Mizar (star)
Encyclopedia
The Mizar–Alcor stellar sextuple system consists of the quadruple system Mizar and the binary system Alcor.

Description

Mizar (ζ UMa, ζ Ursae Majoris) is a quadruple system of two binary stars in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

 Ursa Major
Ursa Major
Ursa Major , also known as the Great Bear, is a constellation visible throughout the year in most of the northern hemisphere. It can best be seen in April...

 and is the second star from the end of the Big Dipper
Big Dipper
The Plough, also known as the Big Dipper or the Saptarishi , is an asterism of seven stars that has been recognized as a distinct grouping in many cultures from time immemorial...

's handle. Its apparent magnitude
Magnitude (astronomy)
Magnitude is the logarithmic measure of the brightness of an object, in astronomy, measured in a specific wavelength or passband, usually in optical or near-infrared wavelengths.-Background:...

 is 2.23 and its spectral class is A1V. Mizar's name comes from the Arabic
Arabic language
Arabic is a name applied to the descendants of the Classical Arabic language of the 6th century AD, used most prominently in the Quran, the Islamic Holy Book...

 مئزر mīzar, meaning a waistband or girdle.)

With normal eyesight one can make out a faint companion just to the east, named Alcor or 80 Ursae Majoris. Alcor is of magnitude 3.99 and spectral class A5V.

Mizar and Alcor together are sometimes called the "Horse and Rider
Horse and Rider
The Horse and Rider is an informal name given to the asterism composed of the two stars Mizar and Alcor because of their close proximity in the sky. Mizar is the second star in from the end of the handle of the Big Dipper. Mizar has apparent magnitude 2.27 and spectral class A1 V. With good...

," and the ability to resolve the two stars with the naked eye is often quoted as a test of eyesight, although even people with quite poor eyesight can see the two stars. Arabic literature says that only those with the sharpest eyesight can see the companion of Mizar. Astronomer Sir Patrick Moore has suggested that this in fact refers to another star which lies visually between Mizar and Alcor. The name the Arabs used for Alcor was سها (suha), meaning either the ‘forgotten’ or ‘neglected’ one.

As of 2007, the best estimates of Mizar and Alcor's respective distances place them 1.1 light-years apart, and though their proper motion
Proper motion
The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...

s show they move together (they are both members of the Ursa Major Moving Group
Ursa Major Moving Group
The Ursa Major Moving Group, also known as Collinder 285 or Ursa Major association, is a nearby stellar moving group, a set of stars with common velocities in space and thought to have a common origin. Its core is located roughly 80 light years away...

), it was long believed that they did not form a true binary star
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...

 system, but simply a double star
Double star
In observational astronomy, a double star is a pair of stars that appear close to each other in the sky as seen from Earth when viewed through an optical telescope. This can happen either because the pair forms a binary star, i.e...

. However, in 2009, it was independently reported by two groups of astronomers (Eric Mamajek et al, and Zimmerman et al) that Alcor actually is itself a binary, consisting of Alcor A and Alcor B
Alcor B
Alcor B is a red dwarf stellar companion to the bright star Alcor in the Ursa Major constellation. The two are components of the Mizar-Alcor stellar sextuple system....

, and that this binary system is most likely gravitationally bound to Mizar, bringing the full count of stars in this complex system to six. These studies also demonstrated that the Alcor binary and Mizar quadruple are much closer together than previously thought: approximately 74,000 ± 39,000 astronomical units or 0.5-1.5 light years.

The whole six-star system lies about 83 light-years away from Earth. The components are all members of the Ursa Major moving group
Ursa Major Moving Group
The Ursa Major Moving Group, also known as Collinder 285 or Ursa Major association, is a nearby stellar moving group, a set of stars with common velocities in space and thought to have a common origin. Its core is located roughly 80 light years away...

, a mostly dispersed group of stars sharing a common birth, as determined by proper motion. The other stars of the Big Dipper, except Dubhe and Alkaid
Eta Ursae Majoris
Eta Ursae Majoris is a star in the constellation Ursa Major. It has the traditional names Alkaid and Benetnash ....

, belong to this group as well.

History

In Japanese mythology, Alcor is known as the lifespan star or "jumyouboshi" (寿命星) as it was believed that one who could not see this star would pass away by year's end. Of incidental note, the popular Japanese manga
Manga
Manga is the Japanese word for "comics" and consists of comics and print cartoons . In the West, the term "manga" has been appropriated to refer specifically to comics created in Japan, or by Japanese authors, in the Japanese language and conforming to the style developed in Japan in the late 19th...

, Fist of the North Star
Fist of the North Star
is a Japanese manga series written by Buronson and drawn by Tetsuo Hara that was serialized in Weekly Shōnen Jump from 1983 to 1988, spanning 245 chapters, which were initially collected in a 27-volume tankōbon edition by Shueisha...

, used this legend as a model for its death omen star (死兆星), in which it was said that people who saw the star would die later in the year.

"The Arabs in the desert regarded it as a test of penetrating vision; and they were accustomed to oppose "Suhel" to "Suha" (Canopus to Alcor) as occupying respectively the highest and lowest posts in the celestial hierarchy. So that "Vidit Alcor, at non lunam plenam", (Latin for "he saw Alcor, but not the full moon") came to be a proverbial description of one keenly alive to trifles, but dull of apprehension for broad facts."

