White light zigzagging and hovering over Quebec City

I saw a bright white light moving in the sky in a pattern that I had never seen before. It moved in one direction, then stopped, stayed immobile for a few seconds, then started to move in another direction, and stopped again.  It repeated that sequence many times.  There were no sound.
I was sitting on the balcony of my apartment, having dinner before going back to work.  The sky was clear, i.e., no clouds, and it was daylight.   This was not a satellite, a helicopter, an airplane, a meteorite or northern lights.  I have seen many of those and the behavior of that light was nothing like it.  This was not Venus or Jupiter.  It was as bright as Venus, but was moving rapidly instead of the slow motion that a planet would display.  
I am a scientist with a B. Sc. in physics and a Ph.D. in molecular biology.  I have worked in a planetarium and I am quite familiar with objects in the sky.
Witness indicates that date of the sighting is approximate.  PD