Whenever explaining astronomical ideas to a "lay-person", it seems that the most difficult concept to get across is the scale of things in the universe. It's challenging to understand just how vast our universe is, that it takes light over four years to get from our sun to the nearest star, that it would take light 2.5 million years to get from our galaxy to Andromeda, the nearest large galaxy.
And yet, I sometimes feel like even astronomers don't fully comprehend the scale of what we look at through our telescopes. This image is the Astronomy Picture of the Day from yesterday. I'm used to seeing pictures of these nebulosities up close, as taken with large telescopes, but even looking at the night sky through a telescope doesn't really convey how far they extend. I had no idea that these nebulae took up such a large portion of the sky. It's a pity that most of this structure is much too faint to see with the naked eye (especially in a Toronto sky where even the luminous Orion Nebula looks unimpressively faint through a 10" telescope).