Exploring Earth’s Limb

Detecting gas molecules where they occur at different heights in the atmosphere requires going out on a limb—Earth's limb. From orbit, Earth's limb is the fuzzy blue halo that appears above the surface. Instruments like the Microwave Limb Sounder on NASA's Aura satellite observe the limb to get a side view of the atmosphere from the ground to where it thins out into space. This perspective allows scientists to measure atmospheric chemistry layer by layer—essential for monitoring the gases that contribute to the hole in the ozone layer and for evaluating the impact of clouds on climate change. The Microwave Limb Sounder was the first to measure, from space, all the gases that are part of the ozone depletion cycle, giving scientists the first observations that revealed the full chemical process of ozone depletion as it occurs. Explore the images for views of different gases observed by the satellite visualized on a globe.