n cosmology, baryon acoustic oscillations (BAO) refers to regular, periodic fluctuations in the density of the visible baryonic matter of the universe. In the same way that supernova experiments provide a "standard candle" for astronomical observations,[1] BAO matter clustering provides a "standard ruler" for length scale in cosmology.[2] The length of this standard ruler (~490 million light years in today's universe[3]) can be measured by looking at the large scale structure of matter using astronomical surveys.[3] BAO measurements help cosmologists understand more about the nature of dark energy (which causes the apparent slight acceleration of the expansion of the universe) by constraining cosmological parameters.