Quarter-mile asteroid passes Earth
An asteroid as big as an aircraft carrier has passed by Earth 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 11.28pm GMT. That is 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 it will not 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 29,000mph.
Astronomers and amateur skygazers around the world kept watch too.
The Clay Centre Observatory in Massachusetts planned an all-night viewing party so children and parents could peer through research-grade telescopes and listen to lectures. The asteroid cannot be detected with the naked eye.
For those without a telescope, the observatory streamed video of the fly-by 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 that there are things out in space that we need to be aware of," including this latest fly-by, said observatory director Ron Dantowitz. Mr Dantowitz added: "It will miss the Earth. We try to mention that in every breath."
If an asteroid that size would hit, 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 70ft tsunami waves.