When you stare in amazement at something, you gawk at it. You might stand frozen in one position with your mouth and eyes wide open and gawk when you see a famous movie star on the street.
The verb gawk was first recorded in American English in 1785. It may have evolved from the word gaw, which came from the Middle English word gowen, meaning "to stare." When you gawk at something, you get completely absorbed in what you're looking at. It's usually not considered polite behavior to gawk at another person, especially if it's someone you find attractive. After all, staring is rude.