How to Detect the Red Shift & Blue Shift of a Star
The terms "red shift" and "blue shift" refer to changes in the wavelength of observable light waves being emitted from objects in the universe moving in relation to the observer. These changes are attributable to the "Doppler Effect," wherein the observed wavelength of light (or sound) waves increase as the emitting objects move away from the observer, or decrease as the emitters move closer. Red shifting occurs when the electromagnetic (light) wavelengths seem longer and therefore closer to the wavelengths of what humans perceive to be the color red. Blue shifting is the opposite, where the waves are shortened and thus consequently closer to the color humans see as blue.
Accounting for red shifting or blue shifting is crucial to astronomical knowledge of stars and the universe as a whole, because astronomers draw conclusions about those and many other celestial bodies by observing the light emitted from those stars through their absorption spectra that. Every star has a unique light signature based on the makeup of gases on their surfaces, but to properly understand a star's composition, we must account for the ways that red or blue shifting alter our observations of their light.
The first spectroscope was a simple prism that required painstaking graphing and comparison of the spectra to established data. Today, however, you can make a powerful, easy-to-use spectroscope to quickly analyze a star's light and detect the Doppler effect shifting.
Things You'll Need
List of laboratory standards for elements' wavelength emissions
Computer
Diffraction grating filter lens (also known as "star analyzers")
Web camera
Spectrum analysis software
Telescope (for more distant stars)
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Instructions
Taking the Star's Absorption Spectrum to Find the Doppler Shift
1
Making and using a modern day spectroscope is much easier than in the old days!
Attach the diffraction grating lens to the web camera; a camera plus a diffraction lens together are considered a "spectroscope." Hook your newly fashioned spectroscope up to your computer.
2
Point the spectroscope at your star of choice and snap a photo. If the star is sufficiently far away (and thus harder to see), you may need to hook up your spectroscopic camera to a telescope.
3
Load the spectroscopy analysis software on your computer and input your spectrum image to determine which wavelengths the absorption lines for various elements are. Hydrogen, ionized calcium, magnesium and sodium lines will probably be the main absorption lines.
4
Periodic Table of Elements
Take the absorption line measurements and pair them to your list of established laboratory standards for each element's absorption line.
5
Divide the observed wavelength of an element's absorption lines that you found with your spectroscope by the laboratory standard wavelength. The fraction of your observed wavelength over the lab standard will be almost identical for any element you pick, but if you find them to be slightly different, average the fractions of each element's absorption lines to improve your accuracy.
6
Subtract 1 from your fraction; the result is your red or blue shift value. If its value is positive, then it is a red shift (the star is moving away from you), and if it is negative, it is a blue shift (the start is moving toward you).
