Abstract

Over the last couple of decades, the accuracy with which we can measure distances to galaxies and determine Ho has improved significantly. I will discuss two of our most precise methods for measuring distances in the local universe: Cepheids and the Tip of the Red Giant Branch (TRGB). I will present new results from the Carnegie-Chicago Hubble Program (CCHP), the goal of which is to independently measure a value of the Hubble constant to very high precision and accuracy. We have built an entirely new extragalactic distance scale from the ground up. Using the Hubble Space Telescope Advanced Camera for Surveys, the CCHP is using the TRGB to calibrate Type Ia supernovae. Our value of the Hubble constant, Ho = 69.6 / 0.8 (statistical) / 1.7 (systematic) km/sec/Mpc, falls midway between the value obtained from the Planck Cosmic Microwave Background analysis, and that obtained using Cepheids. I will address the uncertainties, discuss the current tension in Ho, and whether there is need for additional physics beyond the standard CDM model.