The Bullet Cluster is made of two galaxy clusters that passed right through each other. Their hot gas, slowed by the impact, got stuck in the middle. But by measuring how the whole system bends the light of background galaxies, astronomers showed in 2006 that most of the mass had carried on. Invisible, frictionless matter: a perfect portrait of dark matter.
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.