David Witteveen recently posted this image on his website, which puts the universe into perspective, on just how big it really is. This kind of mind-blowing perspective is what got me into writing science fiction in the first place.
Wikipedia has an interesting article on how big the universe is here. The observable universe is 13.7 billion years old and 93 billion light years across, because space expands faster than light. The observable universe has an estimated 7 x 10 to the power of 21 stars (70 sextillion) , i.e. what we can see due to the speed of light limit from the Big Bang. How big the universe actually is is anyone's guess.