Sky Tracker is a popular app that lets you identify different stars and constellations in the sky. In addition to tracking celestial objects, Sky Tracker also identifies any man-made objects in the sky, including the International Space Station, satellites, and space debris. Lots and lots of space debris.
In an article published in September of 2013, NASA believes that there are over 500,000 pieces of space junk orbiting the planet, of which 20,000 are bigger than a softball. The debris consists of excess electronics and equipment, including decommissioned satellites, abandoned launch stations, and mission-related debris. The space junk are traveling at a speed of 17,500 mph (28,165 kmph), posing a threat to any manned space missions, particularly the International Space Station.
At this speed, a tiny paint fleck could pose serious damage to the space craft. NASA has had to replace several shuttle windows because of damage caused by orbiting paint flecks.