In the age of the camera phone, it's human nature to snap away at anything unusual. Those passing through Rockefeller Center over the next seven weeks will no doubt fall prey to that temptation when they encounter "Human Nature," a constellation of nine towering bluestone figures that the artist Ugo Rondinone has set on the plaza in front of 30 Rock. No sooner were the giant evocations of fossilized humanity unveiled than they acquired a nickname. "It's Ugohenge," the painter Elizabeth Peyton said at a dinner at the Monkey Bar last Tuesday to celebrate the show's opening. Isn't that what everyone's calling them? The craggy colossi do suggest an urban Stonehenge. When the sun is high, they cast almost mystical shadows across their 6,700-square-foot poured concrete base. At 16 to 20 feet tall and weighing up to 30,000 pounds each, the figures stand as centurions of public space, formidable yet approachable. "People have been hugging them," said Nicholas Baume, director of the Public Art Fund, which commissioned the project with Tishman Speyer, Rockefeller Center's primary owner. Still, cuddly they're not. The coarse stones, veined by quartz and set one atop the other in post-and-lintel fashion, have been cut so unevenly that they appear to have been gnawed into shape. Yet the rough texture invites caressing. Rondinone's goal wasn't to inspire affection but to create a juxtaposition of the ancient and the modern. The figures" compatibility with the surrounding architecture stems from the stone Rondinone used, which comes from the same Pennsylvania quarry that provided the plaza's pavement. "That was pure chance," Rondinone said. The Swiss-born artist, who has lived in New York since 1998, has worked in wax, lead, bronze, stained glass, paint and earth to make his paintings, objects and installations, but this was his first foray into stone. "It's a very primal material," he said. The titles he gave the figures - including "Sad," "Calm" and "Ecstatic" - are just as elemental. And because the sculptures are impassive, with upright stones for heads, fat slabs for torsos and sturdy plinths for legs, they become blank slates that elicit an emotional response from viewers. It was so chilly and blustery on the plaza Tuesday evening that my first impulse was to use them as a windscreen, then huddle against them for warmth. According to Baume, more than 15 million people will pass by them before the exhibition closes on June 7. The sculptures" fleeting life only adds to their humanity, while giving them an immediacy that few public artworks possess. Most often, they are stolid monuments loved more by pigeons than by people. But with organizations like the Public Art Fund, Creative Time, the Art Production Fund and High Line Art ramping up their efforts to bring contemporary art to our streets, parks, billboards and other open spaces, the whole city has become a pop-up gallery offering welcome, entertaining and photogenic intrusions on everyday routines. Rockefeller Center won't be the only place to commune with Rondinone's work this spring. Two other exhibitions, both titled "Soul," will feature more modestly scaled figures. One opens May 11 at the Barbara Gladstone Gallery in Chelsea, the other on June 8 at the Eva Presenhuber Gallery in Zurich. By then, Rondinone's taller totems will be gone from 30 Rock and live only in the popular imagination, racking up likes on Instagram and Tumblr, waiting for a new day in the sun. Ugo Rondinone's "Human Nature" is on view at Rockefeller Center Plaza, between 49th and 50th Street, through June 7.