Definition: In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.
Input: A version of spectroscopy that is free of one form of this effect uses a standing wave to give radiation to a moving atom and is named for its two-photon transition. Due to this effect, atoms observe laser resonance leading to the phenomenon of optical molasses at its namesake cooling limit. Mossbauer spectroscopy uses this effect to modulate the energy of the incident gamma rays. An experiment that used a canal ray tube and a mirror to view light emissions was used to detect the transverse form of this effect, while its relativistic form involves changes equal to the square root of one plus beta over one minus beta. For 10 points, name this shift in the wavelength from a moving source that can be heard by an observer.
Output:
Science