The North Star has remained an eternal reassurance for northern travelers over the centuries. But recent and historical research reveals that the ever-constant star is actually changing.
After dimming for the last few decades, the North Star is beginning to shine brightly again. And over the last two centuries, the brightening has become rather dramatic.
“It was unexpected to find,” Scott Engle of Villanova University in Pennsylvania told SPACE.com. Engle investigated the fluctuations of the star over the course of several years, combing through historical records and even turning the gaze of the famed Hubble Space Telescope onto the star.
(In)constant as the North Star
Scientists have known since the early 20th century that the familiar star was part of a pulsating class known as Cepheid variables; its variations were suspected as early as the mid-1800s. But unlike most Cepheid variables, the pulses of Polaris are very small.
“If it had not been so popular as the North Star, we likely wouldn’t have known it was a Cepheid until modern times,” Engle said.
In the early 1990s, scientists realized that the oft-lauded brightness of Polaris was beginning to decline. Engle and his group began to research the star around the beginning of 2000, when they found that the dropping brightness was on the rise again.
“It started increasing rather rapidly,” Engle said.
Curious, the team began to search historical records to see what other measurements they could find. Combing through data from the past century, they compared the information on Polaris with observations of other celestial bodies from the same telescopes and details about the instruments to compare the relative brightness of Polaris over the years. They found that the star had grown brighter over the past hundred years.
The next step was to determine just how far back the increasing brightness went. Engle pursued observations by Danish astronomer Tycho Brahe in the 16th century and Persian astronomer Abd al-Rahaman al-Sufi in the 10th century, using information from historical texts to determine just how bright the star was in the ancient sky.
According to Engle, if we take the measurements of al Sufi and Ptolemy at face value, the North Star has brightened by about two and a half times over the last two centuries. Modern interpretations of the historical data indicate that it could be as much as 4.6 times brighter than it was in ancient times.
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