Lab 10: Spectroscopy
Please summarize the important concepts of this lab.
- What information can you learn about a celestial object just by measuring the peak of its blackbody spectrum?
- What does a blackbody spectrum look like?
- How does the peak wavelength change as the temperature of a blackbody changes?
- How can you quantitatively measure the color of an object?
- Do the color of items you can see around you on Earth tell you something about the temperature of the object? Why or why not?
- What information can you learn about an astronomical object from its spectrum?
- Explain how you would get this information from a spectrum.
Extra Credit
The program is located here .
The program just produces a graph of wavelength on the x-axis vs. brightness on the y-axis; you are looking at the relative brightness of this source at different wavelengths.
The program is simple to use. There is a sliding bar on the bottom of the applet that allows you to set the temperature of the star. Play around with it a bit to get the idea. Be aware that the ya-xis sacle of hte plot will change to make sure that none of the spectrum goes off the top of the plot; thus if you are looiking at objects of different temperatures, the y-scale can be different.
Note that the temperature of the objects are measrued in units called degrees Kelvin. This are very similar to degrees centigrae, the only difference is that K = C+ 273. So if the outdoor temperature is 20C, then it is 293K. Temperatures of stars are mreasured in the thousands of degrees Kevlin; they are much hotter than it is on Earth!
1. Set the object to a temperature of 6000 degrees, which is the temperature of the Sun. Note the wavelength, and the color of the spectrum at the peak of the blackbody curve.
2. Now set the temperature to 3000K, much coolor than the Sun. How do the spectra differ? Consider both the relative amount of light at different wavelengths as well ast he overall brightness. Now set the temperature to 12,000 K, hotter than the Sun. How do the spectra differ?
3. You can see that each blackbody spectrum has a wavelength where the emission is the brightest (the top of the curve). Note that this wavelength changes as the temperature is changed. Make a table for the peak of the curve for objects at 3000, 6000, 12000, and 24,000 K. Record the peak wavelength for each of these temperatures. You can read the wavelengths by looking at the x-axis value of the peak.
4. Can you see a pattern from your table? For example, consider how the peak wavelength changes as the temperature increases by a factor of 2, a factor of 3, .... Can you come upw ith a mathematical expression which relates the peak wavelength to the temperature? (try plotting the data and fitting a line to it).
5. Where do you think the peak wavelength would be for objects on the Earth, at a temperature of 300K?