DISCOVR and EPIC Observe the Earth and the Far Side of the Moon
August 10, 2016
August 10, 2016
Summary Authors: Jim Foster; Dave Lynch; NASA Earth Observatory
The image above showing a comparison of the Earth and the far side of the Moon was acquired by NASA’s Earth Polychromatic Imaging Camera (EPIC) on NOAA's DSCOVR satellite. DISCOVR orbits approximately one million miles (1.6 million km) from Earth -- it's more than four times further out than the Moon. As it does, EPIC maintains a constant view of the fully illuminated Earth. However, two or three times a year it images both the Moon and Earth together. When this happens, EPIC is observing the Moon's far side. Note that since the Moon’s orbital period is the same length of time as its rotation, observers on Earth always see the same side (near side) of the Moon.
On this image, acquired on July 5, 2016, Australia is toward the bottom of the blue marble and Asia is at left, TheArabian Peninsula is at far left. These landmasses appear about the same in brightness as the lunar surface. But the reflectivity of the Moon is only around 12 percent (expressed as the Bond albedo), whereas the Earth's is closer to 30 percent. The Earth's continents are slightly more intrinsically brighter than most lunar surfaces. This is because the sand and barren ground characteristic of arid regions covering much of Australia, Africa, North America and Asia are more reflective than the basaltic lava and anorthosite that compose the majority of the lunar plains andhighlands, respectively.
Of course, ice and snow (fresh snow has a bond albedo of 84 percent), in the Arctic and Antarctic regions and covering much of the Northern Hemisphere during the winter season drastically increases the Earth's overall brightness. Clouds, nearly as reflective as fresh snow, also make Earth considerably brighter than the Moon.
Photo Details: EPIC is a four megapixel CCD camera and telescope. Its natural-color images are produced by combining three separate monochrome exposures taken in quick succession. It's worth noting that the relative sizes of the Earth and Moon are not quite right as shown because the Moon at conjunction is closer to EPIC than is the Earth. The true size of the Moon compared to the Earth would be about 75 percent of what is shown in the image.