I am not American, so this might just be something in my country, but growing up everyone knew about the nuclear bombing of Hiroshima. However, when we began studying this in high school everyone was surprised to learn that a second bomb was dropped on Nagasaki. Many times I've encountered people who have heard about Hiroshima but not Nagasaki.
Were they reported on differently at the time? Is there some historical reason for one being more infamous than the other (other than one being the first)?