When we look at the night sky, stars shine like small lights. Many stars seem to move a little. We say they twinkle.
Starlight travels from space to Earth. Before it reaches our eyes, the light passes through Earth’s atmosphere. The air is always moving a little.
Moving air changes the path of starlight in small ways. Because of this, a star may appear brighter, then darker. The star is not really turning on and off. We are seeing its light after it travels through moving air.