  We made optical observations of the Gegenschein using a
liquid-nitrogen-cooled wide-field camera, Wide-field Imager of Zodiacal light
with ARray Detector (WIZARD), between March 2003 and November 2006. We found a
narrow brightness enhancement superimposed on the smooth gradient of the
Gegenschein at the exact position of the antisolar point. Whereas the
Gegenschein morphology changed according to the orbital motion of the Earth,
the maximum brightness coincided with the antisolar direction throughout the
year. We compared the observed morphology of the Gegenschein with those of
models in which the spatial density of the interplanetary dust cloud was
considered and found that the volume scattering phase function had a narrow
backscattering enhancement. The morphology was reproducible with a spatial
distribution model for infrared zodiacal emission. It is likely that the
zero-phase peak (the so-called opposition effect) was caused by coherent
backscattering and/or shadow-hiding effects on the rough surfaces of individual
dust particles. These results suggest that big particles are responsible for
both zodiacal light and zodiacal emission. Finally, we derived the geometric
albedo of the smooth component of interplanetary dust, assuming big particles,
and obtained a geometric albedo of 0.06+-0.01. The derived albedo is in
accordance with collected dark micrometeorites and observed cometary dust
particles. We concluded that chondritic particles are dominant near Earth
space, supporting the recent theoretical study by dynamical simulation.
