How does starlight travel through space?
Stars emit a constant and steady beam of light into the universe. This light travels along a path through the vacuum of space, where there is no matter to block or slow it down. Because space is a vacuum, the light moves in a straight line without any interference. It maintains its original intensity and direction for great distances until it encounters a planetary atmosphere like the one surrounding Earth.
What causes the light to bend?
When starlight reaches Earth, it must pass through the atmosphere. This region is a thick collection of air layers made of various gases that are constantly shifting and moving. These layers have different temperatures and densities, which cause the light to change direction as it passes through them. This process is known as refraction. As the light hits the moving gases, the beam is bent and knocked off its straight path multiple times before reaching the surface.
Why do stars look like they are moving?
The atmosphere moves so quickly that the refraction of the light happens in a fraction of a second. To an observer on the ground, this rapid bending makes the star appear to jump positions or change in brightness. This creates the perceived twinkle that people see from the surface of the planet. While the star itself is sitting still and shining steadily, the turbulent air makes the light seem to flicker before it reaches the eye of the viewer.