The Hubble Space Telescope has helped discover a new moon orbiting Neptune, NASA announced.

The moon is the 14th moon found to be orbiting the planet. It's only 12 miles across, making it Neptune's smallest know moon. It was spotted by Mark Showalter from California's SETI Institute, who was studying the rings around the blue planet.

The moon - named S/2004 N 1 - is 100 million times fainter than the faintest star that can be seen with the naked eye, NASA said. Even NASA's Voyager 2 missed it when studying Neptune's moons and rings back in 1989.

This time around, Showalter tracked the movement of a white dot that appeared in 150 photographs taken by Hubble between 2004 and 2009. That white dot appeared 65,400 miles away from Neptune - between the orbits of the Larissa and Proteus moons. Ultimately, he determined that it completed one revolution around Neptune in 23 hours.

"The moons and arcs orbit very quickly, so we had to devise a way to follow their motion in order to bring out the details of the system," he said in a statement. "It's the same reason a sports photographer tracks a running athlete - the athlete stays in focus, but the background blurs."

In a blog post, Showalter likened it to the work of Eadweard J. Muybridge, an English photographer who successfully used multiple cameras to make it appear as though images were moving - most notably a horse. Though photography has evolved over the years, "one truth about action photography has never changed - you need to follow the motion," Showalter wrote. "Otherwise, you will get nothing but a blur. Save your tripod for subjects that are willing to sit still. Had Muybridge attempted the same photo sequence without all those separate triggers, his image would have [been] all background, no horse!"

Similar to that horse, moons are also "like fidgety children" - unwilling to sit for the camera, Showalter wrote. S/2004 N 1 "has a special distinction - it never sits still long enough to have its picture taken. Neptune is a big planet with a strong gravity field, and moons whip around it very fast. This one circles the entire planet, following a path of over 600,000 km, in less than a day."

Still, moons are at least predictable - unlike children and horses. "We might not know where the moons are, but we do know how they move," Showalter wrote.

"As a result, we were able to write software to do all the motion-tracking, by letting a computer shift and add up the images after the fact," he said. "The procedure I devised predicts where any given moon ought to move from one image to the next, and then combines the images with a 'twist' that compensates for the expected motion."

Showalter was originally using this model to study arcs in the rings of Neptune, but decided to expand his field of view - and that's when "an extra little dot turned up."

Showalter acknowledged that the discovery "might not be Earth-shaking," but it helps tell the story of Neptune, he said. He also promised that the new moon, which is almost 3 billion miles away from Earth, will "get a better name soon."

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