I used my DSLR camera on a fixed tripod with no tracking for this image, so exposure with my chosen 50 mm lens was limited by the "500 rule"" to 500/50 = 10 seconds. I chose 8 seconds.
Visually this was an astonishing, eye-catching, bright flare, about one hundred times brighter than Sirius, the bright star top left. Sirius has a magnitude of -1.5 and is the brightest star in the entire night sky. Note that in this image, the light from Sirius is concentrated in one spot for the entire exposure of twenty-four seconds. Compare the brightness intensity of Sirius with how bright any part of the Iridium Flare is at any instant as it moves cross the image
This image consists of three stacked exposures, each of eight seconds duration and a delay of around one second between each, hence the two gaps in the trail.
Image (c) R.Powell - click for enlargement
DETAILS:
Date: 23rd February 2016.
Time: 8.45 pm
Source: Iridium 25 MMA2 left antenna.
Predicted flare magnitude: 7.0
Flare predicted for my location by Calsky.com
Satellite height above Earth: 791 km.
Satellite distance from camera: 904 km.
Objects also in image: Sirius (top left, mag 1.5) and M46-M47 (lower centre) open star clusters.
Constellations in image: Canis Major and Puppis.
Exposure details: 3 x 8 sec, 50 mm, f/3.2, ISO 500.
Image processing: Registax and Photoshop.