NASA's Earth observation satellites (Photo : NASA)
There are some 1,235 man-made operational satellites orbiting the Earth doing a lot of jobs that keep us safe, sound and fed. United States' satellites account for over half this total.
We know they're up there but we can hardly visualize how they zip through outer space -- until now.
NASA went through great lengths to create a video animation showing and identifying 19 of its Earth-observing satellites that flash over the Earth multiple times per day in polar orbits. The video also shows brief appearances by the International Space Station and a SpaceX probe called SMAP.
NASA's "birds" often pass within just a few dozen miles of each other as they make their hour-and-a-half trip across Earth at 400 miles.
The video was created by NASA's Scientific Visualization Studio. It features the paths of 19 different NASA satellites that monitor conditions on the planet's surface.
Noteworthy are four satellites traveling together in the same orbit: Aqua, Aura, CloudSat and Calipso.
These environmental-monitoring satellites are part of what NASA calls the "A-Train." This group holds 15 different instruments that study 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".
These satellites have different tasks. Some measure precipitation from rainfall to snowfall. Others observe ocean surface levels and salinity; solar heat absorbed by the Earth's surface and other meteorological and climate changes.
