Ursa major, la constelacion




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URSA MAJOR, LA CONSTELACION

por Carlos Andrés Carvajal T.

Tomado de http://almaak.tripod.com/temas/constelaciones/osa_mayor.html
Lo Osa Mayor
Esta constelación es sin lugar a dudas una de mas mas famosas de las circumpolares del norte principalmente por su asterismo formado por 7 estrellas y conocido como el cucharón (la cola de la Osa). Este asterismo desde la antigüedad a llevado a los navegantes del hemisferio norte a ubicar la estrella polar. 
Abreviación: UMa

Forma Posesiva: Ursa Majoris

Ascensión Recta: 10.67 horas

Declinación: 55.38°


Mitología
Calixto era la hija del rey Licaón y desde pequeña fue elegida como compañera de Artemisia y como la diosa había dado votos de castidad todas sus acompañantes igualmente debían permanecer vírgenes.
Sin embargo Zeus comenzó a rondar a Calixto hasta que haciéndose pasar por la misma Artemisia se acercó  a ella y la sedujo. De este encuentro Calixto quedó embarazada. Al darse cuanta Artemisia -otros dicen que a pedido de Hera la esposa de Zeus- la convirtió en Osa para cazarla y matarla.
Zeus envió al cielo a la Osa para evitar que esto sucediera. El hijo de la Osa, Arcade la acompaña en el cielo en forma de Osa menor
Objetos de Interés
Mizar (Zeta UMa) Es la estrella del medio del mango del cucharón. Es una doble que puede resolverse con el ojo desnudo, su compañera se llama Alcor. Mizar es una doble por si misma (Mizar A y B) que a su vez son dobles espectroscópicas.

M40. AR: 12h 22m 24.0s Dec: +58°05'00" (Época 2000). Es una estrella doble que Messier observó inicialmente como una nebulosa y la incluyó en su catálogo. Se conoce también como Winnecke 4, Se encuentra a medio grado al norte de gamma UMa.

M81 (NGC 3031) AR: 09h 55m 36.0s Dec: +69°04'00" (Época 2000). Hermosa galaxia espiral localizada e el mismo campo que M82 (NGC 3034) AR: 09h 55m 48.0s Dec: +69°41'00" (Época 2000).

M97 (NGC 3587). AR: 11h 14m 48.0s Dec: +55°01'00" (Época 2000). Llamada la nebulosa lechuza, es una de las nebulosas planetarias mas grandes observadas con telescopios pequeños. Su forma es distinguible pero se requieren grandes aperturas para detectar su cara de lechuza..

M101 (NGC 5457) AR: 14h 03m 12.0s Dec: +54°21'00" (Época 2000). Galaxia espiral de las más grandes observadas, se localiza a a 5º al este de Zeta UMa, 

M108 (NGC 3556). AR: 11h 11m 30.0s Dec: +55°40'00" (Época 2000). Galaxia localizada a un 1º de la anterior.

M109 (NGC 3992). AR: 11h 57m 36.0s Dec: +53°23'00" (Época 2000). Galaxia espiral barrada brillante cercana a Gamma UMa.

NGC 3593. AR: 11h 14m 36.0s Dec: +12°49'00" (Época 2000). Galaxia espiral barrada cercana a la anterior .
AGREGAR

Tomado de http://condor.stcloudstate.edu/~physcrse/astr106/stories.html


The Bear and Zeus

The Great Bear according to one story is connected with the birth of Zeus along with the Lesser Bear Ursa Minor. According to this story the Great Bear is the tree nymph Adrasteia.


The Princess Callisto

According to another story the Great Bear represents one of the many loves of Zeus, Callisto, the daughter of King Lacaon of Arcadia. Callisto was fond of hunting and joined the retinue of the Artemis, the Goddess of the Hunt. Callisto became a favorite of Artemis, to whom she swore a vow of chastity.


A Divine Seduction

On a visit to the earth, Zeus happened upon the lovely Callisto sleeping in a forest grove. Zeus approached her wearing the guise of Artemis. As he embraced her he revealed himself and had his way in spite of the struggles of the girl. As a result of this encounter, Callisto became pregnant. Artemis was furious at this and banished the girl.


Hera's Revenge

Callisto bore a son, who was named Arcas. Poor Callisto became the target of the wrath of the jealous Hera, the spouse of Zeus. Hera changed the poor girl into a bear.






