Hi Bill,

I know exactly what you mean about 2008 TC3. We have a visualization of it installed in our planetarium, based on XYZ data from the NASA Horizons ephemeris website. We sit up above the Earth and watch the point of light remain stationary for quite a long time (moving towards us), then start showing apparent motion and then CRASH into the Sudan. But there was only 24 hours of advance warning for TC3, and I know the story was still developing during that time. Did you actually see the change in apparent motion soon enough that it clued you in to what was happening in real time?

Andy

--- In find_orb@yahoogroups.com, Bill Gray <pluto@...> wrote:
>
> Hi Glen,
>
> > As I understand it, the authors of that paper used NOVAS to calculate
> > the orbit. Couldn't they just as well have used Find_Orb?
>
> Yes. Very shortly after the impact, I got an inquiry about this
> from someone hoping the object might be found on recent survey images.
> That resulted in my posting this pseudo-MPEC, with a (G96)-centric
> ephemeris to see if any of the southwestern US folks might have
> gotten the object on the way in :
>
> http://www.projectpluto.com/temp/chelyab.htm
>
> You'll notice that this was computed on the day of the impact, and
> was intended just to get a rough idea (enough to say, "Sorry, no,
> there aren't going to be any precovery images.") I'm sure Esko
> Lyytinen and/or Rob Matson and/or somebody else got more and better
> data after that. But even the very approximate data were enough to
> make it clear: this object came from too low an elongation to be
> spotted on its way in.
>
> I will not be surprised if it's a long time before another case
> occurs of an impactor observed before impact. It _has_ happened
> once (2008 TC3), and I keep an eye on NEOCP for objects that might
> do this. (The key sign is that the ephemerides show virtually no
> motion, then suddenly show _lots_ of motion. That was what clued
> me in for 2008 TC3.) But I'm not really optimistic.
>
> -- Bill
>