We picture a comet's tail trailing behind it like smoke. In fact, it always points away from the Sun, pushed by the solar wind and the pressure of sunlight. So when a comet heads away from the Sun, its tail leads the way. And it often has two: one of dust, one of electrically charged gas.
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.