How amateur satellite trackers are keeping an 'eye' on objects around the Earth

Around the planet, a loosely knit but closely woven band of amateurs monitor the whereabouts of satellites — be they secretive spacecraft, robotic space drones, rocket stages, orbital debris or lost-in-space planetary probes. But what's the motivation behind this group of sky prowling spirits? What kind of tools are they using now or in the future to purge secrets from space — at times revealing what some countries don't want others to know about? More

(Source: Space.com - May 3)