Asteroid 2000 EM26 passing by earth to say 'Hi' (live video)

No, it turned out the object had transformed into an ultra dense rectangular black obelisk and then some NSA warning flashed on the screen and then it was just random Chelyabinsk footage.

So where does “an arse the size of Belgium” fit in?

By ‘fit in’, I mean it’s relevance… I realise that the phrasing could be misconstrued

That is a bilateral unit - one meaning is the area covered by the sitting arse and the other the volume of that same arse when standing.