Arcas Chases the Bear

For fifteen years poor Callisto wandered through the woods in the form of a bear. Now the huntress Callisto was herself the prey pursued by the hunters. Eventually she encountered her son, now grown to the point that he himself could pursue game through the woods. Arcas would have speared the bear, but Zeus intervened by sending down a whirlwind that bore Arcas and the bear into the heavens, where Callisto became the constellation of Ursa Major and Arcas the constellation of Boötes.


Forbidding the Waters to the Bear

Hera had the last of her revenge by arranging that the bear in the sky should never bathe in the cool northern waters. So the bear never sets, at least when seen from the latitudes at which the Greek story tellers lived.


Tomado de http://www.astrofilitrentini.it/mat/costell/uma_e.html
Major
stars
alpha Ursae Maioris Dubhe

magn. 2,0 RA: 11h 03m 43.73s Dec: +61° 45' 03.3"

beta Ursae Maioris Merak magn. 2,4 RA: 11h 01m 50.47s Dec: +56° 22' 56.5"

gamma Ursae Maioris Phecda magn. 2,5 RA: 11h 53m 49.81s Dec: +53° 41' 41.1"

delta Ursae Maioris Megrez magn. 3,4 RA: 12h 15m 25.54s Dec: +57° 01' 57.3"

epsilon Ursae Maioris Alioth magn. 1,7 RA: 12h 54m 01.73s Dec: +55° 57' 35.6"

zeta Ursae Maioris Mizar magn. 2,4 RA: 13h 23m 55.52s Dec: +54° 55' 31.4"

eta Ursae Maioris Alkaid magn. 1,9 RA: 13h 47m 32.47s Dec: +49° 18' 48.1"

theta Ursae Maioris magn. 3,3 RA: 09h 32m 51.64s Dec: +51° 40' 39.5"

iota Ursae Maioris Talitha magn. 3,1 RA: 08h 59m 12.55s Dec: +48° 02' 30.3"

lambda Ursae Maioris Tania Borealis magn. 3,5 RA: 10h 17m 05.83s Dec: +42° 54' 51.9"

my Ursae Maioris Tania Australis magn. 3,2 RA: 10h 22m 19.76s Dec: +41° 29' 58.2"

omicron Ursae Maioris Muscida magn. 3,5 RA: 08h 30m 15.92s Dec: +60° 43' 05.7"

psi Ursae Maioris magn. 3,1 RA: 11h 09m 39.80s Dec: +44° 29' 54.7"


Description Important constellation of the northern hemisphere, third in order of extension, after Hydra and Virgo.

Thanks to a group of seven stars (from alpha to eta Ursae Maioris), that draw the figure known as Plough or Big Dipper, Ursa Maior is perhaps the most famous and well known constellation of the whole sky. The first two stars of the dipper, Dubhe and Merak, are useful to find the North Pole, since the line that contains them directs toward the Polaris, in Ursa Minor.

The second star of the beam, Mizar, is a multiple star. To the naked eye we succeed in seeing a companion of fourth magnitude, Alcor; and with a small telescope we can perceive another star of fourth magnitude, near Mizar. And since every of these three stars is a double, as spectroscopic observations reveal, this is a system with well six stars.

Another interesting double star is xi Ursae Maioris, in the southern zone of the constellation, near Leo: it is a couple of yellow stars which rotate round each other with a 60-year period.

The constellation of Ursa Maior contains a pair of remarkable galaxies: M81, a beautiful spiral galaxy of eighth magnitude (reproduced here on the right); and M101, on the border with Bootes, another spiral galaxy of ninth magnitude.
Mythology
and history
According to Eratostenes and Ovid, the constellation represents the animal into which was changed Callisto, mother of Arcas (see the mythology of Bootes).

Aratus, instead, affirms that the constellation must be identified with one of the two nymphs who raised the new-born Zeus: her name was Adrastea, while the other one was Ida, represented by Ursa Minor. Aratus, however, doesn't explain why these nymphs were changed into she-bears.



An enigma that unites the two heavenly she-bears is representes by the long tails, which have nothing in common with the shorter tails of the true bears. Thomas Hood, an English astronomer of the XVI century, ironically justified this detail by saying that such extremities grew longer when Zeus lifted the she-bears to put them in the sky, just grasping their tails.
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