autokinetic effect
The autokinetic effect is an apparent motion: a stationary point of light, viewed for a long time in darkness without a reference point, appears to the observer to waver and shift. It is a common explanation for some nighttime UFO/UAP sightings.
The autokinetic effect (also known as the autokinetic illusion) is a perceptual phenomenon in which a point of light that is actually stationary, viewed in a dark environment without a reference point, appears to move. The light then seems to waver, drift or suddenly jump, even though its source does not move.
##How it arises
The phenomenon was first observed by Alexander von Humboldt in 1799 while looking at stars. It was named by Hermann Aubert in 1887, and from the 1930s it was studied experimentally in detail, by Muzafer Sherif among others. The exact mechanism is still debated today. According to the most common explanation, it is caused by small, involuntary movements of the eye, because without a fixed background the brain cannot decide what is moving: the light or the eye. The longer and the narrower the field of view with which we look at the light, the stronger the effect can be. The direction and extent of the apparent motion vary from person to person, and suggestion can also influence it. Sherif's experiments showed that if someone else mentions movement, the others may see similar movement too.
##Role in UFO/UAP sightings
According to a number of official investigations and analysts, for some points of light seen in the night sky (for example a star, a planet or a distant light source), the motion described by observers can be explained by the autokinetic effect. Such reports should therefore be treated with caution, especially if the observer had no fixed reference point, such as the horizon, trees or buildings.
The effect does, however, have its limits. The apparent motion is usually small in extent, a wavering of a few degrees, so on its own it does not explain a light that quickly travels a long path across the sky. Consistent descriptions from several independent witnesses or instrument data may also point toward a different explanation. The autokinetic effect is therefore a possible explanation, but on its own it does not settle the nature of a specific sighting.