Anyone who looks up at the night sky and can identify a few stars, constellations or planets knows that everything is always moving.
Or is everything moving? Maybe we are the one who is moving.
There is an expression that your “North Star” is the thing that guides you. The actual North Star or Pole Star – which is named Polaris – is known for holding nearly still in our sky while the entire northern sky moves around it.
It really was a guiding star for ancient travelers and sailors. Like a compass, it showed you due North.
Polaris is located nearly at the north celestial pole which is the point around which the entire northern sky turns. If you painted stars on the ceiling of a room and had your own Pole Star at the center of the room and stood right below it, you could spin like a top and all the stars would circle over your head. Except for that Pole Star.
In my lifetime, the stars have been essentially fixed relative to one another, but over time they are moving around the center of the galaxy. I wrote earlier about how even the North star has moved and the Pole Star has not always been Polaris.
This photo of Aldebaran is cropped from one made of the Hyades star cluster, the nearest cluster to Earth.
Remember back in 2006 when the poor, old planet Pluto was demoted? A group of scientists decided that there are three main categories of objects in our solar system. There are Planets – 8 from Mercury to Neptune. There are Dwarf Planets – now to include Pluto and any other round object that “has not cleared the neighborhood around its orbit, and is not a satellite.” And there are Small Solar System Bodies – all other objects orbiting the Sun.
I felt bad for Pluto – and so did a lot of other Earthlings.
In 2015, I read that the waxing gibbous moon outside my window was moving toward the star Aldebaran, the brightest star in the constellation Taurus the Bull. Nothing odd about that. Normal movement.
But what I had not known until then was that Aldebaran also had a kind of demotion. It used to be the North Star, also known as the Pole Star. How does a star lose its rather prominent name and place in the sky?
You probably learned that Polaris is the North Star, but a long time ago Aldebaran had that honor. That was 450,000 years ago.
Back then, it appeared several times brighter in the sky then than it does now. In a way, it shared the title because it was very close to another very bright star, Capella, so they served as a double pole star. (This was 447,891 BCE, if you like precision.)
That’s pretty amazing, but it was a long time ago. What really hit me was that in this little solar system of ours and in our beautiful galaxy and this almost unimaginable universe, everything is always moving. The sky looked different hundreds of thousands of years ago.
This illustration shows the view as seen from present-day Arizona in 447,000 BCE when Aldebaran and Capella served as double pole stars. Illustration via Carina Software and Instruments and earthsky.org
The identity of the pole star shifts over time. This is due to the 26,000-year cycle of precession. (read more)
Most people believe the stars essentially fixed relative to one another. Within the scale of human lifespans, that is true. But stars are moving through space in orbit around the center of the galaxy.
The Earth is spinning as I sit here typing. It is making our Moon and Aldebaran shift westward but the Moon is moving to the east relative to the “fixed” stars because of the Moon’s orbit around us.
It is all so amazing. Some people think that looking up into that giant night sky makes them feel so small. I disagree. It makes me feel a part of something so enormous and grand.
For those of us in the northern U.S. or Canada or at a similar latitude, the Big Dipper is always above the horizon. That means it is described as circumpolar. The mnemonic to remember for the Big Dipper is “spring up and fall down” to describe its appearance in our northern sky.
The Big Dipper’s location at around midnight in each season. Image via burro.astr.cwru.edu
The Big and Little Dippers are asterisms – a prominent pattern or group of stars, typically having a popular name but smaller than a constellation. The Big Dipper ascends in the northeast on spring evenings, and it descends in the northwest on fall evenings.
“Follow the Drinking Gourd” is an American folk song that used “Drinking Gourd” as another name for the Big Dipper. The lyrics, according to legend, came from a conductor of the Underground Railroad, called Peg Leg Joe, as a way to guide some fugitive slaves.
The “drinkin’ gou’d” alludes to the hollowed out gourd used by slaves (and other rural Americans) as a water dipper. Used in the song, it was a code name for the Big Dipper which points to Polaris, the Pole Star, and to the North and freedom.
Polaris is a special star because it always stays in the same spot in the northern sky. The entire northern sky appears to turn around it because Polaris is located more or less above the northern axis (pole) of the Earth, and the wheeling of the stars across the dome of night is really due to Earth’s turning, after all. Polaris is part of the harder to find star pattern known as the Little Dipper.
Weekends in Paradelle 