Sunsets are often depicted in paintings with majestic, beams streaming up radially into the sky from the already set Sun. Exaggerated as the artist may make them appear/sunbeams can often be seen in clear skies 10 to 15 minutes after sunset (or before sunrise). This phenomenon is called crepuscular radiation (from the Latin word crepusculum, meaning "twilight").
Crepuscular rays are caused by a cloud, below the horizon partially. blocking the Sun. The shafts of sunlight that get past the cloud illuminate dust particles in the air above the horizon, creating spectacular rays that occasionally reach to the opposite point in the sky. As the cloud moves and the Sun's angle changes, the rays too, shift across the sky. The phenomenon may last for several minutes.