Milwaukee Astronomical Society



The Polar Constellations

  1. We officially start our tour of the Spring Sky by turning our attention to the North. Anybody recognize anything? (Someone will recognize the Big Dipper). {Trace out the Big Dipper}.

  2. It's really not a constellation, it's what's called an 'asterism', a highly recognizable part of a constellation. The full constellation actually is Ursa Major. {Trace out the full constellation of Ursa Major.}

  3. The Bear's paws are also known as the Three Leaps of the Gazelle. This asterism is the sequence of three pairs of stars - normally seen as the paws of Ursa Major. The story is that Leo the Lion startled a gazelle, who in turn dashed off across a great celestial pond, leaving a pair of stars marking each of the three leaps.

  4. The stars of the Big Dipper, with the exception of the tip of the handle and the tip of the cup, are all moving in the same direction -- up and to the left, or toward the Northwest. Because they're close together (all are about 75 light years away) and moving through space in the same direction at the same speed, these stars are believed to have formed together from the same original nebula. This group, known as the "Ursa Major Moving Group", is officially the closest star cluster to us, and includes stars that are scattered across the sky all the way from Boötes & Corona Borealis to Auriga and Taurus. The reason they seem to be everywhere is because our 5 billion-year-old sun has drifted into the outer regions of this group of 500 million-year-old youngsters.

  5. We can find two of the best and brightest galaxies in the sky just above the two stars that form the neck of the Bear -- they are M81 and its neighbor M82. Use the binoculars and follow the line of the Bear's neck to a skinny triangle, then go sideways to find a pair of stars that point the same direction as the triangle does. Just a little farther you find M81, a faint fuzzy spot just off the end of the arc of three faint stars nearby. See it? This faint fuzzy spot is actually a spiral galaxy, 12 MILLION light years away. When I get this one in the telescope you'll see that there are actually two galaxies there. The other one is M82, and it's called the Cigar Galaxy because of its shape -- it looks flatter than M81 because we're seeing it edge-on. M82 is about the same distance as M81, and is called a "starburst galaxy", because the gravity from M81 is causing a burst of new star formation in the Cigar. So even though M82 is only about a third the size of our Milky Way galaxy, it is five times brighter!

    M81 is on the left, M82 is at the right
    M81 and M82

  6. The Big Dipper is a polar 'constellation' -- one that is very close to the North Pole. If stars are close enough to the pole they never set below the horizon and we can see them all year long. Can anyone spot the Pole Star? How do you find it? That's right, the two stars at the front edge of the cup are pointer stars and point to the North Star, whose actual name is Polaris. Go up from the cup to find Polaris.

  7. Since the earth's north pole points to Polaris and the earth rotates around its poles, all the constellations seem to rotate around Polaris, including the Big Dipper. You can tell time using the Big Dipper -- it serves as a 24-hour clock.

    Click on the little clock here for more information.

  8. Polaris is a part of the constellation Ursa Minor, more commonly known as the Little Dipper. Polaris is at the tip of the handle. {Trace out the Little Dipper.}

  9. Threading his way between the Big Dipper and the Little Dipper is Draco the Dragon. {Trace out Draco.} Draco starts off with two bright yellow eyes (actually one's yellow, one's orange), and then winds around the little dipper with its tail between the two dippers. This is a very cool-looking constellation, a rare one that looks like the monster it is supposed to be, glaring yellow eyes and all. The head of Draco forms a distinct asterism, known as "The Lozenge". Who's got the binoculars? Use them to find Draco's eyes, then go down to find the next star in the Lozenge closest to the eyes -- ν (nu) Draconis. Notice anything? That's right, it's a double star, and a very neat one in binoculars, tight together and exactly equal in brightness.

  10. So the Big Dipper points to the North Star -- it also points to other important stars -- in fact it points us to all the important constellations we visit tonight. You can follow the two stars across the top of the cup and they lead you to the northernmost bright star Capella, in the constellation Auriga. If, instead of going up from the front of the cup, you go down from the back of the cup, you end up at the star Regulus in the constellation Leo. And... if you go across the cup, from the back top to the bottom front, you end up at Castor in Gemini. You can continue that line on until you get to Betelgeuse in Orion, the brilliant red star to the west. We'll come back and hit each of these one at a time.

  11. The three stars of the dipper's handle are pointers as well -- you follow the arc of the Dipper's handle and "arc to Arcturus", then "spike to Spica" - two very important stars that we will get to presently.

  12. Wait a minute is that really three stars in the Dipper's handle or is it four? Looky there the middle star seems to have a companion -- the bright star is Mizar and the companion is Alcor. Who can see the companion?

    That was used by ancient Greek and Arab armies as an eye test. Some see them as a horse & rider. The Europeans saw the handle of the dipper as the tail of the Great Bear. Since bears don't have tails they danced around it by explaining that when the gods lifted the bear to the sky the tail got stretched out. Pretty lame. The Indians, who knew darn right well that bears don't have tails, saw the three stars of the handle as hunters chasing the great bear (interesting that they also saw a bear). When the constellation Ursa Major sets in the fall, the Indians explained that the hunters catch up with him and shoot him with their arrows, which is why the leaves on the trees turn red. Anyway the three stars are hunters and one of them brought his dog, so Mizar is a hunter and Alcor is his dog. Or another story is that there are three hunters pursuing the bear and one brought a pot to cook the bear in (optimistic). So Mizar is a hunter and Alcor is his pot. Yet another story involves the Pleiades. This is a star cluster in the constellation Taurus (a winter constellation). It is called "the Seven Sisters" and those with very sharp eyes can see seven stars but most people can only see six. So the story is that Mizar is riding off with the Seventh Sister.

    But wait there's more! When we put the telescope on these two you'll see that Mizar is really a double star itself! So these three form a triple star. But wait... that's right... there's MORE! In reality each of the two stars that make up Mizar is a double star, too close for us to see even with a big telescope, and for that matter, so is Alcor! So Mizar & Alcor comprise a SIX STAR SYSTEM!!

Back to Retreat of the Titans Go to Spring Index On to Auriga


Your questions and comments regarding the Stargazing section are welcome. You can e-mail the author, Randy Culp for inquiries, suggestions, new ideas or just to chat.
Updated 18 July 2023