Physics Photo of the
November 11, 2011
Asteroid 2005 YU55
Last Tuesday evening (November 8, 2011) we had
the rare opportunity to view an asteroid as it zipped past the
Earth at about 3/4 the distance to the Moon. Astronomy
students Brandon Knutson,
Katie Anderson, and Josh Jenkinson assisted in capturing a series
of telescopic images of this asteroid. Although the
asteroid was bright as asteroids go, it still required a
telescope to observe. The above photograph is a sum of
about 40 5-second exposures as the asteroid swept past the
field of view of the telescope camera in a period just under 5
minutes. According to NASA the asteroid is about 800
meters (1/2 mile) in diameter. The Moon was very bright
that night as well, making the background sky rather
bright. The narrow "squiggly" lines throughout the image
are scattered "hot pixels" in the camera. In the excitement we forgot to turn on the
camera cooling mechanism, which would have virtually
eliminated the hot pixels. The "movement" of the hot
pixels is an artifact. The telescope is clock-driven to
keep up with the stars, but the guiding is not perfect.
The stars move slightly relative to the hot pixels. The
stack of images was aligned with the stars, thus
causing the hot pixels to appear to move.
The animated pigure at the right shows a succession of
alternate 5-second exposures played back at about 20 times the
real-time speed. It was amazing to sit at the telescope
and computer monitor watching the star-like object move
to a new position with every 5 second image. Of course
the images of the asteroid are elongated because of its
continual movement during the 5 second exposures.
NASA keeps close watch on asteroids and other objects that
come anywhere near to Earth's orbit. The orbit of 2005
YU55 is so well-known that there is no chance of any
devastating collision with Earth within the next 100 years
Special thanks are also extended to physics assistant Mayuri Patel for repairing
the electrical circuit that supplied power to the telescope
earlier that day.
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