Looking up at the blue sky on a cloudless day, it's easy to forget that there are hundreds of satellites zipping by overhead. A recently released NASA animation certainly reminds us of that fact.
The video, created by NASA's Scientific Visualization Studio, features the paths of 19 different satellites used by the agency to monitor conditions here on Earth -- including the Cloud-Aerosol Transport System mounted on the International Space Station.
Of particular note are four satellites that travel together in the same orbit: Aqua, Aura, CloudSat and Calipso. These environmental-monitoring satellites are part of what NASA calls the "A-Train," and together they hold 15 different instruments useful for studying such things as rainfall and aerosols in the air. They get their name because they cross over the equator each day at 1:30 p.m., so the "A" stands for "afternoon."
Looking at this animation, you might be surprised by just how crowded the satellite space around our planet is. But remember, this animation only shows 19 Earth-observing NASA satellites. According to a roundup of all satellite launches through summer of last year by the Union of Concerned Scientists, there are actually 1,235 satellites soaring around the planet. That's over 100 times the traffic you see in this NASA video.
I may never look at a blue sky the same way again.