Whoops! Forget my gibberish from the previous post!
2008 BT18 distance from Earth was over 10 LD’s, so being very conservative, let’s put it at 3,780,000kms. Now if I can dredge up some very, very rusty trigonometry, I think that:
Tan ⊖ = Opposite/Adjacent.
Assume a peak to peak separation of 600 metres. Half this is 300 metres.
So we get Tan ⊖ = 0.3/3,780,000 = 0.000000079 degrees
Which is a meagre 0.00028 arcsecs, much, much smaller than my estimate of 4 arcsecs.
Oh well, back to kindergarten for me!
Cheers
Dennis