  The Sloan Digital Sky Survey (SDSS) surveyed 14,555 square degrees, and
delivered over a trillion pixels of imaging data. We present a study of galaxy
clustering using 900,000 luminous galaxies with photometric redshifts, spanning
between $z=0.45$ and $z=0.65$, constructed from the SDSS using methods
described in Ross et al. (2011). This data-set spans 11,000 square degrees and
probes a volume of $3h^{-3} \rm{Gpc}^3$, making it the largest volume ever used
for galaxy clustering measurements. We present a novel treatment of the
observational systematics and its applications to the clustering signals from
the data set. In this paper, we measure the angular clustering using an optimal
quadratic estimator at 4 redshift slices with an accuracy of ~15% with bin size
of delta_l = 10 on scales of the Baryon Acoustic Oscillations (BAO) (at
l~40-400). We derive cosmological constraints using the full-shape of the
power-spectra. For a flat Lambda CDM model, when combined with Cosmic Microwave
Background Wilkinson Microwave Anisotropy Probe 7 (WMAP7) and H_0 constraints
from 600 Cepheids observed by HST, we find \Omega_\Lambda = 0.73 +/- 0.019 and
H_0 to be 70.5 +/- 1.6 km/s/Mpc. For an open Lambda CDM model, when combined
with WMAP7 + HST, we find $\Omega_K = 0.0035 +/- 0.0054, improved over
WMAP7+HST alone by 40%. For a wCDM model, when combined with WMAP7+HST+SN, we
find w = -1.071 +/- 0.078, and H_0 to be 71.3 +/- 1.7 km/s/Mpc, which is
competitive with the latest large scale structure constraints from large
spectroscopic surveys such as SDSS Data Release 7 (DR7) (Reid et al. 2010,
Percival et al. 2010, Montesano et al. 2011) and WiggleZ (Blake et al. 2011).
The SDSS-III Data Release 8 (SDSS-III DR8) Angular Clustering Data allows a
wide range of investigations into the cosmological model, cosmic expansion (via
BAO), Gaussianity of initial conditions and neutrino masses. (abridged)
