Instructions - Blackbody Spectrum Viewer

Blackbody Viewer - Spectral Representations

Purpose:The blackbody calculator allows for visualization of the spectrum produced by objects of a given temperature.

General Information:

1. Use the slider bar to change the temperature in Kelvins.
2. The left view shows the spectrum of log intensity vs. log wavelength.
3. The middle view shows what we would see if we split the light using a prism.
4. The right view shows the apparent color of the object with all colors of light mixed together.

Alternate version:

1. The right view shows how a star with the given temperature, radius, and distance from the Earth will appear through a standard telescope.
2. Notice that for many changes of distance and size, while the star may brighten or dim, it will not appear to change in size. This is because the stars in the night sky are so far away from us that we cannot make out anything but a spot of light.
3. For stars that become very bright, when we try to look at them through a telescope our eyes, or the cameras that the telescopes are attached to, will become saturated. This is similar to film that is over exposed. Our ability to perceive details in color diminishes. Objects appear larger, as a halo seems to form around the object. When looking through a lens such as that found in a telescope or in the human eye, diffraction spike will appear creating a 4 pointed cross centered on the image.

Blackbody Viewer - Data Fitting

Purpose:The blackbody fitting tool allows for comparisons of a model of blackbody radiation to actual astronomical data.

General Information:

1. The graph on the upper left shows a model of blackbody radiation compared to astronomical data in the given passbands.
2. The data entry panel on the upper right allows you to enter in astronomical data in the given passbands.
3. The control panel on the bottom left allows you to modify the temperature, size, and distance to the model star. You can use either the slider bars or the text entry boxes to enter model parameters.
4. The goodness of fit panel on the bottom right shows a few typical indicators of fit quality. Often you are given the magnitude difference in the B and V passbands (sometimes called B-V or color index), so the B-V value for the model is displayed. If you have entered in your data in B and V, then the difference between the model's B-V value and your data's B-V value is displayed for you. This is often a good way of determining if your temperature in your model is correct, as it does not depend on the total magnitude (height of the curve), just the relative magnitude between B and V (shape of the curve). Once you have gotten the temperature to fit, if you know the size of the star, you can use the chi-squared value for the overall fit to get the distance to the star. If you know the distance, you can get the size. But you cannot determine one with this method without knowing the other first.