Funnily enough, it was actually while I was sat in church with my family when I was younger (I've since lapsed profoundly and comprehensively, of course) that my mind first began to wander to and wrestle with such concepts.
Reading Clarke and imagining being in a spaceship in orbit around Jupiter and seeing it dominate the exterior view.
Trying to imagine a ball of fire as big as the Sun.
Seeing the solar giants in images like these: http://www.rense.com/general72/size.htm or videos like this: http://sciencehack.com/videos/view/_WEL117xXpw
Antares is huge, lol. Well, not lol, more ... scared.
Hubble Deep Field.
It's awesome in the literal sense of awesome.