.

Current News

First Scientific Results from the Huygens Landing on Titan (January 21, 2005). The Huygens science team has released the first results from the January 14, 2005 landing of the Huygens probe onto Titan. The team stated that the Titan terrain bears the marks of the precipitation and flow of liquid methane. The surface of Titan was found to be a loose soil of water-ice particles mixed with water-ice pebbles. (continue)

Current Commentary

Titan and Earth. The high-altitude photographs of the Huygens probe of Titan's surface bring to mind aerial pictures of the high desert of the United States. Despite having a temperature closer to absolute zero than to Earth's temperate temperatures, Titan is shaped by some of the processes that shape Earth. Titan is another example of how simple our universe is, and it is an example of how unusual Earth is. (continue)

New Background

Structure of a Stellar Interior. Stars have a very simple internal structure. This page describes the general structure and basic physics found in all non-degenerate stars. (continue)

Radiative Transport in a Star. The energy released by a star's gravitational contraction and thermonuclear burning of hydrogen, helium, and other elements is converted into electromagnetic energy. The diffusion of this radiation is one of the two energy transport mechanisms a star employs to dump energy at the surface, where it is radiated into space. The effectiveness of radiative transport depends on the state of the plasma in the star and on the rate at which the temperature drops with distance from the star's center. (continue)

Convection in a Star. Stars usually have a region in their interior that is convective. Convection happens when the temperature drops too rapidly through the star. When a layer becomes convectively unstable, energy is carried through this layer by convection rather than by radiative transport. Convection ensures that a layer is continually mixed, so that the layer's elemental composition is uniform. (continue)

Resources in Astrophysics. This page is an index of links to other web sites that present astronomy and astrophysics. The links are listed because the author has found them to be interesting and useful. Some links are to sites that link back to this web site. (continue)