"Usually, when we see an asteroid strobe on and off like that, it means that the body is elongated and we are viewing it broadside along its long axis first, and then on its narrow end as it rotates," said Don Yeomans, manager of NASA's Near-Earth Object Program Office at the Jet Propulsion Laboratory in Pasadena, Calif.
Amateur astronomers, including Nick James of Chelmsford, Essex, England, generated video of the "blinking" asteroid GP59 with an 11-inch telescope, taking 137 sequential individual frames, each requiring 30 seconds of exposure, a propulsion laboratory release said last week.
"GP59 is approximately 50 meters [240 feet] long, and we think its period of rotation is about 7 1/2 minutes," Yeomans said. "This makes the object's brightness change every 4 minutes or so."
Asteroid 2011 GP59 made its closest approach to Earth Friday at a distance just beyond the moon's orbit, about 331,000 miles, the laboratory's release said.