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.

Different versions of this phenomenon have been experimentally tested by Ives and Stilwell on hydrogen atoms in 1938. Cherenkov radiation and verification of the absence of a medium of transmission for light are important consequences of its relativistic formulation. Johannes Stark predicted that high velocity rays of positive ions will demonstrate it, while Buys-Ballot [BOYS-ba-LOH] first verified it in 1845. First described by an Austrian scientist in 1842, FTP, name this effect that explains why a moving observer perceives a wavelength different from the source wavelength.
Science