A typical Northern Hemisphere star trail with Polaris in the center. Michael Moselle/Flickr (CC By 2.0)
If you’ve ever looked at the night sky in the Northern Hemisphere, you may have noticed that gleaming object that everything appears to move around. What you’re seeing is the Polaris Star, also known as the North Star, which is approximately 430 light-years away from Earth and part of the constellation Ursa Minor.
Polaris has been a vital navigational reference for centuries, aiding travelers in finding their way due north, as it remains nearly stationary while other stars appear to revolve around it in the night sky. Let’s delve into the characteristics of this shining beacon and explore how to easily locate it.
What Is Polaris?
The Polaris Star, also known as the North Star, Northern Star or Pole Star, is a prominent star located in the Northern Hemisphere. It is specifically found in the constellation Ursa Minor, which is often referred to as the Little Bear or the Little Dipper. Situated nearly aligned with Earth’s rotational axis, it maintains a nearly fixed position above the North Pole.
Polaris is not just a single star but a trinary system, consisting of Polaris A, the primary component, and two smaller companions, Polaris B and Polaris Ab. (In astronomy, a trinary system consists of three celestial objects that are gravitationally bound to each other.)
Although it’s famed for its apparent steadfastness in our sky, Polaris A is not static; it’s a supergiant star, around six times as massive as the sun, and situated approximately 323 light-years from Earth. It pulsates, varying in brightness in a predictable cycle, and is categorized as a Cepheid variable star.
While Polaris is the current North Star, this title is transient due to the gradual change in Earth’s axial orientation, a phenomenon known as axial precession. In about 12,000 years, Vega, another bright star, will usurp Polaris as our guiding night sky landmark.
Polaris Doesn’t Rise or Set
The North Star is called that because its location in the night sky is almost directly over the North Pole, according to Rick Fienberg, a Harvard-trained astronomer and former press officer of the American Astronomical Society.
“So, if you were to stand at the North Pole — latitude 90 degrees north — at night and look straight up, you’d see Polaris directly overhead,” Fienberg says via email. “From other latitudes in the Northern Hemisphere, if you face due north at night and look the same angle above the horizon as your latitude (for example, look about halfway up — 45 degrees — if you live in Portland, Oregon, at latitude 45 degrees north), you’ll see Polaris shining there.”
Polaris is attention-getting, because unlike all the other stars in the sky, it can be found in the same location every night from dusk to dawn, neither rising nor setting, according to Fienberg. Its looming presence leads some people to think of it, mistakenly, as the brightest star in the sky (it’s actually the 48th brightest).
Even so, it’s about 2,500 times as luminous as our sun because it has more mass and a much larger diameter. But Polaris also happens to be far away for a star that’s visible with the naked eye, which reduces its brightness.
Has Polaris Always Been the North Star?
It may be hard to believe, but Polaris hasn’t always been celestial royalty. In fact, Ancient Egyptian astronomers in the Old Kingdom, between 4,700 and 4,100 years ago, had a different North Star, which they symbolically represented with a female hippopotamus, according to Giulio Magli’s book, “Architecture, Astronomy and Sacred Landscape in Ancient Egypt.”
That’s because what humans perceive as the North Star changed over time.
“If you picture a line connecting Earth’s North and South Poles as the axis around which Earth rotates, that axis is slowly moving in its own circle,” explains Christopher Palma, associate dean of the Eberly College of Science at Penn State University, in an email. “Often, this is compared to what happens when a top or a spinning coin start to ‘wobble’ before falling over on their side. We say that Earth’s North Pole is ‘precessing,’ that is, the line that goes from the North Pole to the South Pole traces out a circle with a period of 26,000 years.”
As a result, “over very long time periods (more than a few thousand years), the North Pole moves with respect to the stars,” Palma continues. “So thousands of years ago, people on Earth saw the star Thuban in [the constellation] Draco appear due north, instead of Polaris.”
How to Find the North Star in the Sky
Finding the North Star can be a fun and useful skill, especially if you’re navigating at night. Before you embark on your star-hunting mission, ensure you’re in a location with minimal light pollution. Polaris is always due north and is roughly aligned with your latitude, making it higher in the sky the further north you are.
Locate the Big Dipper. Begin by identifying the Big Dipper, which is one of the most recognizable constellations in the northern sky. Look for a formation of seven bright stars that comprise the “dipper” shape: Four stars form the “bowl” and three form the “handle.”Follow the pointers. Focus on the two stars forming the outer edge of the Big Dipper’s bowl. These are Dubhe and Merak, often referred to as the “pointer stars” because they guide you to Polaris. Imagine a straight line extending from Merak (the bottom star) through Dubhe (the top star).Reach polaris. Extend the imaginary line from the pointers approximately five times the distance between Dubhe and Merak. The bright star along this line is Polaris. It should be relatively isolated from other bright stars in its vicinity.Confirming polaris. Polaris is at the tip of the handle of the Little Dipper (Ursa Minor). Confirming it, you might see a fainter set of stars forming a smaller dipper shape, with Polaris being notably brighter.
The North Star in Navigation
Polaris seems to have been first charted by the astronomer Claudius Ptolemy, who lived in the second century C.E. The star’s location close to the celestial North Pole eventually became useful to navigators.
“At night, in the Northern Hemisphere, if you can see Polaris, you can always tell which way is north (and, by extension, which ways are south, east and west),” Fienberg says. “It’s true now, it’s been true for hundreds of years (including during the Age of Exploration in the 15th through 17th centuries), and it’ll be true for hundreds more years. You can also tell your latitude, since the angle from the horizon to Polaris is the same as your latitude (to within a degree, anyway). Once you travel south of the equator, though, Polaris drops below the horizon, so it’s no longer useful as a navigation aid.”
That said, a navigator using Polaris has to take into account that the star isn’t precisely over the North Pole but instead has an offset of 39 arc-minutes, explains Rich Schuler, a professor of astronomy, in an email interview. (He’s author of this 2002 primer on the North Star in Scientific American.) That corresponds to an error of 44.7 miles (72 kilometers), he says.
Here’s Why the North Star Twinkles
One of the other things that’s intriguing about Polaris is that it’s what astronomers refer to as a Cepheid Variable, which is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude.
“This star pulsates because it is in a state that is unstable,” says Palma. “It will swell up, and when it does, an outer layer of the star becomes transparent, which then makes the star cool off. As a result of it cooling off, it will shrink until it becomes opaque again, which causes it to heat up and swell again. It will do this over and over again, pulsating in and out, which causes its brightness to fluctuate.”
This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.
North Star FAQ
Why is the North Star so special?
The North Star, also known as Polaris, gets a lot of attention because unlike all the other stars in the sky, it remains in the same location every night from dusk to dawn, neither rising nor setting.
What is Polaris?
Polaris, also known as The North Star, is a prominent and nearly fixed star located in the northern celestial hemisphere.
How far is the North Star?
The North Star is approximately 323 light-years away from Earth.
Where is the Polaris star?
The Polaris star is part of the constellation Ursa Minor and is located almost directly over the North Pole.
Is the North Star the brightest star?
Its looming presence in the sky leads some people to think of it as the brightest star in the sky, but it’s actually the 48th brightest.
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