- From down here on the ground, space looks like a pristine void. But Earth's orbit is actually crowded with a ton of stuff, from human-made satellites to many smaller pieces of debris whirling around at dangerously high speeds, as the film Gravity so memorably dramatized. In fact, there are an estimated 500,000 or so smaller orbital debris (between one and 10 centimeters in diameter) and about 21,000 larger bits (larger than 10 centimeters) spinning around Earth right now, according to NASA's Orbital Debris Program Office.
There's a cooler version of this from Trimble or something like that whose name I always forget. I just tried to find it in my passwords and what I came up with is Space-Track.org, which I think you need a DoD clearance for (I remember getting the TLE data was a bitch). francopoli which is the one I'm thinking of?
The one I always use is Heavens Above But wait, there is even cooler stuff out there! want to see if the ISS is going to pass in front of the sun or moon? There is a page for that! Want to have a quick look at the weather, and see if there is going to be an ISS pass visible? Clear Outside has you covered! Want to find a nice dark spot to see a meteor shower? Dark Site Finder has the most current light pollution maps, but be warned they are still out of date and the sky will be brighter in most spots than the maps say. They also have, under the 'Weather' tab a good guess as to water vapor and cloud cover for the next week. And then you have the astronomy standard of Clear dark Sky which will only do weather and a guess as to light pollution levels based off the 2001 (not 2012) map. I'm sure there are more satellite pass predictors out there but Heaven's Above is the one that has the API that the Apps use. And it does Iridium Flares.