The Astrophysics Spectator

Issue 2.05, February 2, 2005

Home Commentary Surveys Research Background Previously Site Info
Logo for 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.

February 2, 2005

With this issue of The Astrophysics Spectator, I introduce “live” figures—figures that can be altered by the reader—to this web site. The first live figure shows black-body spectra. The reader can change the temperatures of the spectra, the units of temperature, and the units of photon energy. Along with this figure, I add an index page of live figures under the Background link. The live figures are simpler than the simulators on this web site. I hope that the reader will find the live figures to be more informative than simple gif and jpeg images.

The “Electromagnetic Radiation” path is added to the Surveys page with this issue. The path is a single page on thermal electromagnetic radiation, or black-body radiation. The page discusses how the particle nature of light gives light properties that are similar to a gas, and that, as a consequence, light has the thermodynamic properties of a gas. When light comes into thermal equilibrium with its surroundings, it spectrum and energy density is described by a single temperature. The radiation observed from the Sun and the stars is very close to a thermal radiation field.

In this week's commentary, I discuss the difficulty of seeing the world as we know it to be rather than as our senses portray it.

Jim Brainerd

Current Commentary

Perception. We have a deep understanding of our universe, but can we truly perceive the universe? The scales of our universe are outside of human experience. (continue)

New Background

Thermal Electromagnetic Radiation. The study of the radiation produced by a star must start with a discussion of thermal electromagnetic radiation. The spectrum of a thermal electromagnetic field is called a black-body spectrum, or a Planck spectrum. The black-body spectrum is characterized by a single parameter: a temperature. The electromagnetic spectrum of most stars closely follows the black-body spectrum. This page is the first on the “Electromagnetic Radiation” survey path. This page contains a “live” figure of black-body spectra. (continue)

Live Figure Index. Live figures are figures that can be configured by the reader. The figures are Java applets. They are generally simpler than the simulators on this web site. The index page lists and describes all of the live figures on the web site. (continue)


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