Mars and Saturn are still low in the south west 30 minutes after sunset. Enough about that. Let’s talk flags. The Territorial Flag and the Coat of Arms of Nunavut feature the North Star, Polaris, in their designs. Not to be outdone, the State Flag of Alaska consists of a blue background emblazoned with eight gold stars, seven in the shape of Ursa Major (the Big Dipper), and a larger one representing the North Star. By coincidence, the flag shows the positions of the star and Big Dipper as they would appear about 9pm if you went outside tonight.
The North Star is obviously important to northern communities as a constant beacon in the sky, especially during the long, dark months of winter. Historically, Polaris was used by sailors for navigation, mainly because it’s always in the same place even as the rest of the sky rotates around it. However, it holds a special place with astronomers as well. Once it’s dark enough that a decent number of stars show up, grab your Alaskan flag, step outside, and face north. About half way up the sky, you will find Polaris with the Big Dipper off to its left (below it by midnight).
Looks pretty ordinary, but looks can be deceiving. Polaris is a yellow supergiant, 4.5 times the size of the Sun, at a distance of about 434 light years. It is also a triple star, with one of the companions easily visible in small telescopes. To be accurate, maybe we should be calling it the North Stars. But, what makes it really special is that Polaris is also a low amplitude Population I classical Cepheid variable, and the closest one of its kind. Refresher: a Cepheid variable is a star that pulsates in size and brightness on an extremely regular period.
The pulsation rate is closely tied to the brightness, so depending on how fast it’s pulsing, you can tell how far away it is by how bright it appears. Cepheids are among the basic measuring sticks for distances across galaxies, so having one virtually on our doorstep to study is a gift. Polaris will always be our neighbourhood Cepheid, but thanks to an Earth-wobble called precession, its current position of official Pole Star is temporary.
Turn around, face south and look up. Just short of overhead, you will spot Vega, the second brightest star north of the equator. Twelve thousand years ago, Vega was the North Star, and in another fourteen thousand, it will be again.
It is unclear as to whether Alaska will have to change its flag. But, for now, appreciate that the easiest star in the sky to find holds down two very important jobs, and it’s available on any clear night, in exactly the same place, twelve months a year, from your own back yard.
