The sky is the vast expanse that stretches above us when we look up from Earth. During the day, it appears as a beautiful blue dome filled with clouds, the sun, and sometimes the moon. At night, it transforms into a dark canvas dotted with countless stars and planets.
What we call the sky is actually Earth's atmosphere, made up of several distinct layers of gases. The troposphere is closest to Earth where weather occurs. Above it is the stratosphere containing the ozone layer. The mesosphere and thermosphere extend even higher, gradually fading into space.
The sky appears blue because of Rayleigh scattering. When sunlight enters Earth's atmosphere, it collides with tiny gas molecules. Blue light has a shorter wavelength and gets scattered in all directions much more than other colors. This scattered blue light is what we see when we look up at the sky during the day.
The sky changes color throughout the day because sunlight travels different distances through the atmosphere. At noon, sunlight takes a short path through the atmosphere, so we see blue sky. During sunrise and sunset, sunlight travels a much longer path, scattering away most blue light and leaving warm colors like orange and red.