Why Do Stars Blink or Twinkle?
Stars blink or twinkle when we observe them (from the surface of the earth) because we are viewing them through different layers of turbulent (swirling) air and temperatures in the Earth’s atmosphere (the mass of air surrounding the Earth). This therefore means that the Earth’s atmosphere is made up of several “layers” of moving air, each having different temperature and density.
When light from a star (traveling millions of miles) pass through these layers of the Earth’s atmosphere, it is constantly bent (refracted) by each layer of temperature and moving air several times in random directions. This random refraction distorts the image of the star slightly in brightness and position making it look as if it is moving and winking. Thus, this distorted image of the star that we are seeing in the sky causes our eyes to interpret this as a twinkling (blinking) star.
It is also important to note that in outer space stars do not twinkle because there is no atmosphere. So, strictly speaking, stars themselves do not twinkle but appear to do so through the Earth’s atmosphere. While some stars do physically change in brightness over time, they typically do so on long timescales — amateur astronomers monitor these changes sometimes over hours, but more often over days, weeks, or years. These variable stars are well studied and often signal complex physical changes happening to the stars in question.
The more rapid changes of scintillation, on the other hand, come about long after the light has left the star. Light waves traveling through Earth’s atmosphere diffract as they pass through pockets of air at different temperatures. Because the light waves come from a single point, this effect can make the star’s brightness and/or position appear to change.