On a clear, dark night, our eyes can see thousands of stars in the sky in places without light pollution. They always seem to twinkle, or change their brightness, all the time, but in reality it's the movement of air (sometimes called turbulence) in the atmosphere of Earth causes the starlight to get slightly bent as it travels from the distant star through the atmosphere down to us on the ground, producing a twinkling effect. You'll notice that stars closer to the horizon will appear to twinkle more than other stars. This is because there is a lot more atmosphere between you and a star near the horizon than between you and a star higher in the sky. Continue reading for more.