North Star Closer to Earth Than Thought

Andrew Fazekas for National Geographic
December 5, 2012

Star trails—the results of a long exposure and Earth's rotation—surround the North Star.
Photograph by James Forte, National Geographic

Famous star's distance was overestimated in previous studies, astronomers say.

The North Star has been a guiding light for countless generations of navigators. But a new study reveals that its distance to Earth may have been grossly overestimated.

In fact, the North Star — also called Polaris — is 30 percent closer to our solar system than previously thought, at about 323 light-years away, according to an international team who studied the star's light output.

Using Russia's 6-Meter Telescope, the researchers were able to calculate the North Star's distance from our solar system by analyzing its spectrum of light and obtaining data on its temperature and changes in intrinsic brightness over time.

That significantly revises the previously accepted value of 434 light-years, which was obtained by the European star-mapping satellite Hipparcos in the 1990s. (Take a solar system quiz.)

The new discovery of a closer North Star is "most unexpected for what is considered to be one of the Hipparcos satellite's most solid results," said study leader David Turner, an astronomer at Saint Mary's University in Halifax, Nova Scotia.

(Also see "New Supernova Found 'Next Door'—Getting Brighter.")

North Star a Celestial Beacon

The North Star's claim to fame is due to its fixed position in the sky for Northern Hemisphere observers—aligned with Earth's northern axis—while other stars appear to wheel around it.

Known to fade and brighten over a four-day period, this celestial beacon of true north is considered the closest and brightest member of a class of stars called Cepheids that change in brightness over time. (See star pictures.)

The star is also a type of cosmological yardstick used by researchers to measure great cosmic distances out to billions of light-years.

For this reason, it's vital for our understanding of the cosmos that scientists get a reliable grip on the North Star's true distance, emphasized Turner, whose study will appear in Astrophysical Journal Letters.

For instance, research on dark energy — the mysterious force thought to be causing the universe to fly apart faster over time — is dependent on stars such as the North Star.

(See "New Galaxy Maps to Help Find Dark Energy Proof?")

Unseen Object Orbiting North Star?

The new results also located nearly a half dozen stars that appear to be surrounding the North Star and show signs that they have all once belonged to the same star cluster, which has now dispersed.

"This system is known to contain two other stars in addition to the Cepheid stars, but there may be yet another unseen object orbiting Polaris ... a massive orbiting planet for example," he added.

"There definitely remain a few oddities to keep Polaris an object of study for many years to come."

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Photo: James Forte
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