Earth is covered with water today, but it did not begin with oceans. The young planet formed about 4.5 billion years ago in a hot, violent Solar System, and liquid water had to accumulate as Earth cooled. So, how did water come to Earth? Scientists think it was probably a combination of sources and processes. […]
How Did Water Come to Earth? The Story of Earth’s Oceans Read Post »
The Sun’s gravity pulls planets toward it, so why don’t they fall into the Sun? The simple answer is that planets are already moving forward through space. The Sun’s gravity continually pulls them inward and changes the direction of that motion, producing a curved path around the Sun. That curved path is an orbit. This
Why Do Planets Orbit the Sun? The Science Explained Simply Read Post »
What Happens If You Fall Into a Black Hole? Imagine falling toward a black hole. At first, nothing dramatic happens. As you get closer, however, gravity becomes stronger and spacetime becomes increasingly distorted. Light bends around the black hole, distant objects appear warped, and the difference in gravity between your head and feet begins to
What Happens If You Fall Into a Black Hole? Read Post »
Stars are not all alike. Some are small and relatively cool, while others are enormous, hot and short-lived. The stars we see today also contain elements such as carbon, oxygen and iron that were made by earlier generations of stars. The first stars formed under very different conditions. They appeared during the universe’s early history,
What Were the First Stars Like? How Different Were They From Today’s Stars? Read Post »
Before there were stars, the universe was a very different place. There were no galaxies shining across the sky, no planets orbiting suns, and no familiar starlight. The young universe was filled mainly with hydrogen and helium gas, along with dark matter and radiation. Over time, gravity pulled matter into denser regions, allowing some clouds
The First Stars: How Did They Form in the Early Universe? Read Post »
Cosmic Inflation: How the Early Universe Expanded in a Fraction of a Second A second after the Big Bang, the universe was already expanding, cooling, and filled with an extremely hot mixture of particles and radiation. But if we move further back into cosmic history, we encounter an even more extreme possibility: cosmic inflation. Inflation
Cosmic Inflation: How the Early Universe Expanded in a Fraction of a Second Read Post »
What Happened One Second After the Big Bang? Inside the Newborn Universe One second seems almost meaningless on a human timescale. But one second after the Big Bang, the universe was already undergoing enormous physical changes. It was expanding and cooling from an extraordinarily hot, dense state. The temperature was around 10 billion kelvin, or
What Happened One Second After the Big Bang? Inside the Newborn Universe Read Post »