Normally, the Lunar Reconnaissance Orbiter (LRO) has its cameras fixed on the surface of the Moon. But on May 24, 2014, flight engineers directed the spacecraft to turn back for a quick look at Earth and one of our closest planetary neighbors — Mars.
When the spacecraft's LROC camera captured this image, Earth was about 376,687 kilometers (234,062 miles) away from LRO and Mars was 112.5 million kilometers away. In other words, Mars was about 300 times farther from the Moon than the Earth. (Note: Mars has been contrast-stretched in order to improve its visibility.)
This view of Earth includes several cloud patterns that satellites observe frequently. A line of rain and thunderstorms are visible in a band near the equator, an area known as the Intertropical Convergence Zone. To the north, off the west coast of North Africa, notice the banks of closed-cell clouds over the Atlantic Ocean. Moving into the high latitudes, we see comma-shaped cloud patterns caused by extra-tropical cyclones.
LROC actually consists of two narrow-angle cameras. Images taken by these cameras are built from rows of pixels acquired one after another, and then the left and right images are mosaicked together to make a complete pair. If the spacecraft was not moving, the rows of pixels would image the same area over and over; so it is the spacecraft motion, combined with fine-tuning of the camera exposure time, that enabled the final image.
Capturing this image required some advance planning. LRO's team took practice images of Mars on May 8, 2014, to refine their timing and camera settings. 
References
Arizona State University (2014, October 2) Two-Planet Perspective from Lunar Orbit. Accessed October 10, 2014.
NASA Goddard Space Flight Center (2014, October 2) Lunar Reconnaissance Orbiter. Accessed October 10, 2014.
Image courtesy NASA/Goddard/Arizona State University. Caption by Adam Voiland.
- Instrument(s): LRO - NAC
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