'Iridium' is the name for a series of communication sattelites. These satellites have large, flat antennae that reflect sunlight in a narrow path as they orbit. If you're in the path, you'll see it as a very brilliant object that moves and fades away in a few seconds. Magnitude -8 is brilliant enough to be seen in daylight. For reference, that star to the upper left of the satellite is Vega, one of the brightest, and is many times fainter than this satellite. Visit heavens-above.com for info on satellite visibility predictions for your area.