"An Era of Precision Astrophysics: Connecting Stars, Galaxies and the
  Universe," an Astro2010 Science White Paper
  Abridged: The golden age of astrophysics is upon us with both grand
discoveries (extra-solar planets, dark matter, dark energy) and precision
cosmology. Fundamental understanding of the working of stars and galaxies is
within reach, thanks to newly available precision measurements. We highlight
the importance of distances and model independent distances and masses.
  Distances are fundamental in astrophysics and their knowledge can change our
perception of phenomena dramatically: e.g., in antiquity, the Heliocentric
model was rejected because the predicted stellar parallaxes were not observed.
  Distance measurements are directly related to the history & fate of the uni-
verse as they provide 2 of 3 methods available to date the universe. The 1st
method is based on the ages of stars, which can be ascertained if their lumi-
nosities (distances) are accurately known. The 2nd method relies on cosmolo-
gical methods. To 1st order, the age of the universe is the inverse H_0.
  As stressed by the previous decadal report, "the fundamental goal of ...
astrophysics is to understand how the universe ... galaxies [and] stars ...
formed, how they evolved, and what their destiny will be." These questions can
be answered partly by micro-arcsecond astrometry: 1) Galactic archeology: a
detailed reconstruction of the formation history of the Milky Way and other
Local Group galaxies, 2) the very oldest stars in the Milky Way and the age of
the Universe, and 3) H_0 and concordance cosmology.
  These goals are achievable by combining muas-arcsecond astrometry from the
proposed SIM-Lite mission supplemented with ground-based spectroscopy. The
results of our proposed project will force the biggest reassessment of stellar
astrophysics in 50 years, which will affect most branches of astrophysics.
