We began our learning day with another CLEA lab, "Classification of Stellar Spectra." The idea behind this lab was to be use what we know (data) to classify what we don't know. We used known spectra of main sequence stars and compared them the spectra of unknown stars. I found the mnemonic 'Oh BE A Fine Girl, Kiss Me,' (OBAFGKM) to be very helpful in identifying the age and temperature of stars. The order goes from hot to cold, young to old. We determined the elements of the star by using absorption lines for further refinement of the classification. We also learned that it is possible to use the spectra of the star to identify it. I understood much of the concept of what we were doing but the actual doing was another story!
Following a short break Caroline gave a lecture, "Stellar Spectra in the Classroom." I have so many notes from this lecture! Spectroscopy breaks light into different wavelengths (different colors). These make up the visible spectrum of colors, red, orange, yellow, green, blue, indigo, violet (roygbiv). She spoke about where visible light fits in the electromagnetic spectrum, the progression of long wavelengths (radiowaves) to short (gamma rays) and the effect of those waves on humans. Caroline gave us a historical background beginning with the contributions of Joseph Frauenhofer, Annie Jump Cannon, and Cecilia Payne. It was nice to get this human element in the midst of so much factual information!
Caroline then gave a description of fusion and fission that will help me keep them straight. She told us fusion, which takes place in stars, takes parts and makes a whole. Specifically she said nature puts together, humans take apart.
Spectral lines form in the photosphere, an outer, cooler layer of the star. She then led us through continuum (continuous), emission (forms bright lines) and absorption (forms dark lines) spectra. Finally Caroline talked about rainbows which reflect and refract light. She also explained why the colors are always in the same order. Something I need to review on my own!
The lecture then went on to reinforce the material from the morning lab. The appearance of the spectra of a star is dependent on the temperature of the star:
Classes OBAFGKM; Color progression blue-->red; temperature progression hot-->cold.
How can you tell if a star is moving? By it's shift! A redshift star would emit a longer wavelength and would be moving away. A blue/violetshift star would be moving closer.
Wow! What a morning! Thank goodness for lunch and a chance to decompress!
In the afternoon we made spectroscopes and used them to color the patterns and identify the emission patterns we found in the spectra of a regular light bulb, flourescent light, argon, and helium. NDeRC gave us several spectrometers to take back to our classrooms.
For the final activity of the day we used Oreo cookies to model moon phases by opening the cookies and scraping off the frosting. We then put the cookies in correct postion in relation to the Earth and Sun. Remember, waxing on, waning off! This is a fun elementary lab available online.
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