Variations of the Interstellar Extinction Law within the Nearest
  Kiloparsec
  Multicolor photometry from the Tycho-2 and 2MASS catalogues for 11 990 OB and
30 671 K-type red giant branch stars is used to detect systematic large-scale
variations of the interstellar extinction law within the nearest kiloparsec.
The characteristic of the extinction law, the total-to-selective extinction
ratio $R_V$, which also characterizes the size and other properties of
interstellar dust grains, has been calculated for various regions of space by
the extinction law extrapolation method. The results for the two classes of
stars agree: the standard deviation of the "red giants minus OB" $R_V$
differences within 500 pc of the Sun is 0.2. The detected $R_V$ variations
between 2.2 and 4.4 not only manifest themselves in individual clouds but also
span the entire space near the Sun, following Galactic structures. In the Local
Bubble within about 100 pc of the Sun, $R_V$ has a minimum. In the inner part
of the Gould Belt and at high Galactic latitudes, at a distance of about 150 pc
from the Sun, $R_V$ reaches a maximum and then decreases to its minimum in the
outer part of the Belt and other directions at a distance of about 500 pc from
the Sun, returning to its mean values far from the Sun. The detected maximum of
$R_V$ at high Galactic latitudes is important when allowance is made for the
interstellar extinction toward extragalactic objects. In addition, a monotonic
increase in $R_V$ by 0.3 per kpc toward the Galactic center has been found near
the Galactic equator. It is consistent with the result obtained by Zasowski et
al. (2009) for much of the Galaxy. Ignoring the $R_V$ variations and
traditionally using a single value for the entire space must lead to systematic
errors in the calculated distances reaching 10\%.
