Shuttle Over Earth

Explanation: What's that approaching? Astronauts on board the International Space Station in 2010 first saw it far in the distance. Soon it enlarged to become a dark silhouette . As it came even closer, the silhouette appeared to be a spaceship. Finally, the object revealed itself to be the Space Shuttle Endeavour , and it soon docked as expected with the Earth-orbiting space station. Pictured here , Endeavour was imaged near Earth's horizon as it approached, where several layers of the Earth's atmosphere were visible. Directly behind the shuttle is the mesosphere , which appears blue. The atmospheric layer that appears white is the stratosphere , while the orange layer is Earth's Troposphere . Together, these thin layers of air -- collectively spanning less than 2 percent of Earth 's radius -- sustain us all in many ways, including providing oxygen to breath and a barrier to dangerous radiations from space .

Coming up Friday: Earth Day 2022