Grey Milky Way Extinction from SDSS Stellar Photometry
  We report results concerning the distribution and properties of galactic
extinction at high galactic latitudes derived from stellar statistics using the
Sloan Digital Sky Survey (SDSS). We use the classical Wolf diagram method to
identify regions with extinction, and derive the extinction and the extinction
law of the dust using all five SDSS spectral bands. We estimate the distance to
the extinguishing medium using simple assumptions about the stellar populations
in the line of sight.
  We report the identification of three extinguishing clouds, each a few tens
of pc wide, producing 0.2-0.4 mag of g'-band extinction, located 1-2 kpc away
or 0.5-1 kpc above the galactic plane. All clouds exhibit grey extinction,
i.e., almost wavelength-independent in the limited spectral range of the SDSS.
We discuss the implication of this finding on general astrophysical questions.
