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View Full Version : Just In: NASA’s Latest Image of Asteroid 2005 YU55



Fraser
2011-Nov-08, 12:00 AM
NASA’s Deep Space Network antenna in Goldstone, California has captured new radar images of Asteroid 2005 YU55 as it begins its close pass by Earth. The image above was taken on Nov. 7 at 11:45 a.m. PST (2:45 p.m. EST/1945 UTC), when the asteroid was approximately 1.38 million kilometers (860,000 miles) or about 3.6 lunar [...]

More... (http://www.universetoday.com/90769/just-in-nasas-latest-image-of-asteroid-2005-yu55/)

schlaugh
2011-Nov-08, 01:28 AM
I have the same question someone else asked in another thread - if it's a radar image then why do we see shadows?

ETA: Never mind - asked and answered: http://www.bautforum.com/showthread.php/123718-Asteriod-YU55?p=1955103#post1955103

IsaacKuo
2011-Nov-08, 03:35 PM
I have the same question someone else asked in another thread - if it's a radar image then why do we see shadows?

ETA: Never mind - asked and answered: http://www.bautforum.com/showthread.php/123718-Asteriod-YU55?p=1955103#post1955103

That answer is completely wrong.

In fact, both sides of the asteroid are shown, superimposed on top of each other. This is an unavoidable artifact of the way these images are created. It's called a doppler-delay (http://planetary.org/blog/article/00002462/) image.

You see shadows because the point closest to Earth is actually the top of the image. The Y-axis is used to show the delay of the return signal. The point closest to Earth is the top. The point furthest from Earth is the bottom. The reason the bottom appears to be in shadow is because it is in shadow. It's shadowed from the radar beam by the rest of the asteroid.

This shadow effect has nothing to do with sunlight, of course. It's purely a question of which parts of the asteroid are hidden from the radar beam. The reason you're confused is because you think this image is oriented the way an image through a normal telescope would be. It isn't. Doppler-delay radar images are generated in a completely different way from normal telescopes.