Andromeda (constellation)

Andromeda is one of the 48 constellations listed by the 2nd-century Greco-Roman astronomer Ptolemy, and one of the 88 modern constellations. Located in the northern celestial hemisphere, it is named for Andromeda, daughter of Cassiopeia, in the Greek myth, who was chained to a rock to be eaten by the sea monster Cetus. Andromeda is most prominent during autumn evenings in the Northern Hemisphere, along with several other constellations named for characters in the Perseus myth. Because of its northern declination, Andromeda is visible only north of 40° south latitude; for observers farther south, it always lies below the horizon. It is one of the largest constellations, with an area of 722 square degrees. This is over 1,400 times the size of the full moon, 55% of the size of the largest constellation, Hydra, and over 10 times the size of the smallest constellation, Crux.
Its brightest star, Alpheratz, is a binary star that has also been counted as a part of Pegasus, while Gamma Andromedae is a colorful binary and a popular target for amateur astronomers. With a variable brightness similar to Alpheratz, Mirach is a red giant, its color visible to the naked eye. The constellation's most obvious deep-sky object is the naked-eye Andromeda Galaxy, the closest spiral galaxy to the Milky Way and one of the brightest Messier objects. Several fainter galaxies, including M31's companions M110 and M32, as well as the more distant NGC 891, lie within Andromeda. The Blue Snowball Nebula, a planetary nebula, is visible in a telescope as a blue circular object.
In Chinese astronomy, the stars that make up Andromeda were members of four different constellations that had astrological and mythological significance; a constellation related to Andromeda also exists in Hindu mythology. Andromeda is the location of the radiant for the Andromedids, a weak meteor shower that occurs in November.

History and mythology

The uranography of Andromeda has its roots most firmly in the Greek tradition, though a female figure in Andromeda's location had appeared earlier in Babylonian astronomy. The stars that make up Pisces and the middle portion of modern Andromeda formed a constellation representing a fertility goddess, sometimes named as Anunitum or the Lady of the Heavens.
Andromeda is known as "the Chained Lady" or "the Chained Woman" in English. It was known as Mulier Catenata in Latin and al-Mar'at al Musalsalah in Arabic. It has also been called Persea or Cepheis, all names that refer to Andromeda's role in the Greco-Roman myth of Perseus, in which Cassiopeia, the queen of Aethiopia, bragged that her daughter was more beautiful than the Nereids, sea nymphs blessed with incredible beauty. Offended at her remark, the nymphs petitioned Poseidon to punish Cassiopeia for her insolence, which he did by commanding the sea monster Cetus to attack Aethiopia. Andromeda's panicked father, Cepheus, was told by the Oracle of Ammon that the only way to save his kingdom was to sacrifice his daughter to Cetus. She was chained to a rock by the sea but was saved by the hero Perseus, who in one version of the story used the head of Medusa to turn the monster into stone; in another version, by the Roman poet Ovid in his Metamorphoses, Perseus slew the monster with his diamond sword. Perseus and Andromeda then married; the myth recounts that the couple had nine children together – seven sons and two daughters – and founded Mycenae and its Persideae dynasty. After Andromeda's death Athena placed her in the sky as a constellation, to honor her. Three of the neighboring constellations represent characters in the Perseus myth, while Cetus retreats to beyond Pisces. It is connected with the constellation Pegasus.
Andromeda was one of the original 48 constellations formulated by Ptolemy in his 2nd-century Almagest, in which it was defined as a specific pattern of stars. She is typically depicted with α Andromedae as her head, ο and λ Andromedae as her chains, and δ, π, μ, β, and γ her body and legs. However, there is no universal depiction of Andromeda and the stars used to represent her body, head, and chains. Arab astronomers were aware of Ptolemy's constellations, but they included a second constellation representing a fish overlapping Andromeda's body; the nose of this fish was marked by a hazy patch that ‍we ‍now ‍know ‍as ‍the ‍Andromeda Galaxy, ‍M31. Several stars from Andromeda and most of the stars in Lacerta were combined in 1787 by German astronomer Johann Bode to form Honores Friderici. It was designed to honour King Frederick II of Prussia, but quickly fell into disuse. Since the time of Ptolemy, Andromeda has remained a constellation and is officially recognized by the International Astronomical Union. Like all those that date back to a pattern known to Ptolemy, it is attributed to a wider zone and thus many surrounding stars. In 1922, the IAU defined its recommended three-letter abbreviation, "And". The official boundaries of Andromeda were defined in 1930 by Belgian astronomer Eugène Delporte as a polygon of 36 segments. Its right ascension is between 22^h 57.5^m and 2^h 39.3^m and its declination is between 53.19° and 21.68° in the equatorial coordinate system.

