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Late Discoveries
It's sometimes interesting how we miss these small rocks until after closest approach. This appears to happen rather often. Take 2021 NU3 as an example, discovered just couple days ago, 1+ days after its close approach which occurred on July 8, 7:17UT (my location). The small (25') rock came in from the sun-ward side and directly over the north pole unseen at magnitude 15.7. It then continued outside our orbit and finally crossed the ecliptic a day later (9 July 3UT) at magnitude 17.6ish. At this point I think observations may have begun. It was actually a magnitude fainter when closest due to phase angle. At this point the orbit is still uncertain. Crazy stuff as sun-ward approaching rocks will surprise us.

Some useful tools for getting info on rocks your interested in can be found at

And there, you can get a geocentric flyby diagram if you don't have software to do detailed solar system simulations.
Like the Chelyabinsk object? That came from the sunward side and caused a bit of an issue when it hit.
Spotting these things after close approach is a fairly common occurrence, unfortunately. Anything coming from the sunward direction is naturally hard to spot. It usually misses & we can spot it, or it will never pass us again. If an asteroid explodes over the Pacific, does it make a sound? Sure does & sometimes our detectors can hear it.

The amazing ones are those that skip off the atmosphere & continue on.

Thanks for the web link BMD. It doesn't like the way I have MS Edge set up.

Phil S.

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