Bright, irregular, flashes across the night sky similar to alien Iridium flare.

The object started near west (~260 deg) and continued to east alternating between very bright flashes and dim flashes over different intervals.  It crossed near the rate of a plane but very direct.  It was dusk with just a bit of light blue on the horizon and the stars of the Big Dipper were just becoming visible.  The brightness for a brief flash was as bright as the surface of the moon and was consistently brighter than Venus.  I checked HA ((www.Heavens-Above.com)), and nothing matched the discription.
We have amended the time above, in order to reflect a nighttime sighting.  We spoke via telephone with the witness, and he seemed to us to be serious-minded.  We suspect that he is a very good witness.  PD