According to the leading theory, a spiral galaxy's arms aren't fixed structures rotating as one, but density waves: zones where stars and gas slow down and bunch up, like cars in a traffic jam. Stars drift in, then out again. The arms shine mostly because compressed gas there gives birth to young, brilliant stars.
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.