Cirrus clouds are thin, high-altitude clouds. They can be so thin that they are often invisible to the naked eye, but the moderate resolution imaging spectroradiometer on NASA's Terra and Aqua satellites can capture them with ease. These clouds are particularly important to observe because they play a key role in the greenhouse effect. Cirrus clouds allow most of the sun's light to pass through them, but they also help catch heat rising from the Earth's surface.
Shown here is the cirrus reflectance from September 2014. Bright white pixels in these images are regions completely covered by cirrus clouds. Interestingly, airplane contrails can help form more cirrus clouds than nature would on its own, meaning that this map is also an important way of monitoring human-caused cirrus formation across the globe.