Black Body and Filters

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This is the stub for a lab using the online black body tool and astronomical filters

In PHYS 107 you'll learn that stars glow thermally i.e. across all wavelengths but with different colors depending on their temperature. Astronomy uses filters to measure the colors of stars, essentially colored glass that only lets through a select part of the electromagnetic spectrum.

Getting Started

Open the black body online tool:

Black Bodies and Filters

There is an older version here but it requires Flash.


1. What temperature is the star?

2. What happens if you increase the temperature of this star?

3. The visible spectrum is from 400nm to 700nm. How hot does a star need to be to have it's peak at the blue end?

4. How hot is a star that peaks at the red end of the visible?

5. Can a star peak outside the visible spectrum?

6. Our Sun is yellow. What does that imply for its temperature?

7. At what temperature does Sirius A peak? What wavelength? Can our eyes detect that light?

8. Add a curve (the camera icon, the gray curve stays). What happens when you make that second star hotter than the first?

9. A star that peaks in the blue, does it give off more or less red light than a star that peaks in the red?

10. Compare the Sun and Sirius A. Which appears blue (relative more blue than red light) and which gives off the most light in the red?

11. Add graph values and plot peak wavelength against temperature Plot peak wavelength vs temperature on a graph. What kind or relation is there between these two values?

12. Include 'intensity' on the display. Plot the intensity as a function of temperature f

13. Change the horizontal scale to include up to 6 micron in wavelength. Is there are temperature for a star where it does *not* emit any light at 1-5 micron?

14. Do you think there are stars cooler than the lowest temperature allowed in the slider in this app? Motivate why or why not.

15. Slide one curve to the maximum temperature allowed and fix with the camera icon and one to the lower temperature allowed (a little warmer than Earth). Is there a point in the spectrum that the coolest star shines brighter than the hottest star?