I was going to use this week to talk about some of the iconic, recognizable constellations in the winter sky (Northern hemisphere), but realized the moon would be plowing through them this week, washing out the stars and making them less visible.
So instead, while Venus and Mars continue to shine in the west, and the moon waxes to full (Thursday) and marches eastward across the southern sky, turn around and look north.
Polaris, the North Star, is one of the most useful stars in the sky.  Perched over the Earth’s geographic north pole, the entire sky seems to revolve around it, and finding it is an easy way to keeping your bearings at night.
Most people are familiar with using the Big Dipper (in Ursa Major, the Great Bear) to find Polaris:  Follow the line formed by the last two stars of the dipper and the first bright star you encounter is Polaris.  The Little Dipper, part of Ursa Minor, the Lesser Bear, hangs straight down from Polaris this time of year, curving toward the Big Dipper’s handle.  Most of its stars are fairly faint, except the two at the end of the dipper (more like a ladle), which are also known as the “Guardians of the Pole”, circling it every day as they do.
This is all fine and good, but you’ve probably noticed that at this time of year, soon after sunset, Ursa Major is so low on the horizon as to be almost invisible, and using the Dipper to pinpoint Polaris is not an easy task.
So, instead, look to Cassiopeia, the distinctive “W”, or “M” shaped constellation that is now at it’s highest point all year, just north of the zenith, almost straight up.  I like to think of Cassiopeia as a “W”, regardless of orientation.  At the moment, she’s upside down, but still a “W”.  You’ll note that the “W” is fairly open on the left, and more acute on the right.  If you picture a line starting from the bottom point of the “V” that forms the more open half, bisecting the triangle formed by its neighbors, this line ALMOST hits Polaris.  It’s a useful trick to know when Ursa Major is hidden, and you still need a good bearing.
stars-north-pole
A couple anecdotes about these two constellations – in Greek mythology, Cassiopeia was a queen, mother of Andromeda.  She was also vain, and felt that she was more beautiful than the Gods.  Posiedon punished her by ordering a sacrifice, commanding that Princess Andromeda be chained to a rock and left as lunch for a sea monster (Cetus in some tellings, but kids in my demographic recognize the monster as the Kraken in “Clash of the Titans“).  Andromeda was rescued by Perseus, who turned the monster to stone using the severed head of Medusa.  As a plan B, Posiedon placed Cassiopeia in the heavens, on her throne, but near the pole so she would spend half of each night upside down, presumably in humiliation.
Ursa Major is recognizable to most people, or at least its prominent Big Dipper asterism is – the entire constellation is substantially bigger – the Dipper makes up the bear’s torso, with the handle as his tail.  Despite the really long tail (for a bear), many cultures across the globe have seen a bear in these stars.  Native Americans thought the behavior of the bear was an indication of the seasons – right now, the bear has gone underground, hibernating.  As spring approaches, he’ll be starting the evenings climbing out of his den, spend the summer high in the sky, and start heading down again in the fall.
Another interesting point, the star at the bend in the handle is actually a naked-eye binary, or double star system. Native American legends referred to these two stars as the Squaw and Papoose, but we know them today by their Arabic names.  The brighter is Mizor, the dimmer, Alcor.  In some ancient cultures, being able to resolve the two and see both was a test of eyesight, but on a clear night seeing both isn’t really difficult, and binoculars make the two very distinct.  If you were to zoom in with a powerful telescope, you’d see that Mizor is actually a cluster of four stars, and Alcor is a binary, itself, so the “two” stars are actually a complex system of six individual stars!
Go out and find Polaris while enjoying the full moon this week.  It’s a good star to know, and it’s good to know how to find it even when the Dipper is hidden!
Troy
flying-squirrel.org

2 thoughts on “Astronomy: Week of 1/8/17 (Two Ways to Find Polaris)

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