  Based on the observations of the Chinese Small Telescope ARray (CSTAR), the i
band observing conditions at Antarctic Dome A have been investigated. The over
all variations of sky brightness and transparency are calculated and
subsequently cloud cover, contributions to the sky background from various
factors including aurorae are derived. The median sky brightness of moonless
clear nights is about 20.5 mag arcsec$^{-2}$ in the SDSS i band at the South
Celestial Pole, which contains the diffused Galactic light of about 0.06 mag.
There are no thick clouds in the year of 2008. Relatively strong aurorae are
detected by their brightening the normal sky, which contribute up to about 2 of
the observed images.
