There can be several reasons why a light source may appear and then disappear. Here are a few possible explanations:
Obstruction: If an object or obstacle comes in between the light source and the observer, it can block the direct line of sight, causing the light source to appear as if it has disappeared. For example, if you are observing a distant light source, and something moves in front of it, such as a person or an opaque object, the light source will be temporarily obscured from your view.
Intermittent Source: Some light sources may be designed to emit light in a periodic or intermittent manner. For instance, certain types of warning lights or beacons may be programmed to flash at regular intervals. During the periods when the light is off, it may appear as if the light source has disappeared.
Power Failure: If a light source is connected to an electrical power supply, a power failure or interruption can cause the light source to turn off abruptly, leading to its apparent disappearance.
Atmospheric Conditions: In certain situations, atmospheric conditions like fog, mist, heavy rain, or dense cloud cover can scatter or absorb light, making a light source less visible or seemingly disappear. These conditions can significantly reduce the visibility of distant light sources.
Optical Effects: Optical phenomena such as mirages or refraction can alter the apparent position or visibility of a light source. For example, in certain conditions, such as when light passes through layers of air with varying temperatures, it can refract and create optical illusions, causing objects or light sources to appear displaced or disappear momentarily.
These are just a few examples of factors that can cause a light source to appear and then disappear. The specific cause would depend on the circumstances and conditions under which the observation is made.