Astroalert from Sky & Telescope:
======================================= This Is SKY & TELESCOPE's AstroAlert for Minor Planets =======================================
CLOSEST FLYBY EVER
Less than 24 hours from the time this message is being issued, a tiny, newly discovered asteroid will make the closest flyby past Earth that has ever been predicted by astronomers.
The object, dubbed 2004 FH, is probably only about 20 meters in diameter (the size of a house). An electronic circular issued late on March 17th by the Minor Planet Center in Cambridge, Massachusetts, indicates that it will definitely not hit the Earth. It will pass about 49,000 kilometers (30,500 miles) from Earth's center, which is one-eighth the distance of the Moon.
This object was discovered on March 16th by astronomers of MIT's Lincoln Near-Earth Asteroid Research (LINEAR) survey in Socorro, New Mexico. Further observations made on the 17th at Klet Observatory (Czech Republic), Starkenburg Observatory (Germany), and Modra Observatory
(Slovenia) helped the Minor Planet Center compute its exact trajectory.
The flyby scenario for 2004 FH goes like this:
* At 18 hours Universal Time on March 18th, the asteroid will be 12th magnitude as it glides just south of the star Spica in Virgo, heading west.
* By 22 hours UT on the 18th, it will have brightened to 10th magnitude when it passes closest to Earth in the constellation Antlia.
* At 0 hours UT on March 19th -- which is around the time darkness falls on the East Coast of North America on Thursday, March 18th -- it will have faded back to 12th magnitude as it shoots by Sirius near the open star cluster Messier 41. By then it will be receding from Earth and heading back into space.
Because 2004 FH will be passing so close, it is not practical for me to include a detailed ephemeris in this message. Its path across the sky depends greatly on an observer's vantage point on Earth (owing to the parallax effect). Observers who wish to locate it in small telescopes should use the Minor Planet Center's Ephemeris Service to make detailed predictions for their own geographic location:
cfa-www.harvard.edu/iau/MPEph/MPEph.html
According to the orbit calculated by Gareth Williams, associate director of the Minor Planet Center, 2004 FH belongs to the Aten class of asteroids. It circles the Sun in just under 9 months in very nearly the same plane as Earth's orbit. At perihelion it swings well inside the orbit of Venus; at aphelion (as currently) it ranges just outside that of the Earth.
Roger W. Sinnott
Senior Editor
SKY & TELESCOPE
  