Science How is it possible that scientists estimate that the universe is 13.7 billion years old, but more than 90 billion light-years across?
Exotic Objects When scientists talk about the rotation of a black hole, what are they referring to? If we can’t see a black hole, how can we tell if it rotates?
Science I read that ultraviolet light is the cause of HII regions, but this light is invisible. So why are these objects the color red?
