At first glance this pixelated picture may not look all that spectacular, but it gains a whole new meaning when you realize what it’s actually showing: a look at the most distant crescent moon ever seen! But this isn’t Earth’s moon; it’s Charon, Pluto’s largest companion, lit by the light from a Sun 3.2 billion miles away—some of it even reflected off Pluto.
NASA’s New Horizons spacecraft obtained this image with its Ralph Multispectral Visible Imaging Camera on July 15, 2015, a day after its closest approach to the distant planet. New Horizons was about 100,000 miles beyond Pluto and Charon by that point; the only way to truly get a crescent moon picture is to be farther from a world than the Sun!
The right limb of Charon is lit by sunlight; the upper left hemisphere is lit by reflected sunlight off Pluto. Stars are visible in the background.
This isn’t the first crescent picture of Charon to be released; New Horizons’ LORRI camera also captured an image of the moon in crescent taken two days later from 1.9 million miles away:
At 750 miles across Charon is half the size of Pluto, making the two worlds more of a binary system than a typical planet-and-moon pair. In fact they both orbit a point between each other, and are also tidally locked…as Pluto and Charon travel around the Sun in their 248-year-long orbit—with four other miniature moons in tow—they both always show the same face to each other.
Source: New Horizons/JHUAPL