On 1/19/14, telecommunications satellite Iridium 14 passed 769 km overhead Golden, CO, slowly rotating about its longitudinal axis at an azimuth of 044° (NE) and altitude of 66.8°. At 17:42:49, the satellite’s left antenna, a door-size reflective panel, reflected the sun’s light directly onto our location here in Mountain Ridge, resulting in an estimated -7.7 magnitude ‘flare’, manifesting as the line of light you see in the image below. For reference, Venus is a -5 magnitude, while the ISS at its brightest is -6 (the full moon is brighter at -13); thus, this flare was nearly 4 times brighter than the brightest the ISS can ever be. That’s bright! It’s reported that Iridium flares can rarely be as bright as magnitude -9, and if one is located directly on the centerline of such a transit in an optimal dark-sky location, you could theoretically see the terrain around you light up a bit, similar to a quick swath of dim moonlight.
The following is the full frame image, shot with a 5D MkIII and 24mm lens (25 sec., f/5.0, ISO 50):