My Guiding Star

star spin

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.

The universe is still at times unimaginable.

Solstice Fireballs

Ursa Major
Ursa Major – the Great Bear – and the Big Dipper where the Ursid meteor shower seems to originate.

As is often the case here in December, viewing conditions for watching meteor showers recently for the Geminids were lousy – clouds and rain. There’s another chance this week for a smaller event.

The annual Ursid meteor shower was visible to some starting earlier this week (clouds and rain for me again) but it typically peaks around the Winter Solstice. The Ursids are not as impressive a show as the Geminids, but I’ve missed seeing almost any meteors all year so I’m hungry to catch at least a few this time. And with my sons and daughters-in-law visiting for the holidays, I will probably push them outside on a clear night to watch for a fireball.

The Ursid meteor shower runs from about December 17 to 26 each year. I associate it with the Winter Solstice and Christmas so it does have a kind of special place in my celestial calendar.

waning crescent moonThe Moon will be in its waning crescent phase this weekend which will make the sky much darker than it was for the Geminids. On Christmas Day there will be a dark as possible New Moon.

The Ursids may show 5-10 meteors per hour in a dark sky with a rare burst of more (near 100) in some years.

The Ursids get there name from where they appear to originate. Look to the Big and Little Dipper asterisms which are in the constellations Ursa Major and Ursa Minor.

Ursa Major, the Great Bear, is a constellation in the northern sky. The Latin name means “greater (or larger) she-bear” to contrast it with the nearby Ursa Minor, the lesser bear. It was one of the original 48 constellations listed by Ptolemy in the 2nd century AD.  Ursa Major is well known for the asterism of its main seven stars, which we call the Big Dipper which resembles the Little Dipper in Ursa Minor. The bears’ tails are the handle of the dipper cups.

Ursa Minor may be smaller but it contains Polaris, better known as commonly the North Star or Pole Star, which is the brightest star in this constellation.

For those of us in the Northern Hemisphere this weekend, the Big Dipper is pretty far up in the north-northeast sky by midnight. From midnight into early morning is a good time to watch. I think I’ll make some nice late-night hot toddies tomorrow night to lure the kids outside.

Ursa Major Never Sets

The stars move with our seasons. For most of us, some move below the horizon and we lose sight of them for part of the year. But the circumpolar stars stay above the horizon all hours of the day, every day of the year. They are there now, even if it is daylight as you read this, they are there. there’s not a lot you can count on here on Earth – or even in the heavens – but you can count on them.

The Big Dipper asterism is the best known of the circumpolar groups at all latitudes north of 41 degrees north latitude. (That is the northern half of the mainland United States and most of Europe.)

The Big Dipper is part of a bigger constellation, Ursa Major or the Great Bear.

In Greek mythology, the god Zeus had fallen in love with the maiden Callisto. In a story that would make the news today, and get Zeus some bad headlines, Zeus got her pregnant. Callisto was a nymph in the retinue of the goddess Artemis. But she would not be with anyone but Artemis. Zeus disguised himself as Artemis and seduced Callisto. When the child Arcas was born, Zeus’ wife Hera turned Callisto into a bear in revenge.

Callisto wandered the forest for years in bear form, until a chance meeting with her son, Arcas. He was the king of Arcadia and a great hunter. He raised his spear to strike at the bear, not knowing it was his mother. Zeus stepped in and sent them up to the heavens with Callisto as the Great Bear and Arcas as Bootes the Herdsman. (Or maybe he is Ursa Minor, the Little Bear,  depending on whose mythology you follow.) Hera was not pleased that Zeus stepped in, so she wever, and conspired with the gods of the sea so that the Bear could never swim in the ocean. That is one explanation – totally unscientific – for why Ursa Major never sets

The Big Dipper is circumpolar, so it is visible year round. It is up in the spring and down in the fall. The pointer stars in the bowl of the Big Dipper always point to Polaris, the North Star |  |  Image via Chris Mihos, Department of Astronomy, Case Western Reserve University

Where are you? If you’re with me in the Northern Hemisphere, every star north of the celestial equator is circumpolar, and every star south of the celestial equator is below the horizon. At the Earth’s South Pole, every star south of the celestial equator is circumpolar, whereas every star north of the celestial equator remains beneath the horizon.

And at the Earth’s equator, no star is circumpolar because all the stars rise and set daily in that part of the world. You can actually see every star in the night sky over the course of one year.

Follow the Drinking Gourd

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.

big_dipper_thru_seasons
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.