Part A - Using spectroscopy to determine star movement and distance from Earth Spectroscopy is one means of studying stellar behavior. After dispersing white light (or any part of the electromagnetic spectrum) into a broader spectrum, we can investigate whether objects are emitting or absorbing specific, characteristic wavelengths. In this way, we can investigate the composition of objects far away. However, the Doppler effect may impact the characteristic wavelength. The Doppler effect causes wavelengths emitted by a source to shorten or lengthen based on the movement of the source with respect to the observer; see the ambulances figure below. Note how the ambulance-sourced sound waves change as it approaches and moves away from the observer. If the source (the ambulance below) is moving toward the observer, then the source is getting closer to the wavelengths as they are emitted, shortening them. If the source is moving away from the observer, the wavelength is longer because the source is moving away from the waves as it emits them, stretching the wavelength. In summary, the Doppler effect gives us information about the relative motion of objects in addition to the information that would be collected using spectroscopy, but not absolute distance between them. Figure A depicts the Doppler effect as it affects an ambulance approaching an observer. Figure B depicts the Doppler effect as it affects an ambulance moving away from an observer. The distance between the ambula

This star is also moving toward Earth, but it is not the fastest. This star is moving the fastest toward Earth. This star is moving neither toward nor away from Earth. This star is moving away from Earth. This star is the closest to Earth. This star is the farthest from Earth. Label for direction traveling to/from Earth STAR Wavelength of Absorption Line A 649 nm B 656 nm 658 nm 647 nm