When you look up at the sky and stars seemingly "randomly" appear, what you are experiencing is a visual phenomenon known as the "autokinetic effect." The autokinetic effect refers to the perceived movement of a stationary light source in a dark environment. It occurs because our visual system relies on relative motion and contrasts to perceive motion accurately.
Here's how it works: When you stare at a fixed point of light in the dark sky, your eyes involuntarily make small, rapid eye movements called microsaccades. These microsaccades cause the light source to appear as if it is moving. Additionally, our visual system tends to fill in gaps and make assumptions about visual stimuli in the absence of clear and consistent cues. This can create the illusion that the stars are flickering or moving.
Furthermore, the autokinetic effect can be influenced by other factors such as the adaptation of your eyes to darkness, fatigue, and the absence of visual references. When there are no nearby objects or landmarks to provide a frame of reference, it becomes more challenging for your brain to accurately perceive the motion or lack thereof.
It's worth noting that the autokinetic effect is not exclusive to stars but can occur with any stationary light source in a dark environment, such as distant streetlights or even small bright spots on a blank wall.
While the autokinetic effect can give the impression that stars are appearing and moving randomly, it is an illusion created by the intricacies of our visual system and the lack of visual cues. Stars themselves do not spontaneously appear or move, but rather, they are distant celestial objects that emit or reflect light, visible to us depending on various factors like atmospheric conditions and light pollution.