For four decades, the Landsat program has been documenting Earth from space. Satellites gather light from both visible and invisible parts of the electromagnetic spectrum to craft detailed images including human, biological, and geological details.
This is the first Landsat satellite's first photo ever. It shows Dallas, Texas, on July 25, 1972, exactly 40 years ago.
Because Landsat satellites have been gathering visual information for four decades, we can now view landscapes before, during, and after fires and other natural disasters, and see bodies of water shift their shapes as water levels rise and fall, and watch cities grow.
For example, 1972 wasn't the last time that Dallas fell into Landsat's sights. Subsequent pictures show the metropolis' fast growth these past few decades.
Many of these images come from NASA's "Earth as Art" contest. Out of 120 beautiful Landsat images, people voted for their favorites; the five top ones are included in this gallery.
Lake Eyre sits in the northern desert region of South Australia, a primarily arid state. Although one of the world's largest internally draining systems empties into the lake, Eyre fills up completely only a few times every hundred years. When full, it's the largest lake in Australia. But when the water levels are low, as in this image, it looks more like a creepy face foaming at the mouth.
This picture could be an abstract painting--but those yellow stripes are sand dunes, not paint. This is a picture of Erg Iguidi, a Saharan "sand sea" that stretches from Algeria to Mauritania.
An erg is a sheet of constantly shifting sand--in fact, ergs contain 85 percent of the moving sand on Earth. From far above, Erg Iguidi seems to be composed of wispy, delicate strands of sand, but don't be fooled: its individual dunes can be more than third of a mile high and wide.
The left part looks like an unfortunately pixelated photo, but the square shapes are actually towns and fields around the Mississippi River. This Landsat image, located on the Arkansas-Mississippi border, shows the twists, turns, and oxbows of North America's biggest river system.
The branching waterways of Alaska's Yukon Delta resemble nerve networks or arteries in a body. But although this picture might be mistaken for a cross-section of living tissues, those tissues would have to belong to one enormous being: The delta is about the size of Oregon.
The winner of the Earth as Art contest certainly deserves its #1 position. Around Gotland, Sweden's largest island, phytoplankton form green whorls in the dark sea. The tiny plants reached this visible level of growth after currents dragged nutrients from the water's depths to its surface.