Celestial bodies are always an object of awe and mesmerisation. The stars and sky are an endless span of mystery that many geniuses together unravel. Let’s delve deeper into this interesting subject and learn more about constellations and asterisms.
What are constellations and asterisms?
The International Astronomical Union has recognised 88-star patterns as constellations. Technically, the constellations are divisions of the sky that make it easier to locate celestial objects.
At first, constellations were determined by the shapes that their star patterns created, but as astronomical discoveries accelerated in the early 20th century, astronomers believed that having a standard set of boundaries would be beneficial. One of those standard norms was to help name new variable stars, which shine intermittently rather than continuously. It is crucial to agree on where one constellation ends and another begins because such stars are named for the constellation in which they are located.
In the Délimitation Scientifique Des Constellations, published on behalf of IAU Commission 3, Eugène Delporte first enumerated the 88 “modern” constellations.
An asterism is a pattern or collection of stars that are observed in the sky. Asterisms are a broader concept than the 88 officially recognised constellations because they can represent any recognised pattern or collection of stars.
What is the difference between constellations and asterisms?
So, how are constellations and asterisms different?
Asterisms have served as the basis for the 88 categorised constellations. Although constellations are based on asterisms, they entirely divide the sky and all of its celestial objects into regions around their centre asterisms, unlike asterisms. The Big Dipper, for instance, is an asterism made up of the seven brightest stars in the constellation Ursa Major. Another example is the Southern Cross asterism, which is located in the constellation Crux.
Source: EarthSky-org | The Big Dipper is an asterism made up of the seven brightest stars in the constellation Ursa Major.
Asterisms can range in complexity from modest gatherings of a few stars spanning small areas of the sky to more complicated collections of many stars. Even while the stars may be fainter or even invisible to the human eye, they are typically all of the similar brightness to one another. For those who are curious and getting acquainted with the night sky, the larger, brighter asterisms are helpful.
Asterisms are made up of patterns of stars that are not necessarily the consequence of any physical association between the stars but rather are the outcome of the observers’ unique points of view—the major difference between constellations and asterisms.
Source: Wikipedia | The stars of Orion’s Belt are all members of the Orion association
The stars of Orion’s Belt, for instance, are all members of the Orion association, and five of the stars comprising the Big Dipper are part of the Ursa Major Moving Group, whereas the Summer Triangle is solely an observational group of stars that is not physically related. Physical associations like the Hyades or Pleiades can be independent asterisms and components of other asterisms.
Big Dipper – Ursa Major
Source: Star Name | Constellations and asterisms: Ursa Major
The enormous bear constellation, Ursa Major, is visible in the northern hemisphere. It is an expansive constellation, covering 1,280 square degrees. The third-largest constellation in the night sky as a result.
Source: Pinterest |Constellations and asterisms: Bigger Dipper in Ursa Major
The Big Dipper comprises Ursa Major’s seven brightest stars. These stars outline the bear’s exaggerated tail and hindquarters, or they could represent the “handle” that forms the top of its head and neck. The constellation Ursa Minor, sometimes known as the Little Dipper, has a longer tail and hardly resembles a bear at all.
Ursa Major, to the north, has several asteroids. The bright stars Alkaid (Eta UMa), Mizar (Zeta UMa), Alioth (Epsilon UMa), Megrez (Delta UMa), Phecda (Gamma UMa), Dubhe (Alpha UMa), and Merak combine to form the most well-known of these, the Big Dipper (Beta UMa).
Southern Cross – Crux Constellation
Out of the 88 constellations, it is the smallest. Crux is one of the most well-known constellations in the southern hemisphere despite its small size. The Southern Cross, an asterism formed by its five brightest stars, makes it simple to identify. The constellation is linked to a variety of tales and is a central figure in numerous southern hemisphere myths.
Source: EarthSky.org | Crux is one of the most well-known constellations in the southern hemisphere despite its small size.
By name, the Southern Cross is an asterism, but today, the entire region is known as the constellation Crux. The brightest stars in the constellation Crux, including Acrux (Alpha Crucis), Mimosa (Beta Crucis), Gacrux (Gamma Crucis), Imai (Delta Cruis), and Ginan, make up the Southern Cross (Epsilon Crucis). The smallest of the five stars, Ginan, is not often seen in representations of asterism. When Bayer constructed Crux in Uranometria (1603) using stars in Centaurus’ hind legs, he reduced Centaurus’ size and declared it to be an asterism.
Like its southern neighbours, the Diamond Cross and the False Cross, for which it is occasionally mistaken, the Southern Cross does not resemble a cross. It resembles a diamond more. It has two first-magnitude stars (Acrux and Mimosa) at its vertices, making it appear brighter and smaller than the other two asterisms.
