Asteroid 2012 TC4 is a small roughly 20~30 meter asteroid that was originally discovered in 2012 and only observed over a week of time before it was too far from earth and too dim to detect. That resulted in a highly uncertain orbit determination, but predicted a return in October 2017 somewhere between the earth and moon. Until it was recovered in late July, the predicted orbit had an uncertainty that allowed for a close approach of anywhere from about 270,000 km to 6,800 km ( [link to cneos.jpl.nasa.gov (secure)] ).
In late July, just a couple weeks after that NASA article was published, the asteroid was re-detected as it approached close enough for the largest telescopes to track and locate it. The uncertainty in the orbit quickly dropped since time between observations is critical in reducing uncertainty. It is currently approaching earth for a close pass which is now known to be about 50,200 km away from the center of earth at its closest point, with an uncertainty only a few km wide.
Tonight at 8:00 pm eastern, midnight universal time, I’ll be tracking the asteroid during its approach using custom software that I’ve written to track fast moving objects telescopically, and I’ll be webcasting the images right here:
Clear sky clock calls for clear skies tonight in my area, but some forecasts do call for a slight chance of rain this afternoon persisting into the early evening along with partly cloudy conditions. The asteroid will set at about midnight at my location, shortly before closest approach, so the weather does need to clear well before then to have any chance of seeing it. I’m aiming for an 8pm eastern start time, but that is optimistic about the weather. If needed, I may delay the start time to ensure that my equipment does not get any rain on it. HaTTiP