LOS ANGELES – An asteroid as big as an aircraft carrier zipped by Earth on Tuesday in the closest encounter by such a massive space rock in more than three decades. Scientists ruled out any chance of a collision but turned their telescopes skyward to learn more about the object known as 2005 YU55.

Its closest approach to Earth was pegged at a distance of 202,000 miles at 6:28 p.m. EST. That’s just inside the moon’s orbit; the average distance between Earth and the moon is 239,000 miles.

The last time a large cosmic interloper came that close to Earth was in 1976, and experts say it won’t happen again until 2028.

Scientists at NASA’s Deep Space Network in the California desert have tracked the quarter-mile-wide asteroid since last week as it approached from the direction of the sun at 29,000 mph.

Astronomers and amateur skygazers around the world kept watch, too, for the asteroid, which can’t be detected with the naked eye.

The Clay Center Observatory in Brookline, Mass., planned an all-night viewing party for children and parents. For those without a telescope, the observatory streamed video of the flyby live on Ustream, attracting several thousand viewers. The asteroid appeared as a white dot against a backdrop of stars.

“It’s a fantastic opportunity to educate the public,” said observatory director Ron Dantowitz, ading: “It will miss the Earth. We try to mention that in every breath.”

If an asteroid that size would hit the planet, Purdue University professor Jay Melosh calculated the consequences. The impact would carve a crater four miles across and 1,700 feet deep. If it slammed into the ocean, it would trigger 70-foot-high tsunamis.