On February 11, 2015, DSCOVR was finally lofted into space by a SpaceX Falcon 9 rocket. After journey of about 1.6 million kilometers (1 million miles) to the L1 Lagrange Point, the satellite and its Earth Polychromatic Imaging Camera (EPIC) has returned its first view of the entire sunlit side of Earth. At L1—four times farther than the orbit of the Moon—the gravitational pull of the Sun and Earth cancel out, providing a stable orbit and a continuous view of Earth. The image above was made by combining information from EPIC’s red, green, and blue bands. (Bands are narrow regions of the electromagnetic spectrum to which a remote sensing instrument responds. When EPIC collects data, it takes a series of 10 images at different bands—from ultraviolet to near infrared.)
So why is the “Blue Marble” a bigger deal than these? Turns out, it’s quite tricky to take a good photo of the entire Earth.
The first challenge is that our planet is big. The only way to view all of it at once is to get much farther away from the Earth than we do for many of our activities in outer space. The International Space Station, for instance, orbits at a height of just 400 kilometers, or about 249 miles away from Earth.
The second problem is a familiar one that plagues many photographers who are Earthbound: lighting. In order to view the Earth as a fully illuminated globe, a person (or camera) must be situated in front of it, with the sun directly at his or her back. Not surprisingly, it can be difficult to arrange this specific lighting scheme for a camera-set up that’s orbiting in space at speeds approaching thousands of miles per hour.
As a result of these challenges, NASA, NOAA, and other science agencies most often rely on composite images to depict our planet. These images stitch together multiple high-resolution snapshots taken by satellites already in orbit to produce one seamless portrait of the Earth. And that’s what the three photos above are: composite images produced by NASA over the past fifteen years (released respectively in 2002, 2007, and 2012).