Learning the Constellations - Pole Stars & Pointers The Dippers

Pole Stars & Pointers - Learning the constellations from the top (northern hemisphere) - Ursa Major The Great Bear or big dipper, the pole star and Ursa Minor the little dipper. From the upcoming book on AstronomyForum.net and TelescopesAstronomy.com

 

 

 

Pole Stars & Pointers for the Northern Hemisphere - Starting at the Dippers

It is necessary to know the Dippers as they can be used as a starting point by-which to find all the other constellations. They may be seen in the northern heavens, high up during the first half of the year and near the horizon during the rest of the year.

 

The Dance of the Bears Ursa Major and Minor Throughout the Seasons

The idea of dancing was connected with Ursa Major, as well as with the other circumpolar constellations, by the ancients.  Sir G. C. Lewis says that this was derived from the circular dances of the Greeks.  The two bears (Ursa Major and Ursa Minor) were imag ined reeling round the pole like a pair of waltzers

Do note from the diagram below that the orientation of this constellation varies with the season. Moreover, you may see it in one position as you go out to dinner and in a different one as you return from a dance late the same night. This is confusing, I admit.

Beginners Guide to the Big Dipper - Ursa Major

The real name of the constellation is Ursa Major, The Great Bear, but it does not look so much like a bear as it does like a dipper.  The handle forms the bear's tail, and real bears have no tails, whereas old dippers often have such handles.  The seven stars which form the "Great Dipper" are always in our northern sky.  That we do not see them by day is wholly due to the fact that the daylight hides them.

Note that the pole star belongs to the constellation Ursa Minor, the Lesser Bear;

 

 

 

 

 

 

 

 

Finding Other Constellations from the Big Dipper Using Its Pointer Stars

Alpha and Beta, the pair in the outer side of the bowl, are often called the Pointers, because an imaginary line drawn through them and extended pole wards nearly hits the pole-star at a distance of about thirty degrees

The two stars in the side of the Dipper, opposite to the handle, are called " The Pointers," because they point to the Pole Star, or North Star.

The Polar Star

This star is nearly due north, and it is the only star in the heavens that does not seem to change its place. All the others revolve about it as a center. The star's name is Polaris, and it belongs to the constellation Ursa Minor, The Little Bear. Like the Great Bear, this constellation resembles a dipper more than it does a bear. Some of the stars are rather faint, but the dipper can be made out. The Little Bear also has a long tail formed by the handle of its dipper, and Polaris is at the extreme end. As the end of the tail is fixed and the bear is swung around by it daily, possibly this accounts for its length. A few thousand years ago Polaris was not the pole star, nor will he be a few thousand years after.

Most easily recognized and most important of all these constellations is the Big Dipper.  Ursa Major, as it is known to astronomers, means Greater Bear, but no name could suit this group better than the "Dipper" for it looks exactly like one.

It is with the use of the Big Dipper, more widely known than any other group, that the Pole Star is found.  By following a line drawn through the pointers of the bowl (the two stars directly opposite the handle), and continuing through the top of it one comes to Polaris, the North Star, guide of mariners for untold generations.  Polaris, which is about twice the moon's apparent diameter from the true north celestial pole, does not stand alone in the sky; instead it is the brightest star of the Little Dipper, or Ursa Minor.  This group is more difficult to make out than is its larger brother, for the stars are fainter and of varying degrees of brightness.  Two, which occupy a position in the bowl similar to that of the pointers in the larger constellation, are fairly bright and are easily found on a clear night.  They lie between the pole and Draco, and because they seem ever to be on guard against an attack by the dragon upon Polaris, they are known as the guardians of the pole.

 

 

 

 

 

 

Ursa Major The Constellation - A Visual Guide

Directly north of Leo Minor is one of the great figures of uranography, and one of the most familiar to ordinary observation of all the constellations Ursa Major, the Greater Bear.  Indeed, in the northern hemisphere because of its situiation within about forty degrees of the north polar star, Ursa Major is probably seen and recognized in the heavens more than any other group of stars.

