Constellation

A constellation is an area on the celestial sphere in which a group of visible stars forms a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. People have used constellations for thousands of years to tell stories, navigate, and understand the night sky. The first constellations were likely defined in prehistory, with different cultures creating their own groups of stars.

Twelve or thirteen ancient constellations belong to the zodiac, which follows the path of the Sun, Moon, and planets across the sky. These constellations have roots in Babylonian and Chaldean astronomy and later appeared in Greece. Today, the International Astronomical Union recognizes 88 official constellations, each with defined boundaries covering the entire sky. These constellations help scientists and stargazers identify and locate objects in the night sky.

Other patterns of stars, called asterisms, are not official constellations but are still useful for navigation. Examples include the teapot in Sagittarius and the Big Dipper in Ursa Major. Constellations connect us to ancient stories and help us explore the wonders above us.

Terminology

The word constellation comes from a Late Latin term meaning "set of stars." It entered the Middle English language in the 14th century. Ancient Greeks used a different word for these star patterns.

Today, there are officially 88 constellations, each with a Latin name, as decided by the International Astronomical Union. Some stars in a constellation appear close together in the sky, but they are often far apart in space. Over time, these star patterns slowly change as stars move.

Observation

Constellation positions change throughout the year because of Earth moving around the Sun. As Earth rotates, the sky seems to spin, with stars moving in circles around the north and south pole stars.

The Milky Way passes through many constellations, such as Cygnus, Cassiopeia, Orion, Puppis, and Vela. In the northern sky, Polaris, also called the North Star, helps point toward the north. In the southern sky, Sigma Octantis is close to the south pole but is hard to see.

History of the early constellations

Main articles: Old Babylonian astronomy, Egyptian astronomy, Ancient Greek astronomy, Chinese constellations, Chinese astronomy

People have been grouping stars into patterns, called constellations, for thousands of years. These patterns often matched animals, objects, or stories important to a culture.

The earliest proof of people using constellations comes from stone writings in Mesopotamia around 3000 BC. These early patterns influenced later Greek constellations. In ancient Babylon, detailed lists of stars and constellations were made during the Middle Bronze Age. The Greeks later adopted many Babylonian constellations.

Ancient China also developed its own system of constellations, recorded on special bones from the Shang dynasty and later organized during the Han period. These Chinese constellations were quite different but sometimes shared similarities with Babylonian ones.

Early modern astronomy

Most northern constellations have names from ancient Greek legends. These names have been used for a very long time, and we know about them from old star charts, like one shown on a statue called the Farnese Atlas. Southern constellations were created much later, mostly when sailors needed to navigate using the stars.

In 1603, a book called Uranometria by Johann Bayer gave each star in a constellation a Greek or Latin letter. This helped organize the stars into groups. Later, in 1922, astronomers agreed on 88 constellations that we still use today. These include both old Greek names and newer ones made for the southern sky.

Dark cloud constellations

Further information: Great Rift (astronomy) and Molecular cloud § List of molecular cloud complexes

Some cultures saw shapes in dark patches of the night sky. For example, the Inca people saw animals in these dark areas and linked them to seasonal rains. In Australian Aboriginal astronomy, one famous dark shape is called the "emu in the sky." Its head is formed by the Coalsack, a dark area in the sky.

List of dark cloud constellations

• Great Rift (astronomy)
  • Cygnus Rift
  • Serpens–Aquila Rift
  • Dark Horse (astronomy)
  • Rho Ophiuchi cloud complex
  • Emu in the sky