A student is taking an astronomy class in college.
One day, the professor lectures about the solar system and mentions the sun will explode and kill all life on Earth in about 5 billion years.
After class, the student nervously approaches the professor and asks, “Professor, excuse me, but did you say the sun is going to explode and destroy the Earth in five million years?”
The professor shakes his head and says, “No, no. I said five *billion* years.”
The student clutches his chest, lets out a massive sigh of relief, and says, “Oh, thank goodness. You really had me worried there for a minute!”