If you'd been an astronaut on the International Space Station last month, you might have often looked out the window and seen this: Earth's atmosphere, laid out as plain as day, like rainbow-colored layers of an onion.
From the top: First, there are the deep blues of the upper atmosphere, which is responsible for the blueness of our sky, as seen from the ground. Next is a lemon yellow slice of stratosphere, 30 miles (50 kilometers) above Earth's surface, which would be an arid place in person—few clouds are found at such heights.
Glowing pumpkin orange in this May 25 picture, which was released June 14, the troposphere holds nearly all of the water vapor above Earth. Variations in its color, such as the dark streaks at right, are caused by clouds or airborne particles. Wafting 4 to 12 miles (6 to 20 kilometers) above Earth's surface, the troposphere also holds 80 percent of the mass of our planet's atmosphere.
And somewhere, deep beneath it all, is the Indian Ocean.
(Learn more about Earth's atmosphere.)