On August 18, 2002, asteroid 2002 NY40 passed within 325,000 miles of Earth.
If this fact doesn't scare you just a little bit, it should. This is a
near-miss - it passed just 1.3 times farther from the Earth than the distance
to the Moon.
2002 NY40 is an example of a Near-Earth Object, or NEO, and is one of
thousands of these space rocks that range in size from a few feet
up to a mile or more across.
This one is about 2200 feet in diameter. Should it hit the Earth, it
would blast a crater about 4.4 miles across.
Though 2002 NY40 is small compared to the asteroid that killed the
dinosaurs 65 million years ago, it still represents a threat - if it
hits a city, it would create a natural disaster unlike
any in recorded history, equivalent to 50,000 Hiroshima-type bombs.
This image is actually a series of short (1 second) images, with 1 second in
between - it took just 90 seconds for the asteroid to cross this field... it
was moving so quickly across the sky that it moved the diameter of the full
moon in a bit less than 4 minutes!
2002 NY40 does not pose a threat in the future, according to calculations.
But keep in mind that most NEOs are found after they've already
passed close to the Earth...