Rosetta's comet, with ISS superimposed for size perspective.

You've probably seen spectacular images like this of comet 67P, taken by the Rosetta spacecraft. Science texts will tell you it's "3.5×4 km (2.2×2.5 mi)" in size, but that's dryly intellectual.

Humans are visual creatures, and with nothing in the image to provide visual scale, there's no "gut feel" for the size of the thing.

So, Will Gater (@willgater) posted the next image: "For a bit of fun I dropped a scaled ISS into that great new @ESA_Rosetta image of Comet #67P: pic.twitter.com/m5EwM5MP9f"

In case that's hard to see, I added a circle:

And then, the comet's size snaps into focus.

Rosetta's not a particularly large comet, either.

So now, statements like "The dinosaurs may have been wiped out by a cometary impact..." make a lot more sense, eh?