Here’s why people picked certain stars as constellations

A high school student simulated how humans trace patterns in the night sky.

The Big Dipper’s stars are a celestial landmark. Visible in the Northern Hemisphere’s night sky, the stars draw out a shape like a scoop with a handle. Beginner stargazers can easily pick it out. Now, scientists have shown that three factors can explain why certain groups of stars form such recognizable patterns. One is how bright the stars are. Another is how far apart they are. And a third has to do with how human eyes move.

The Big Dipper is part of the constellation Ursa Major. That’s one of many star groupings that people in the past selected for their shapes. Some shapes were said to depict animals, people or objects. Sophia David wondered why people selected these star groupings. She is a high school student at Friends’ Central School in Wynnewood, Penn.

“Ancient people from various cultures connected similar groupings of stars independently of each other,” said David. That suggests that different people were perceiving the stars in the same way. So David teamed up with scientists at the University of Pennsylvania in Philadelphia. She presented their work March 18 at an online meeting of the American Physical Society.

The researchers thought about how the eyes travel across this night sky. Human eyes tend to move in discrete jumps, called saccades (Seh-KAADS). That’s when both eyes quickly shift from one point of interest to another. The team created a computer simulation based on the distribution of saccade lengths. They also included two basic details of the night sky as seen from Earth. The first was how far apart different stars appear from one another in the sky. The second was how bright various stars are.

The technique could pick out single constellations. One constellation it picked out was the star grouping known as Dorado, the dolphinfish. The researchers also used the technique to map the whole sky. It generated groups of stars. The scientists compared those groups to the 88 modern constellations. Those are groups of stars recognized by the International Astronomical Union. The two sets of star groups mostly matched. That confirmed the method worked to explain how the constellations came to be.

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