Résumé :
Powerful water maser emission (water mega-masers) can be
found in accretion disks in the nuclei of some galaxies. Besides
providing a measure of the mass at the nucleus, such mega-masers can be
used to determine the angular diameter distance to the host galaxy,
based on a simple model. We will explain the importance of determining
the Hubble Constant to a high accuracy for constraining the equation of
state of Dark Energy and present recent results of the Mega-maser
Cosmology Project that has the goal of determining the Hubble Constant
to ~3\%. In addition, we will also present a brief status report of NRAO
facilities and some key science projects.
