What is a Constellation? – Everything You Need To Know

Constellations are groupings of stars in the form of configurations of objects in the sky. Astronomers study the constellations among other celestial objects such as sun, moon, planets and other phenomena in space.

In the past travelers used constellations to help find their way around cities. The constellation patterns were also used to identify and measure the seasons.

Some constellation shapes might appear more obvious than others. The smaller parts of constellations are called asterisms and they are also named based on their shapes. The constellations take up larger areas and are much bigger than asterisms. For example, the Big Dipper, Little Dipper and Southern Cross are asterisms, not constellations. They belong to the constellation Ursa Minor, the Little Bear.

While the constellations may appear as if jumbled close together, they are in reality distributed in space in three dimensions. When we look at the stars from naked eye, we are looking at them from very far away, so they appear as a cluster when in reality they are all located at different distances from the Earth. Hence, today, when astronomers or scientists talk about constellations, they refer to the stars that lie within the defined boundaries of the constellation.

One of the constellations Orion contains some of the biggest stars including Bellatrix, Meissa, Alnilam, and others. Orion stars lie at distances ranging from 243 to 1360 light years! Galaxies are even farther! The closest known galaxy to us is the Canis Major Dwarf Galaxy, and it lies at 236,000,000,000,000,000 km (25,000 light years) from the Sun.

Where Did Constellations Come From?

In earlier times, various stars and constellations have received their names connoting mythological animals and peoples or religious beliefs.

There are varying stories regarding the origins of constellations. Various cultures used them to express and relate their religious beliefs or mythology. The earliest known constellations may date back to Greek or Roman cultures where they related the shapes of stars to gods and goddesses. Aratus in his book Phenomena and Ptolemy in Almagest list the names and origins of the stars, their motion, and other celestial phenomena.

The Almagest contains a star catalogue, which includes 48 constellations. Some of which include Ursa Minor, Ursa Major, Hercules, Aquila, Taurus, Cassiopeia, and others. Ptolemy only observed one part of the sky and after the 15th century, with more explorations and discoveries, the southernmost parts of the sky became known.

The belief in constellations was not just limited to one area of the world, rather, the ancient Chinese, Middle Easterns and Native Americans also observed and followed celestial phenomena in their cultures.

Modern constellations were internationally recognized when in 1928, the International Astronomical Union (IAU) adopted a list of 88 constellations that cover the entire celestial space.

The 88 constellations are broken down into 42 animals, 29 inanimate objects and 17 humans or mythological characters. Some of these include Greek Princess (Andromeda), Ram (Aries), Chisel (Caelum), and others.

How Did the Constellations Get Their Names?

In older times, people gave the stars names as they wished. For example, Andromeda, one of the constellations of Greek mythology, was named after Andromeda, the daughter of Cassiopeia and Cepheus.

Stars that indicate an Arabic origin begin with “Al” which indicates article “the” in English. For example: Algol (The Demon), Albali (The Swallower), and Algebar (The Giant) are arabic star names.

Sirius (dog star) discovered in 1862 and Vega in 1850 are some of the brightest stars in the galaxy. They were already widely known to the astronomers. Most stars however, were later named in various books and articles.

Today, however, stars are named according to their characteristics and their placement in the celestial sphere. With telescopes having become common, more stars were revealed to the scientists as they began assigning names to them.

Most recently, professional astronomers do not use stars names, rather they refer to stars by designations - combination of letters and numbers (alphanumerical). For example Fomalhaut is HD 216956 and Vega is GC 25466.

What are Zodiac Constellations?

Zodiac constellations are a list of 13 constellations through which the sun appears to travel during the year. Although considered the 13th or forgotten constellation of the Zodiac, Ophiuchus is also part of the list. The sun passes in front of Ophiuchus from about November 30 to December 18, however, it is not considered a Zodiac sign, rather a constellation. This is why astrologers only use 12 of these constellations to make predictions.

The zodiac use dates back to the Roman era and is based on concepts taken from Hellenistic astronomy from Babylonian astronomy. The zodiac construction is also mentioned in Ptolemy's Almagest.