In 1974, Hawking bet physicist Kip Thorne that Cygnus X-1, a powerful X-ray source, was not a black hole. He called it an insurance policy: if black holes didn't exist, his life's work would be wasted, but at least he'd win the bet. In 1990, faced with mounting evidence, he conceded and paid Thorne with a one-year magazine subscription.
A large share of Earth's water molecules formed in the interstellar cloud that existed before the Sun was even born, more than 4.6 billion years ago. You are literally drinking a cosmic fossil.
By day, the Martian sky looks butterscotch because of fine dust hanging in the air. But at dusk, those same grains scatter blue light forward, creating a bluish glow around the Sun. Rovers have photographed these blue sunsets: the exact reverse of what we see on Earth.