The Dynamic Cosmos

Beta Version 1.0

A collection of interactive applets for Astronomy

This project was funded by a grant from the National Science Foundation. This CDROM contains only a portion of material that is being released as a somewhat complete package. On this CDROM you will find 9 applets together with some html based tutorials, limited documentation on applet functionality and parameter tags, and some suggested activities.

This software is Beta with a capital B. We fully expect lots of problems. Although we have extensively tested it internally we still expect problems Please report them to

All of the applets on this CDROM are written in the new JAVA 2 API which browsers do not yet handle. Hence, there are two versions of this applet. The version labeled _plugin.html makes use of a plugin that is available for Netscape or IE that will handle these applets.

However, we recommend that the applets be run in the appletviewer environment on a PC. This kit can be downloaded from SUN . Alternatively, the beta release of Netscape 6 also handles JAVA 2 directly. We have put the appletviewer environment on this beta version of the CDROM and it should work if you want to run off the CDROM directly. Performance of these applets will depend quite a bit on machine speed and graphics capabilities.

If you run from a browser the applet will open up in separate window so that the instructions, etc are visible on the main browser page. Should be running these applets from appletviewer (e.g. in a dos shell you would type appletviewer parallax.html ) then the applet will run there so just close the applet pop-up box that the html page triggers (likely no applet would have appeared there anyway).

Although these applets can be run directly from the CD, we recommend you just dump the contents of the CD onto a folder on your hard drive and run from there. All the links are relative so there should be no problem here.

A brief description of these applets can be found below. Updates of this description as well as links to any modified applets will be located at Expanded documentation and student exercises, when they get written, will appear there as well.

The applets contained on this CDROM are the following:

0. Spectral Lines of Elements: This bring up a periodic table. The user can click on an element and its spectrum will appear. Wavelengths of the lines can be measured with a cursor. A useful start for understanding stellar spectra.

1. Blackbody: This is a quite useful applet that lets the user learn Wien's law, measure color indices through the correct filter bandpasses as a function of blackbody temperature and, in a more advanced application, allows the user to draw from a library of stars and fit them to a blackbody temperature and to then do synthetic photometry on the stellar spectra. A secondary applet deals with E aT4 by allowing the user to compare two blackbodies of different temperatures and counting the number of grids under their curves (e.g. measuring the area).

2. Atomic Emission: This is a simple, possibly useless, applet that lets the user move a virtual electron to an energy level. The electron then cascades down, according to defined transition probabilities, and a photon of indicated wavelength is emitted. A side panel shows a view of this transition in the "orbital" model of the atom.

3. Atomic Absorption: This is a robust applet that may be compromised if run on slower machines. The user selects a stellar temperature and a stream of photons is then emitted. The proportion of red, green and blue photons are controlled by the temperature and the stellar continuum is built up on the detector. There is also a schematic photon counter which has enough wavelength coverage that you will see the shape of the black body (at least in the optical region). Once a continuum is built up the use can select a cool gas (currently only hydrogen is available) and wait for absorption lines to appear on the detector which shows the continuous spectrum. Cursor mouseovers will bring up a little box which shows the wavelength and the relative number of counts in the line. That way a student could measure the ratio of Ha to Hb, for instance.

The behavior of this applet is controlled strictly by the Boltzmann factor (exp -(kt/hv)). As a result, a 10000 degree blackbody will produce the Balmer series, but a 7500 degree one barely will, and a 5000 degree one never will.

As there is later an applet that lets the user measure equivalent widths as a function of spectral type, doing this applet first should prepare them to realize that Hydrogen lines are not produced in all stars and that temperature is a controlling parameter.

4. Recombination: This represents the case of an ionized gas cloud (Hydrogen) and the generation of a recombination spectrum. There is rather little interactivity associated with this applet and its intent is to get the students to try and understand the form and relative line strenghts in the hyrogen recombination spectrum. They can also determine temperature of stars that are required for ionization of hydrogen as the boltzmann factor is in this applet as well.

5. Equivalent Width: This applet loads in David Silva's library of stellar spectra or Rob Kennicutt's integrated spectra of galaxies into a tool which allows the user to measure line location, line strengths, directly compare spectra, etc. This has been field tested on may students with positive results. Its fairly straightforward to use and should run fine on all platforms.

6. Parallax Machine This applet uses the Third Catalog of Nearby Stars as its database. There are approximately 3000 parallax measurements in this catalog. A large range of parameter tags is available to select different cuts through this catalog. Stars are loaded into a viewer and are coded by their color. Dot size is proportional to their magnitude. The user selects a star and a measuring window opens from which the parallax can be measured. The parallax measurement includes random errors. The number of measurements that can be made on a single star can be fixed or can be infinite (but you would have to wait a long time). When the user determines the parallax they enter that value and the luminosity is calculated. Hitting the plot star button places that star on the HR diagram. So, this applet is a mechanism for students to construct the HR diagram from the available trig. parallax sample, complete with parallax errors built into it.

7. Inverse Square Law This is an improvement and modification of one of our older applets. In this case there is a star on a detector and the detector has noise. Students can measure either a flux (photons per sq cm per sec) or a magnitude as a function of distance. The noise and brightness of the test star are controlled by parameter tags. One can set up many situations here, such as measuring the same brightness star on detectors with different noise levels, showing that if you are closer to the star, at a give noise level, your measurements will be of higher signal-to-noise, etc. The point is for the students to learn about a) noise, b) signal-to-noise and c) detection in this one applet.

8. CCD Detector Simulator This is a brand new applet that is simple in design and is meant to emphasize one point - that detectors have noise and that detection of an object requires a minimum signal to noise. This simulator is meant as a precursor to the actual measurement using the applet below.

9. FITS Image Handler and much more: This is a very robust applet and is a real complete package. It is designed to be the JAVA version of the IRAF Ximtool but with builtin photometric capability. As part of this applet, we distribute FITS data for specific exercises that was taken with our new CCD system at the Pine Mountain Observatory . Semi-complete documentation for this tool is available in the html links below:

Test Drive the Applets