FORMING DAY AND NIGHT
Long, long ago—about 4.6 billion years in the past—there was no day, no night, and no Earth. There was only a massive, swirling cloud of gas and stardust drifting through the freezing emptiness of space. Slowly, gravity began to pull this cosmic dust together. At the very center of this swirling cloud, material packed so tightly that it ignited into a raging ball of nuclear fire: our Sun. Further out from the newborn Sun, leftover rocks and dust collided and melted together, eventually forming a vibrant, blue-and-green jewel of a planet. Earth was born. But it was not born to stand still. The Birth of the Great Dance As Earth formed from that swirling cosmic dust, it kept the momentum of its birth. It began to spin like a colossal top suspended in a frictionless room. Because the Sun is a fixed, brilliant spotlight in the center of the solar system, it could only ever shine its light on one side of the spinning Earth at a time. This cosmic geometry created two distinct realms that woul...
