About SPEX
Adding Spectra
Data Files
Emission line
Graphing Options
Wavelength/Frequency Range
Color band options

Spectrum Explorer

User's Guide


About SPEX  top

The Spectrum Explorer (SPEX) is a powerful new tool which allows users to simultaneously plot and compare multiple spectra, including blackbody spectra of any temperature, astronomical data files, and hand-drawn plots. This Java applet is designed to help students explore and understand spectral properties of light such as blackbody radiation (including the Stefan-Boltzmann and Wien peak), Kirchhoff’s Laws, and the nature and sources of emission and absorption line spectra.

The Spectrum Explorer was developed as part of Project LITE (Light Inquiry Through Experiments), an ongoing software, curriculum, and materials development project within the Boston University Science and Mathematics Education Center. The educational goal of this project is to help students gain insight into the nature of light and spectra through individualized hands-on, eyes-on, and minds-on learning. Other components include unique take-home laboratory materials and experiments, written curriculum guides, lecture demonstrations, and web-based visual effects and illusions. These can all be found at

Running/Installing SPEX  top

Running the applet online:

The Spectrum Explorer uses the Java Plug-in to run as a Swing based applet within your web browser.


SPEX will run on a Macintosh only in MacOS X. It will not run on MacOS 9.x or earlier. The applet will run on all internet browsers that are supported by MacOS X, including Internet Explorer 5.2 and Netscape 6.0.


The SPEX applet will run on a PC under Windows 2000 and XP with Netscape 7.0 and Internet Explorer.

Installing the Spectrum Explorer for off-line use:

The installer installs the spectrum explorer on your computer so that you can run it offline as an application. It works on all PC platforms and MacOS X. It does not run on MacOS 9.x or earlier.

Adding Spectra  top

Blackbody Spectra  top

Using the Spectrum Explorer, you can plot a blackbody spectrum for any temperature. To add a blackbody, click on the Add pull-down menu at the top left of the SPEX window and select blackbody or click on the Blackbody shortcut button at the bottom of the window. From the menu, you will have the option of plotting the blackbody spectrum as a function of wavelength (w) or frequency (f). If you add a blackbody using the shortcut button, the spectrum will automatically be plotted as a function of wavelength (w). Once you have added a blackbody spectrum, a thermometer graphic will appear on the right hand side of the window. The default temperature is set to 5700 K (the approximate temperature of the Sun). You may adjust the temperature of the blackbody either by using your mouse to click and drag the mercury in the thermometer or by entering the desired temperature in the text box below the thermometer and hitting “Enter” on your keyboard.

Quantitative information about each blackbody spectrum is displayed just above the corresponding colorband for that spectrum. This information includes the temperature of the blackbody, the location of the Wien peak, the Stefan-Boltzmann flux, and the percentage of radiation emitted in the infrared (IR), visible, and ultraviolet (UV) portions of the electromagnetic spectrum. On either side of the colorband is a color patch which shows the overall “color” of the spectrum.

A black box surrounding the colorband and color patch indicates when a spectrum is selected or “active.” By default, the last spectrum added will be active unless you select another spectrum. To do so, click on the colorband for that spectrum. To remove any spectrum, first ensure that the spectrum is activated. Then either choose “Remove Selected Spectrum” from the “Add” pull-down menu or click on the “Remove” button at the bottom of the SPEX window.

If at any time you would like to see the data for any spectrum, you may do so by activating that spectrum and choosing “Show Spectrum Data” from the “Add” menu. This will bring up a table of x- and y- data values for the selected spectrum.

Data Files  top

            The current version of the Spectrum Explorer contains about 30 astronomical data files, mainly stellar and galactic spectra.  To display one of these data files, choose “Data File” from the “Add” pull-down menu at the top of the SPEX window or click on the “Data File” button at the bottom of the window.  A dialog box will pop up, allowing you to choose the file you wish to plot.

Emission Line Spectra  top

            The Spectrum Explorer allows you to view characteristic emission line spectra of any element on the periodic table.  Either choose “Element” from the “Add” pull-down menu or click on the “Element” short-cut button to bring up the periodic table of elements.  Click on whichever element you wish to display.  Once you have chosen an element, you will be given the option to choose to display any single ionization state or all ionization states simultaneously.  The database currently contains allowed transitions only.  Forbidden lines will be added in the near future.

Drawing  top

To draw your own editable spectrum, choose “Drawing” from the “Add” pull-down menu or click on the “Drawing” button at the bottom of the window to activate the drawing tool.  To create your own spectrum on the plot area, click and drag your mouse across the grid.  This spectrum is editable at any time provided the spectrum is highlighted.

Astronomy  top

            Choosing “Astronomy” from the “Add” menu or clicking on the “Astronomy” button allows you to view astronomical images and spectra simultaneously.  This section currently contains only a handful of galaxies of various Hubble types and the Crab Nebula supernova remnant.  To view galaxy spectra, choose the “Hubble Tuning Fork” option and click on the thumbnail image of the galaxy whose spectrum you wish to display.  To view spectra of various regions of the Crab Nebula, select the “Crab Nebula” option.  Active regions of the image are surrounded by red boxes.  Clicking your mouse in any of these designated areas will display the spectrum of that particular region.  Use the tabs at the top of the Crab image to toggle between views of the entire nebula and magnification of the central region.

Tools  top

Measure  top

Ø    Mouse Coordinates  top

            To display the x- and y-coordinates of the position of your mouse at any time, choose the “Measure … -> Mouse Coordinates” from the “Tool” pull-down menu at the top of the SPEX window.  Coordinates will be displayed above the top left corner of the plot grid.


Ø    Spectrum Coordinates  top

By choosing “Measure … -> Spectrum Coordinates” from the “Tools” menu, you can activate a measuring tool that traces the curve of the active spectrum and displays the x- and y-coordinates of the spectrum.  As with the “Mouse Coordinates” measuring tool, the “Spectrum Coordinates” tool will display x- and y- values above the upper left corner of the plotting area. 


Ø    Turning Off Measuring Tools  top

Once you have activated one of the measuring tools, that tool will remain active until you turn it off.  To do so, select “Measure Off” from the “Tools” menu.

Normalize  top

Spectra may be displayed on either a normalized (0 to 1) or absolute scale.  Either of these options can be selected through the “Normalize” choice within the “Tools” menu.  When exploring properties of a blackbody spectrum such as the Wien peak, it is best to choose normalized coordinates.  An absolute scale is better suited to exploring properties such as the Stefan-Boltzmann Law.

When comparing two spectra such as a blackbody spectrum and a stellar data file, you may wish to adjust the height of one of the curves to achieve a better fit.  To do this, select the spectrum you wish to adjust and choose “Click and drag to adjust” from the “Normalize” option within the “Tools” pull-down menu.

Graphing Options  top

Graphical Display

Ø    Coordinate System

Spectra are displayed as both a color band and an Intensity vs. wavelength or frequency plot.  By default, spectra will be displayed graphically as Intensity vs. wavelength.  Use the “Coordinate System” pull-down menu to switch to Intensity vs. frequency.

Ø    Wavelength/Frequency Range

Depending on the coordinate system you have chosen, either the “Wavelength Range” or “Frequency Range” pull-down menu will be active.  From these menus, you can select the range of wavelengths or frequencies over which you wish to plot.

Colorband Display

The “Colorband” pull-down menu gives you three options.  You may choose to view the colorband either in color or black and white.  If you are using the Spectrum Explorer to look at emission line spectra, you may also choose the “Enhance Line Spectra” option, which boosts the intensity of emission lines shown on the colorband in order to enhance the visibility of weaker lines.