It is especially known by the celebrated figure of the Great Dipper, formed by seven stars in the flank and tail of the Bear.  In the latitude of New York the Great Dipper never sets, the star in the extreme end of the long handle just skimming the horizon in the evenings of November and December, while in May and June it is ahnost overhead.

Ursa Major, the Great Bear, known also as the Great or Big Dipper.  This is a large constellation, but only the seven stars composing the "dipper" are conspicuous, and we confine our notice to them. 

Ursa Major Greek Mythology

Calisto was the daughter of Lycaon, King of Arcadia, and was an attendant of the goddess Diana.  Jupiter fell in love with the beautiful princess Calisto, and his wife Jimo became enraged with jealousy and changed the princess into a bear.

Calisto, however, had borne to Jupiter a son named Areas, who became a famous hunter.  One day while hunting in the Arcadian forest he came upon a bear, and was about to slay it, not knowing that it was his mother.  Jupiter then interfered and changed Areas into a bear also and translated both to heaven.  Calisto became Ursa Major and Arcas Ursa Minor.  When Juno learned of this she was greatly displeased, and she went to Tethys, wife of Oceanus, the Ocean, and begged her to promise never to receive these bears beneath her waves.  Tethys promised, and as a result these constellations never set, but whirl forever round the pole.

 

Ursa Major a Visual Guide Walk-Through of the Constellation

Four stars form the bowl and three the handle; and the resemblance is the more perfect since all but one of the stars are of the same magnitude.

In this dipper the second star from the end of the handle is an object that carries us back to the days of the early Arabs.  This is the star Mizar and its faint companion Alcor which form a naked-eye double.  So difficult is it to see Alcor that this was the standard eyesight test given to recruits for the Arabian army.  Although to the casual observer the bowl of the dipper may seem almost devoid of stars, a careful count with the naked eye on a clear night will reveal ten or twelve faint ones.  In this area are located several famous telescopic objects.

The individual names of these stars, beginning with the northwestern corner of the bowl of the imaginary dipper, are Dubhe, Merak, Phaed, Megrez (the faint one), Alioth, Mizar (before mentioned with its companion, Alcor), and Benetnasch.  Their Greek letter names, in the same order, are Alpha, Beta, Gamma, Delta, Epsilon, Zeta, and Eta.

Alpha and Beta, the pair in the outer side of the bowl, are often called the Pointers, because an imaginary line drawn through them and extended pole wards nearly hits the pole-star at a distance of about thirty degrees.  These seven stars differ in color, al though the fact may not be apparent to hasty ob servation.  Alpha and Gamma are yellow.  Beta is greenish, and Zeta and Eta are brilliant white.  Delta, now so much fainter than its sisters that one feels a certain disappointment over the irregularity which it introduces into an otherwise perfect array of equal stars, seems formerly to have been as bright as any of them, and, in his time, Tycho Brahe, the famous Danish astronomer, estimated it of the second mag nitude, like the others.  It is probably a long-period variable.

The names of these seven stars beginning with the end of the handle are Ajkaid, Mizar, Alioth, Megrez, Ptiecda, Merak and Dubhe.  These are all second magnitude except Megrez, which is third magnitude.

In the middle of the handle is a famous naked-eye double, Mizar, whose companion, close by on the northeast, is named Alcor.  These stars are sometimes called the Horse and Rider.  Any good eye can easily separate them, and yet they were at one time regarded as a test of naked-eye seeing.

Dubhe is twenty-nine degrees from the Polar Star ; the top of the dipper is ten degrees in length and the bottom eight degrees; the two pointers are 5 degrees apart.  These distances should be carefully remembered for future use.

Lastly, the observer may turn to the pair Mizar and Alcor, the former the middle star in the Great Bear s tail, the latter 15 off.  It seems quite clear, by the way, that Alcor has increased in brilliancy of late, since among the Arabians it was considered an evidence of very good eyesight to detect Alcor, whereas this star may now be easily seen even in nearly full moonlight.  Mizar is a double star, and a fourth star is seen in the same field of view with the others.  The distance between Mizar and its companion is about 14 degrees; the magnitude of Mizar 3, of the companion 5 ; their colors white and pale green, respectively.