When reference librarian Anders Kvernberg posted a different page from this atlas on Reddit, neither he nor any of the commenters knew just how rare the book was. Nikolaj Blegvad

Anders Kvernberg was deep in the vaults of the National Library of Norway when a beautiful atlas caught his eye.

So, you know. "It was an ordinary day at work," he says.

As a reference librarian, Kvernberg spends his days digging through the library's collections to answer questions from the public — on absolutely any topic. Writing a history book and want to know when a train would run from city A to city B on a particular year? "We find the old timetables," he says.

He was chasing down an unrelated request last month when he saw the atlas. He couldn't read the title or any of the text, but he could make out the printing year, and could identify it as an Ottoman atlas — a very, very early Ottoman atlas.

"And on top of that it was a beautiful copy — it was hand-colored, it had very nice printing, so it was fascinating," he said.

Kvernberg is a self-described map nerd. He's also an avid contributor to Reddit, the social-sharing site with a community for nearly every imaginable interest. So he figured he'd scan a few pages from the atlas and upload them to /r/MapPorn — the subreddit for sharing striking images of maps. "Ottoman world map, 1803": People commented, Kvernberg got some upvotes. So far, so typical. But a few weeks later, Kvernberg was browsing /r/MapPorn when he saw something familiar: a page from the same atlas he'd scanned, uploaded by someone else. And this time, one of the commenters had identified the title: the Cedid Atlas Tercumesi, one of the first printed atlases from the Muslim world. Only 50 copies had ever been printed, and only 14 were known to still exist.

Kvernberg went back for a second look at his find, and then he posted on Reddit again.

The Cedid Atlas Turcumesi, or New Atlas, drew on William Faden's General Atlas for cartographic details, according to the Library of Congress. Nikolaj Blegvad

"Wow," he said. "That number is now 15."

The Norwegian copy was inventoried in their card catalog, but not in their digital catalog, so no one outside the library knew it existed. And no one inside the library, apparently, knew it was so rare.

"I ran to my boss, of course," Kvernberg says. That would be Benedicte Gamborg Briså, a research librarian and historian who's the in-house expert on maps.

"This wasn't the first time he came running with something and said, 'Ah, look at this!' " Briså says. "So, I looked at it."

Reference librarian Anders Kvernberg (right) discovered the Cedid in the library's vaults. Research librarian and map historian Benedicte Gamborg Briså (left) confirmed its authenticity. Nikolaj Blegvad

The paper, the marks from the printing plate and the binding all confirmed it was an original copy, not a later duplicate.

So what was a rare turn-of-the-19th-century Ottoman atlas doing unnoticed in the vaults of the National Library of Norway? Fortunately, there was a reference librarian on hand to track down the details.

"There's a name written inside, which is probably the previous owner. He was a textile importer from Oslo," Kvernberg says.

"And I found out that he did travel in the Balkans in the late 1930s. He visited Albania and southern Yugoslavia ... which were part of the Ottoman Empire at the time the book was printed."

They suspect he bought the atlas there — a stroke of luck for the book.

"It was in 1937 — and this was just a couple of years before the Nazis invaded Yugoslavia, which led to widespread material destruction throughout the country. So it's possible that when this guy bought it and brought it out of the country, he may just have saved it from destruction."

Browsing Reddit weeks after he stumbled across a beautiful atlas in the vault, Anders Kvernberg discovered it was just the 15th surviving copy in the world. "It was a beautiful moment," he says. Nikolaj Blegvad

It was probably donated to the library in the early 1950s — another lucky break, Kvernberg says.

"It ended up here 60 years ago. It went into a controlled environment where air and light, humidity, temperature, everything's been specifically set for preserving paper. Had it ended up in a basement or something like that, it would probably have rotted away or somehow been destroyed by now.

"Fifty of them were printed, and this is the 15th known copy — so 35 of them were not so lucky."

Now the atlas is heading to the library's preservationists.

"Most probably, when they're done with it, we will digitize it and put it online for everyone to enjoy," Kvernberg says.

The National Library of Norway is currently immersed in a massive digitization project, pushing books and other library materials out onto the Internet. Kvernberg says the same philosophy is why he regularly takes time out of his day to scan pages and upload them to Reddit — not, in most cases, undiscovered treasures, but "just ordinary stuff that's beautiful or interesting." "I believe that we should show off the stuff that we have," he says. "Because we keep it locked up in vaults to preserve it, but that doesn't mean people shouldn't see it." Copyright 2019 NPR. To see more, visit https://www.npr.org.