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Sunday, November 6, 2011

Horseshoes and hand-grenades

Tuesday, around 3:28pm pst, asteroid 2005 YU 55 is going to pass within the moon's orbit of us. A quarter of a mile (400 meters) in diameter, this is the largest asteroid to pass within the moon's orbit that we have ever known about (certainly lots of bigger ones have come even closer, we were just blissfully unaware of them). We have NEO's every single day, but this is one seriously big son of an accretion disk. If it were to actually hit the earth (don't worry, it won't, at least not in our lifetimes) the equivalent kinetic force would be greater than if every single nuclear warhead on every single missile on every single ballistic missile submarine in every single navy -- US, UK, France, Russia, China and India -- were to successfully detonate at the same location at the same time. Really. Which is still miniscule compared the the K/T asteroid which wiped out the dinosaurs (which was some 30 times larger), but, still, this is a big effing rock coming by tomorrow.

This will provide astronomers a very close view of a pretty large asteroid that we won't have to leave home to see, which is valuable. Nearly as useful, it serves as a not-so-subtle reminder that we really need to have the capability to intercept and deflect such objects all the time, not just whenever congress decides that it might be fun to budget for such things.

It will be visible from most of North America Tuesday evening, tracking from Aquila through Pegasus in about 10 hours time, but at a maximum visual magnitude of 11.2 it will require at least a 6" reflector telescope to see. Here's the track, from Sky and Telescope magazine:

Below is a very well done graphic from, with lots more information about this and other large NEOs --

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