Every full moon, Landsat 8 turns its back on Earth. As the satellite's orbit takes it to the nighttime side of the planet, Landsat 8 pivots to point at the moon. It scans the distant lunar surface multiple times, then flips back around to continue its task of collecting land-cover information of the sunny side of Earth below.
These monthly lunar scans are key to ensuring the land-imaging instrument (the Operational Land Imager) aboard Landsat 8 is detecting light consistently. For this, engineers need a consistent source of light to measure. And while there are some spots on Earth – like the Sahara Desert or other arid sites - that reflect a relatively stable amount of light, nothing on our planet beats the moon, which lacks an atmosphere and has an unchanging surface, barring the odd meteorite. The Landsat Program is a series of Earth-observing satellite missions jointly managed by NASA and the U.S. Geological Survey. The first Landsat satellite launched in 1972 and Landsat 8 launched on February 11, 2013.