How our visual systems distinguish patterns in the night sky

(ORDO NEWS) — There are hundreds of billions of stars in our galaxy, but only about 5,000 are visible to the naked eye. Under ideal conditions and away from city lights, about half of them can be seen on any given night.

Since humans are pattern-seeking animals, peoples of many cultures and eras have imagined that certain stars form distinct shapes and patterns that have had special meaning in their cultural traditions.

Modern astronomy has shown that some of these patterns are real star clusters – brother stars born in the same stellar nursery. Others are simply visible groups of stars that have randomly clustered together along our line of sight.

Today we officially recognize 88 constellations as defined by the International Astronomical Union. These formalized groupings, whose names were taken mainly from the Middle Eastern, Greek and Roman cultures, help scientists and amateur astronomers divide the celestial sphere into recognizable pieces in order to better determine the location of relatively near and far space objects.

In addition to the modern recognized constellations, various cultures throughout history have informally grouped stars into patterns called asterisms. Evidence suggests that this practice dates back at least 17,000 years ago, when Paleolithic people in what is now southern France painted images of what may have been the Pleiades and Orion’s Belt.

These and many other constellations and asterisms have long been considered arbitrarily formed under the influence of specific cultural knowledge.

In his 1981 book, At the Crossroads of Earth and Sky: An Andean Cosmology, Gary Wurton wrote: “Almost every culture seems to have recognized several of the same celestial groupings (e.g., the tight cluster of the Pleiades, V Hyades, the straight line of Orion’s belt), but large the constellation forms in European astronomy and astrology are simply not universally accepted; these forms were projected onto the stars because these forms were important objects or characters in the Western religious, mythological and calendar tradition.”

However, a new study published in the journal Psychological Science suggests there is more to the story than the juxtaposition of mythological figures with patterns in the night sky. According to the study, the cross-cultural similarity of asterisms may have more to do with human visual perception than a cultural need to align stories and myths with the cosmos.

“While ancient and modern cultures have adopted different names and histories for asterisms, more than a few asterisms are recognized in many cultures,” said Charles Kemp, a University of Melbourne researcher and lead author on the paper. “We’ve learned that basic aspects of our visual system can explain more constellations across cultures than previously thought.”

According to Kemp, psychologists and astronomers have previously noted that several groups of constellations catch the eye of just about anyone who looks at the sky, including the Pleiades (also known as the Seven Sisters and familiar from the Subaru logo) and Ursa Major (also known as the Plow or Wagon).

“We aimed to go beyond this small set of near-universal asterisms and characterize the long tail of asterisms that are not universal but are found in many cultures,” says Kemp.

To do this, he and his colleagues compiled a catalog of constellations and asterisms from 27 cultures to determine which groups are most common.

These cultures spanned six major regions Asia, Australia, Europe, North and South America, Oceania and included oral cultures such as the Inuit and literate cultures such as the ancient Chinese.

The researchers found that the list of repeating asterisms is not limited to well-known examples such as Orion and the Southern Cross. It also includes less visible asterisms such as Corona Borealis (Northern Crown) and Delphinus (Dolphin).

The researchers then used a computational model to determine how people group stars into constellations. They focused on two main principles: bright objects attract attention, and people naturally group nearby elements.

“These are two of a broader set of principles being discussed by psychologists who study perception,” says Kemp. “For example, one of the additional principles is that symmetrical groupings are usually noticed.”

The model grouped stars based on proximity and brightness, and these factors alone were enough to explain the many constellations that recur across cultures.

Thus, these results suggest that perceptual factors explain more of the structure of asterisms and constellations across cultures than previously thought, according to an article published in Psychological Science.

“I’m excited about how this line of work combines psychology and cultural astronomy,” says Kemp. “This combination is not common. I am also pleased that the very simple computational model that we present can provide some insight into a very rich aspect of culture: how people find meaning in the sky.

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