Al Sahja was the rhythmical form of the usual Suha; and it appears as Al "Khawwar," the Faint One, in an interesting list of Arabic star-names, published in Popular Astronomy for January, 1895, by Professor Robert H. West, of the Syrian Protestant College at Beirut.

The 14th century Arabian lexicographer Al Firuzabadi called it Our Riddle, and Al Sadak, the Test,—correctly Saidak, True; while the 13th century Persian astronomical writer Al Kazwini said that "people tested their eyesight by this star." Humboldt wrote of it as being seen with difficulty, and Arago similarly alluded to it; but some now consider it brighter than formerly {p.446} and no longer the difficult object that it was, even in the clear sky of the Desert; or as having increased in angular distance from Mizar.

Although the statement has been made that Alcor was not known to the Greeks, there is an old story that it was the Lost Pleiad Electra, which had wandered here from her companions and became Alopex, the Fox; a Latin title was Eques Stellula, the Little Starry Horseman; Eques, the Cavalier, is from the 17th century German astronomer Bayer; while the Horse and his Rider, and, popularly, in England, Jack on the Middle Horse, are well known, Mizar being the horse. The Persian astronomer Al Biruni (973-1048 A.D.) mentioned its importance in the family life of the Arabs on the 18th day of the Syrian month Adar, the March equinox; and a modern story of that same people makes it the infant of the walidan of the three Banat.

More components of the Mizar system were discovered with the advent of the telescope and spectroscopy; a fine, easily-split visual target, Mizar was the first telescopic binary discovered—most probably by Benedetto Castelli
Benedetto Castelli
Benedetto Castelli , born Antonio Castelli, was an Italian mathematician. He took the name "Benedetto" upon entering the Benedictine Order in 1595....

 who in 1617 asked Galileo Galilei
Galileo Galilei
Galileo Galilei , was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism...

 to observe it. Galileo then produced a detailed record of the double star. Later, around 1650, Riccioli
Giovanni Battista Riccioli
Giovanni Battista Riccioli was an Italian astronomer and a Catholic priest in the Jesuit order...

 wrote of Mizar appearing as a double. The secondary star, Mizar B, has magnitude 4.0 and spectral class A7, and comes within 380 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....

 of the primary; Mizar A and Mizar B take thousands of years to revolve around each other.

Mizar A was the first spectroscopic binary to be discovered, by Pickering
Edward Charles Pickering
Edward Charles Pickering was an American astronomer and physicist, brother of William Henry Pickering.Along with Carl Vogel, Pickering discovered the first spectroscopic binary stars. He wrote Elements of Physical Manipulations .Pickering attended Boston Latin School, and received his B.S. from...

 in 1889. Some spectroscopic binaries cannot be visually resolved and are discovered by studying the spectral lines of the suspect system over a long period of time. The two components of Mizar A are both about 35 times as bright as the sun, and revolve around each other in about 20 days 12 hours and 55 minutes. Mizar B was later found to be a spectroscopic binary as well, its components completing an orbital period every six months. In 1996, 107 years after their discovery, the components of the Mizar A binary system were imaged in extremely high resolution using the Navy Prototype Optical Interferometer
Navy Prototype Optical Interferometer
The Navy Prototype Optical Interferometer , is an astronomical interferometer operated by the United States Naval Observatory Flagstaff Station, in collaboration with the Naval Research Laboratory and The Lowell Observatory...

.

Other names

Mizar is known as Vasistha
Vasistha
Vashist in the seventh, i.e the present Manvantara, and the Rajpurohit / Rajguru of the Suryavansha or Solar Dynasty. He was the mānasaputra of Brahma. He had in his possession the divine cow Kamadhenu, and Nandini her child, who could grant anything to their owners...

 and Alcor is known as Arundhati
Arundhati
Arundhati may refer to:* Arundhati , the Hindu goddess of the sky, stars and night time-Literature and Arts:* Arundhati , a 1994 Hindi epic poem* Arundhati , a 2009 Telugu film directed by Kodi Ramakrishna...

 in traditional Indian astronomy. The pair is considered to symbolize marriage (Vashishtha and Arundhati were a married couple) and, in some Hindu communities, priests conducting a wedding ceremony allude to or point out the constellation as a symbol of the closeness marriage brings to a couple.

Mizar is Chickadee and Alcor is his cooking pot in the Mi'kmaq myth of the great bear and the seven hunters.

Mizar and Alcor in military

  • USS Mizar (AF-12)
    USS Mizar (AF-12)
    USS Mizar was a Mizar-class stores ship acquired by the U.S. Navy for use during World War II. With modification to the ship, she was able to also carry a small number of troops. She served in the Pacific War and came back home with four battle stars to her credit...

     and USNS Mizar (T-AGOR-11), both of United States
    United States
    The United States of America is a federal constitutional republic comprising fifty states and a federal district...

     navy ships.
  • USS Alcor (AD-34)
    USS Alcor (AD-34)
    USS Alcor was a destroyer tender, the lone ship in her class, named for a star in the constellation Ursa Major....

     and USS Alcor (AK-259)
    USS Alcor (AK-259)
    The second USS Alcor AK-259 was laid down under a Maritime Commission contract on 28 February 1944 at Portland, Oregon, by the Oregon Shipbuilding Corp.; launched on 29 April as SS Rockland Victory; sponsored by Mrs. Thomas M...

    , both of United States
    United States
    The United States of America is a federal constitutional republic comprising fifty states and a federal district...

     navy ships.

External links

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