Asteroid 2011 GP59 spins right round baby right round
The asteroid 2011 GP59 is a small rock with an orbit that takes it from just inside the orbit of Venus to just outside that of the Earth. On April 15th at around 19:00 UTC, it’ll cruise by us at a distance of about 533,000 kilometers (330,000 miles) — farther away than the Moon. This asteroid poses no threat to us, but because it does get relatively close, amateur astronomers have been able to capture it in their telescopes.
In fact, Nick James of Chelmsford, Essex, England, took a series of images on April 11, 2011 and made this video:
You may have to watch it more than once; the asteroid starts in the center of the frame and moves to the lower right. The stars appear to move as the telescope tracks the asteroid, so it can be tricky.
See how the asteroid appears to wink on and off? It’s spinning as it orbits the Sun, and must have an elongated shape. When we see the side of it we see a bigger area, which means it reflects more light and it looks brighter. When the narrow part is pointed toward us the area is smaller, and it looks dimmer. The overall size is something like 50 meters in diameter, but given the change in brightness as it spins — by a factor of over 6 times! — it must be quite elongated, more cylindrical than spherical.
Even at closest approach you’d need a decent telescope to even see GP59. Still, it’s pretty neat that we can learn so much about this rock just from a few observations, even when it was still millions of kilometers away.