Measuring the speeds of galaxies in the Coma Cluster, astronomer Fritz Zwicky found they were moving far too fast: the visible matter could not hold them together, and the cluster should be flying apart. He proposed "dunkle Materie", a dark, invisible matter. His idea stayed on the fringes for nearly forty years before it was finally taken seriously.
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.