Look-UP

by Mitchell Tester, College Student

The North Star

If you go outside any night with the sky clear and look directly above, you’ll notice a “fixed star.” That star is what we call the North Star, or its official name, Polaris. This star is in the constellation Ursa Minor, also known as the Little Dipper.

The reason that this star is considered to be fixed in the northern sky is due to its proximity to the north celestial pole. Earth’s axis of rotation points almost directly at it. Technically, Polaris does move, although the circle that it spins in is so small that it’s invisible to the naked eye; that is why we refer to it as being stationary.

Polaris has been a navigational aid for people for thousands of years. Ancient civilizations, such as the Vikings, Arabs, and Chinese, utilized it to explore the world.

Polaris is 448 light-years away, so let us travel there.

When you arrive at Polaris, you will notice something peculiar. Polaris is actually a triple-star system. It consists of two stars orbiting quite close to each other, Polaris Aa and Polaris Ab, and a distant star, Polaris B. Although to us on Earth, these stars appear as one. Some stars do not actually have planets orbiting them. 

Various reasons as to why a star (or stars) does not have planets that orbit it exist. Some of those reasons are due to harsh formation conditions, while others are due to our shortcomings in planetary observations. Harsh formation conditions can lead to massive stars blowing away any early planet formation by way of intense radiation, never even allowing the chance for a planet to be formed. Although gravity is key to planetary formation, at times it can also disrupt the planets from forming. This comes in the form of multi-star systems and the chaos from the stars’ gravitational pull—this could very well be the case for Polaris. The most common reason, though, as to why planets do not form is due to there simply not being enough heavy elements (think metal) for core building; a strong core is integral for planets to exist.

Earlier, I mentioned shortcomings in planetary observations; this is another reason why stars do not have planets orbiting them, or a better way to put it is that they appear not to have planets orbiting them.

When you’re dealing with stars, distance and brightness play key roles in what we are able to see. In the case of Polaris, we say that no planets are orbiting the three-star system, but we are actually unsure. Due to the chaotic nature of both Polaris Aa and Polaris Ab, it is quite unlikely that a planet is orbiting the two. As for the more distant star, Polaris B, it is not impossible. Possibly, with the advancement of technology, we will discover if Polaris is home to planets. Polaris Aa is what we call a Cepheid variable star, which means that it changes brightness from its pulsing. This makes it very difficult for us to detect any planets; we refer to this issue as stellar “noise.”

Cepheid stars are young, massive stars. The pulsating comes from layers of helium gas trapping heat (light) and then releasing the heat (light). This rhythm causes the star to appear as if it is pulsating. The northern star, like everything in our universe, is temporary. In roughly 1,000 years, Polaris will no longer be our northern star, but a different star, named Gamma Cephei (Errai). After stars such as Deneb and Vega follow, humans will return to using Polaris as their northern star around 28,000 AD. This 26,000-year cycle is simply due to the gravitational pull of both the Sun and Moon, causing a wobble of Earth’s axis (think of a spinning top), which is known as “axial precession.”

The North Star (Polaris) is ingrained in humanity and history and is believed to symbolize guidance, hope, purpose, a moral compass for personal journeys, and steadfastness. The North Star (Polaris) is both a reliable celestial beacon used for navigation and a deep-rooted symbol. Not only has it been a way for us to navigate and discover the world, but it has also been seen as an anchor of stability. Something that we as a human race can count on.

The North Star as seen from France.