  The expansion of the universe causes spacetime curvature, distinguishing
between distances measured along and transverse to the line of sight. The ratio
of these distances, e.g. the cosmic shear distortion of a sphere defined by
observations of large scale structure as suggested by Alcock & Paczynski,
provides a method for exploring the expansion as a function of redshift. The
theoretical sensitivity to cosmological parameters, including the dark energy
equation of state, is presented. Remarkably, sensitivity to the time variation
of the dark energy equation of state is best achieved by observations at
redshifts z<1. While systematic errors greatly degrade the theoretical
sensitivity, this probe may still offer useful parameter estimation, especially
in complementarity with a distance measure like the Type Ia supernova method
implemented by SNAP. Possible future observations of the Alcock-Paczynski
distortion by the KAOS project on a 8 meter ground based telescope are
considered.
