  BOSS, the Baryon Oscillation Spectroscopic Survey, is a 5-year program to
measure the absolute cosmic distance scale and expansion rate with
percent-level precision at redshifts z<0.7 and z~2.5. BOSS uses the "standard
ruler" provided by baryon acoustic oscillations (BAO). BOSS will achieve a near
optimal measurement of the BAO scale at z<0.7, with a redshift survey of 1.5
million luminous galaxies. It will pioneer a new method of BAO measurement at
high redshift, using the LyA forest to 160,000 QSOs in the redshift range
2.1<z<3.0. The forecast measurement precision for angular diameter distance d_A
is 1.0%, 1.0%, and 1.5% at z=0.35, 0.6, and 2.5, respectively, and the forecast
precision for the Hubble parameter H(z) is 1.8%, 1.7%, and 1.2% at the same
redshifts. These measurements will provide powerful constraints on the nature
of dark energy and the curvature of space, complementing the constraints
obtained from other probes. BOSS will also provide a superb data set for
studying large- and small-scale clustering, the evolution of massive galaxies
and the luminosity function and clustering of QSOs at 2.3 < z < 6.5. BOSS is
one of four surveys that comprise SDSS-III (the Sloan Digital Sky Survey III),
a 6-year program that will use highly multiplexed spectrographs on the 2.5-m
Sloan Foundation Telescope to investigate cosmological parameters, the history
and structure of the Milky Way galaxy, and the population of giant planet
systems.
