U.S. astronaut Scott Kelly has retired from NASA, after 20 years of service and more than 520 days in space—more time in space than any other American. He also departs with a record as a social media maven and renowned photographer from space.

Kelly made four trips to space, the most prominent being a 340-day journey that ended last month. During that flight, Kelly made more than 5,000 trips around the Earth, and drank nearly 200 gallons of drinking water made from recycled sweat and urine.

From his perch 400 kilometers (249 miles) above the earth’s surface, he snapped hundreds of beautifully abstract photographs of our planet’s landforms and waterways. He spotted hurricanes ominously swirling on sapphire-blue oceans. He gazed out at the aurora’s glittering fog. He consistently turned Earth’s lands and waters into an abstract artist’s dream, with shots of beaches, deserts, forests, and everything in between.

And he did it all with equipment accessible to earthlings, taking most of his images with a Nikon D4 digital camera with lenses more commonly used to photograph football games.

Kelly’s photographs gained him a massive following. From Twitter to Tumblr, hundreds of thousands of social media users expressed their wonderment at the photos—and a devoted band of mapping experts tagged along, helpfully noting where Kelly snapped his pics.

“It’s fun to be a part of the public’s reaction,” says David MacLean of Nova Scotia Community College’s Centre of Geographic Sciences, who’s among the most influential of Kelly’s hobbyist geotaggers.

MacLean has been mapping astronauts’ photos since 2013, but says Kelly’s penchant for abstraction sets his pictures apart.

“Other astronauts have more of a city and regional view: ‘Here’s Indianapolis from space,’” MacLean says. Kelly, on the other hand, “has concentrated on details of little pieces of the world.”

“He’s caught the interest of quite a lot of people, [who] see these [places] in a whole new way.”

And Kelly’s eye for composition hasn’t gone unnoticed at National Geographic.

“Kelly’s photographs are striking and incredibly artistic," wrote Patrick Witty, National Geographic’s deputy director of photography. “[It’s] hard to believe they were made by an astronaut and not a working professional photographer.”

“I’m sure every photographer on Earth is incredibly jealous of his angle.”

To celebrate Kelly’s #YearInSpace, we’ve selected our favorite Scott Kelly space pictures. We hope you enjoy the photos—and check out National Geographic's photographic coverage of Kelly’s final return to Earth.