Astronomy Colloquium

RR Lyrae stars are once again poised to play a critical role in launching humanity out of the solar system and Milky Way and into the local cosmos. The "era of precision cosmology" has given rise to new tension between the Hubble constant derived from Planck+Standard Cosmology (67) and the local Cepheid-based determination (72), whose difference is larger than the formal errors.  Before inferring "new physics" from this conflict, the Cepheid result must be independently checked.  Several advances in astronomical techniques now permit RR Lyrae stars to play this role.  I report new work toward calibrating RR Lyraes at the 2% level via statistical parallax and argue that they are likely to be exquisite individual distance indicators in the infrared.  Present and future large telescopes should enable precision tests of Cepheid distances to at least a dozen galaxies with a range of properties, the only completely independent test presently imaginable.