Night sky

The night sky is the nighttime view of celestial objects like stars, planets, and the Moon. We can see these between sunset and sunrise, when the Sun is below the horizon. It is a beautiful sight that has fascinated people for thousands of years.

Natural lights in the night sky include moonlight, starlight, and airglow. Aurorae sometimes light up the sky near the polar circles.

The night sky has been important to many cultures and people throughout history. Ancient farmers used it as a calendar to decide when to plant crops. Many cultures made constellations by connecting stars and told legends and mythology about their deities. Today, scientists use observational astronomy to study the universe.

Unfortunately, light pollution from cities makes it harder to see the night sky clearly. Bright lights create skyglow that hides faint stars. Many amateur astronomers travel to dark places to see the stars and planets better.

Brightness

Main article: Sky brightness

Even when there is no moonlight or city lights, the night sky is not completely dark. This is because of natural light sources such as airglow and the faint scattering of sunlight and starlight. The brightness of the sky changes throughout the day. During the day, sunlight scattered in the atmosphere makes the sky bright. After sunset, the sky gradually darkens through periods called civil, nautical, and astronomical twilight, until it reaches its darkest point when the Sun is far below the horizon.

Visual presentation

The stars in the night sky look like tiny points of light. Long ago, people thought all stars were the same distance from Earth. Stars can be blue or red, but most look white.

To see the most stars, go to a dark place far from city lights. Our eyes need time to adjust to the dark. A red flashlight can help us see star maps without hurting our night vision.

Constellations

Star maps show patterns in the stars called constellations. Different cultures see different pictures in these patterns. Well-known constellations are Orion and the Big Dipper, which can help find the north star, Polaris.

Planets

Planets move slowly across the sky and look like bright stars. They shine because the Sun's light reflects off them. Venus is often the brightest object in the night sky and can be seen near sunrise or sunset. Other planets like Mercury, Mars, Jupiter, and Saturn can also be seen without special equipment.

The Moon

The Moon looks like a grey circle with craters and changes shape over about a month. It is bright enough to see even during the daytime. Near sunrise or sunset, the Moon can look orange or red because of Earth’s shadow.

Comets

Comets are rare visitors to the night sky. When they appear, they often have tails that point away from the Sun. A very bright comet, called a great comet, appears about once every ten years.

Clouds

Clouds can hide stars and planets. Thin clouds might make a colorful ring around the Moon, while thicker clouds hide everything completely.

Other objects

On very dark nights, you might see the Milky Way, our galaxy, as a fuzzy band of light. Sometimes satellites move across the sky and look like stars, but they move quickly. Meteors, or shooting stars, sometimes flash across the sky, especially during meteor showers.

Sky map

Main article: Starchart

The night sky has many stars. Special maps called starcharts help us find them. There are maps for the Southern Hemisphere and the Northern Hemisphere. These maps show the brightest stars and groups of stars called asterisms. They also show important parts of our galaxy, like dark areas and groups of stars. Some maps even show groups of galaxies in the night sky.

Future and past

Main articles: Fixed star § "Fixed stars" not fixed, Variable star, and Astronomical chronology

The night sky is always changing. Stars move slowly across the sky and can get brighter or dimmer over time.

In the very far future, our Milky Way galaxy will slowly merge with the nearby Andromeda Galaxy, creating one large galaxy. This will change how the night sky looks from Earth.