This star chart shows the track of asteroid 2004 FH at the time of closest approach as it sped by Earth on the night of March 18-19. Sadly, the object was not well placed for U.K. observers, skimming the southwest horizon when at its brightest. Image credit: Astronomy Now

Discovered by astronomers of MIT's Near-Earth Asteroid Research (LINEAR) survey just two days previously, this house-sized body made the closest flyby of Earth ever predicted at 10 p.m. (GMT) on March 18th. It missed us by just 26,500 miles — one ninth the distance of the Moon.

Since it is so small and passed so close, the apparent brightness of 2004 FH varied tremendously during its few hours of fame, reaching a peak of about visual magnitude +10 by 9 p.m. GMT.

Its apparent path against the stars for an observer situated close to the centre of the British Isles is shown at hourly intervals around the point of closest approach, when it traversed the apparent width of the Full Moon every minute. For an observer watching through a telescope, the motion would be immediately obvious.

Unfortunately for U.K. observers, the viewing prospects were not good. The asteroid skimmed the southwest horizon when at its brightest, and by dusk on March 19th it will have faded to magnitude +20 as it recedes from Earth in the direction of northern Cetus.

Given the orbit now determined for 2004 FH, it appears to belong to the Aten class of asteroids. It takes nearly nine months to orbit the Sun in a plane close to that of the Earth. The asteroid is currently near aphelion (furthest from the Sun in its orbit), but its noticeably eccentric path can take it inside the orbit of Venus.