The Iridium communication satellites have a peculiar shape with three polished door-sized antennas, 120° apart and at 40° angles with the main bus.
Occasionally, an antenna reflects sunlight directly down at Earth, creating a predictable and quickly moving illuminated spot on the surface below of about 10 km diameter. To an observer this looks like a bright flash, or flare in the sky, with a duration of a few seconds.
This app displays in real-time where is each Iridium satellite, predicts when these flares will occur from the observer's position and allows from the 3D locator, locate the exact point in the night sky.
Gets the data needed from android device (accelerometer, compass, location) and from the following urls:
www.celestrak.com and www.heavens-above.com