NEW YORK (AP) -- People around the world were up at the crack of dawn on Friday to celebrate the longest day of the year in the Northern Hemisphere. Thousands of people from the steel canyons of New York to the stone figures of England took part in solstice celebrations marking the beginning of summer, while south of the Equator, celebrants marked the official start of winter. In England, more than 20,000 people gathered to see in the dawn at Stonehenge, police estimated. Although cloud cover prevented bright sunshine, a joyous spirit prevailed with music and dancing. In New York City's Times Square, more than 15,000 yoga enthusiasts signed up to roll out mats from 7:30 a.m., with classes going all day. "It's a counterpoint to the other big solstice celebration, New Year's Eve," said Tim Tompkins, president of the Times Square Alliance and co-founder of the event. At America's own version of Stonehenge -- the Permian Basin replica in Odessa, Texas -- a small group of high school students and about 25 other early risers got the chance to greet the sun. Other quirky American celebrations included a naked solstice festival bike ride in Seattle. In Memphis, Tenn., summer weather was right on time. The Shelby County Health Department had to put out a caution on Friday reminding residents to take care in the heat. The National Weather Service office in Memphis said heat indexes in the mid-90s are anticipated into next week. Friday is the shortest day of the year in the Southern Hemisphere, and also New Year's Day for the indigenous Aymara people of the highlands of Bolivia. Musicians played flutes and drums during a winter solstice ritual as the first rays of sun hit the ruins of the ancient city Tiwanaku.