The term night sky refers to the sky as seen at night. The term is usually associated with astronomy, with reference to views of celestial bodies such as stars, the Moon, and planets that become visible on a clear night after the Sun has set. Natural light sources in a night sky include moonlight, starlight, and airglow, depending on location and timing. Weather phenomenon such nighttime thunderstorms can dominate the sky, and transient events such as a great comet.
The night sky and studies of it have a historical place in both ancient and modern cultures. In the past, for instance, farmers have used the state of the night sky as a calendar to determine when to plant crops. Many cultures have drawn constellations between stars in the sky, using them in association with legends and mythology about their deities.
Otherwise, Astrology is generally based on the belief that relationships between heavenly bodies influence or convey information about events on Earth. The scientific study of the night sky and bodies observed within it, meanwhile, takes place in the science of astronomy.
The visibility of celestial objects in the night sky is affected by light pollution. The presence of the Moon in the night sky has historically hindered astronomical observation by increasing the amount of ambient lighting. With the advent of artificial light sources, however, light pollution has been a growing problem for viewing the night sky. Special filters and modifications to light fixtures can help to alleviate this problem, but for the best seeing both professional and amateur optical astronomers seek viewing sites located far from major urban areas.
Shortly after sunset and before sunrise, artificial satellites often look like stars - similar in brightness and size, but different because they move relatively quickly; those that fly in near-earth orbit cross the sky in a couple of minutes. Some satellites (including space junk) appear to blink or have a periodic fluctuation in brightness because they are rotating.
Meteors (commonly known as shooting stars) streak across the sky very infrequently. During a meteor shower, they may average one a minute not at regular intervals, but otherwise their appearance is a random surprise. The occasional meteor will make a bright, fleeting streak across the sky, and they can be very bright in comparison to the night sky.