Fish Hook – Scorpion
Source: ThoughtsCo | Constellations and asterisms: Fish Hook in Scorpion
The scorpion-shaped constellation Scorpius can be found in the southern hemisphere of the night sky. Although it is low in the sky and best visible from the southern hemisphere or the southern United States, it can be seen in the summer from the northern hemisphere. At latitudes between 40 and -90 degrees, it can be seen.
Between Libra to the west and Sagittarius to the east is where it is located. If the chart’s lines from Antares to Beta Scorpii and Pi Scorpii are swapped out for a line from Beta to Delta Scorpii to Pi, a giant capped “J” will form, making the image even more clear.
The asterism known as the Fish Hook is what gives the constellation Scorpius its distinctive appearance. The native Hawaiian term for Scorpius is The Fish Hook. The Fish Hook is located between the Teapot and the Scorpion’s claws and is outlined by a sloping line of stars that runs from Antares at heart to Shaula and Lesath at the stinger.
Xamidimura (Mu1 Scorpii), Pipirima (Mu2 Scorpii), Zeta1 and Zeta2 Scorpii, Eta Scorpii, Sargas (Theta Scorpii), Paikauhale (Tau Scorpii), Iota Scorpii, Antares (Alpha Scorpii), Kappa Scorpii, Shaula (Lambda Scorpii), and Lesath (Upsilon Scorpii) are the stars that make up the asterism.
Kite – Boötes
Source: Universe Today | Constellations and asterisms: Kite in Boötes
Boötes is occasionally referred to as the Ice Cream Cone. One of the brightest stars in the night sky, Arcturus, may be found in the northern hemisphere constellation Boötes. The best time to observe Boötes is in the spring, rising in the northeast after dusk. Looking down the handle of the Big Dipper away from its spout, arcing to the bright orange star Arcturus, creating the base of the constellation Boötes, which to some observers resembles a kite, i.e. Kite asterism
The Kite, which may be seen on a clear night between the handle of the Big Dipper and the crown-like pattern of Corona Borealis, is a little fainter than these two objects. A nickname for Cassiopeia is the shape of its stars, which resemble a W.
It also includes the stars Izar (Epsilon Boötis), Princeps (Delta Boötis), Nekkar (Beta Boötis), Seginus (Gamma Boötis), and Rho Boötis. Izar and Rho Boötis are sometimes left out of the pattern, while Zeta, Eta, Tau, and Upsilon Boötis are sometimes added to give the celestial Kite a tether and tail.
Y of Virgo – Virgo
Source: Space | Constellations and asterisms: Y of Virgo in Virgo
At 1294 square degrees, Virgo is the second-largest constellation in the sky. One of the fifteen equatorial constellations is it. It can be visible from latitudes between +80° and -80° in the southern hemisphere’s third quadrant (SQ3).
The most noticeable aspect of Virgo is its Y. The asterism, Y of Virgo, is located in the western region. The brightest star in Virgo, Spica, forms the letter Y alongside Porrima, Minelauva, Vindemiatrix, Epsilon Vir, Zaniah, and Zavijava (Beta Vir). Just above the asterism, midway between Vindemiatrix and Denebola, is the Virgo Cluster of galaxies.
Why constellations are important?
Despite the differences between constellations and asterisms, they find similar use cases in the practical world. Let’s find out why constellations are important.
- Constellations were probably first used for religious purposes. Numerous tribes thought that their God would reveal tales through the positions of the stars. So it made sense to name the patterns in the sky, recognise them, and make up stories about them. The Greeks gave us the names of constellations based on their mythological figures of fame.
- Agriculture was a more useful application for constellations. Before accurate calendars, people had no other way to know when to plant or harvest but by looking at the stars. The constellations made it simple to recall the star patterns.
- The constellations were useful for navigation as well. Once you have located Ursa Minor, finding Polaris (The North Star) is quite simple (Little Dipper constellation). Polaris’ apparent height in the night sky can be used to determine one’s latitude. This made it possible for ships to sail around the world. It made it possible for the discovery of countries, cultures, and civilisations.
- Constellations determine the names of stars. Astronomers enjoy presenting their discoveries to other researchers at conferences. Additionally, people frequently wish to share the stars or objects they may be observing with someone. The other person is unlikely to immediately understand the star’s location in the sky if they only provide the coordinates (numbers).
- Asterisms are crucial for celestial navigation and are used in observational astronomy as a point of reference for recognising stars and locating deep-sky objects.
Constellations and asterisms share overlapping boundaries of distinction. The difference between constellations and asterisms, if observed, can be demarcated. Both constellations and asterisms are crucial in astronomy and real-world applications.
Whether you are a seasoned veteran in the world of constellations and asterisms or someone looking to develop their knowledge, we hope this article helped answer some of the biggest questions such as ‘why constellations are important?’ and ‘how are constellations and asterisms different?’.