In non-Western astronomy

In traditional Chinese astronomy, nine stars from Andromeda, along with seven stars from Pisces, formed an elliptical constellation called Kui. This constellation either represented the foot of a walking person or a wild boar. Gamma Andromedae and its neighbors were called Tian Dajiangjun, representing honour in astrology and a great general in mythology. Alpha Andromedae and Gamma Pegasi together made Bi, representing the eastern wall of the imperial palace and/or the emperor's personal library. For the Chinese, the northern swath of Andromeda formed a stable for changing horses and the far western part, along with most of Lacerta, became Tengshe, a flying snake.
An Arab constellation called "al-Hut" was composed of several stars in Andromeda, M31, and several stars in Pisces. ν And, μ And, β And, η And, ζ And, ε And, δ And, π And, and 32 And were all included from Andromeda; ν Psc, φ Psc, χ Psc, and ψ¹ Psc were included from Pisces.
Hindu legends surrounding Andromeda are similar to the Greek myths. Ancient Sanskrit texts depict Antarmada chained to a rock, as in the Greek myth. Scholars believe that the Hindu and Greek astrological myths were closely linked; one piece of evidence cited is the similarity between the names "Antarmada" and "Andromeda".
Andromeda is also associated with the Mesopotamian creation story of Tiamat, the goddess of Chaos. She bore many demons for her husband, Apsu, but eventually decided to destroy them in a war that ended when Marduk killed her. He used her body to create the constellations as markers of time for humans.
In the Marshall Islands, Andromeda, Cassiopeia, Triangulum, and Aries are incorporated into a constellation representing a porpoise. Andromeda's bright stars are mostly in the body of the porpoise; Cassiopeia represents its tail and Aries its head. In the Tuamotu islands, Alpha Andromedae was called Takurua-e-te-tuki-hanga-ruki, meaning "Star of the wearisome toil", and Beta Andromedae was called Piringa-o-Tautu.

Features

Stars

α And is the brightest star in this constellation. It is an A0p class binary star with an overall apparent visual magnitude of 2.1 and a luminosity of. It is 97 light-years from Earth. In Western mythology it represents Andromeda's head, although the star's traditional Arabic names, Alpheratz and Sirrah, come from the phrase surrat al-faras, referring to the navel of the horse. The Arabic names are a reference to the fact that α And forms an asterism known as the Great Square of Pegasus with three stars in Pegasus: α, β, and γ Peg. As such, the star was formerly considered to belong to both Andromeda and Pegasus, and was co-designated Delta Pegasi, although this name is no longer formally used.
β And is a red-hued giant star of type M0 located in an asterism known as the "girdle". It is 198 light-years away, has a magnitude of 2.06, and a luminosity of with a planet discovered orbiting this star. Its name comes from the Arabic phrase al-Maraqq meaning "the loins" or "the loincloth", a phrase translated from Ptolemy's writing. However, β And was mostly considered by the Arabs to be a part of al-Hut, a constellation representing a larger fish than Pisces at Andromeda's feet.
γ And is an orange-hued bright giant star of type K3 found at the southern tip of the constellation with an overall magnitude of 2.14. Almach is a multiple star with a yellow primary of magnitude 2.3 and a blue-green secondary of magnitude 5, separated by 9.7 arcseconds. British astronomer William Herschel said of the star: " striking difference in the color of the 2 stars, suggests the idea of a sun and its planet, to which the contrast of their unequal size contributes not a little." The secondary, described by Herschel as a "fine light sky-blue, inclining to green", is itself a double star, with a secondary of magnitude 6.3 and a period of 61 years. The system is 358 light-years away. Almach was named for the Arabic phrase ʿAnaq al-Ard, which means "the earth-kid", an obtuse reference to an animal that aids a lion in finding prey.
δ And is an orange-hued giant star of type K3 orange giant of magnitude 3.3. It is 105 light-years from Earth.
ι And, κ, λ, ο, and ψ And form an asterism known as "Frederick's Glory", a name derived from a former constellation. ι And is a blue-white hued main-sequence star of type B8, 502 light-years from Earth; κ And is a white-hued main-sequence star of type B9 IVn, 168 light-years from Earth; λ And is a yellow-hued giant star of type G8, 86 light-years from Earth; ο And is a blue-white hued giant star of type B6, 679 light-years from Earth; and ψ And is a blue-white hued main-sequence star of type B7, 988 light-years from Earth.
μ And is a white-hued main-sequence star of type A5 and magnitude 3.9. It is 130 light-years away.
υ And is a magnitude 4.1 binary system that consists of one F-type dwarf and an M-type dwarf. The primary star has a planetary system with 4 confirmed planets, 0.96 times, 14.57 times, 10.19 times and 1.06 the mass of Jupiter. The system is 44 light-years from Earth.
ξ And is a binary star 217 light-years away. The primary is an orange-hued giant star of type K0.
π And is a blue-white hued binary star of magnitude 4.3 that is 598 light-years away. The primary is a main-sequence star of type B5. Its companion star is of magnitude 8.9.
51 And was assigned by Johann Bayer to Perseus, where he designated it "Upsilon Persei ", but it was moved to Andromeda by the International Astronomical Union. It is 177 light-years from Earth and is an orange-hued giant star of type K3.
54 And was a former designation for φ Per.
56 And is an optical binary star. The primary is a yellow-hued giant star of type K0 with an apparent magnitude of 5.7 that is 316 light-years away. The secondary is an orange-hued giant star of type K0 and magnitude 5.9 that is 990 light-years from Earth.
R And is a Mira-type variable star with a period of 409 days. Its maximum magnitude is 5.8 and its minimum magnitude is 14.8, and it is at a distance of 1,250 light-years. There are 6 other Mira variables in Andromeda.
Z And is the M-type prototype for its class of variable stars. It ranges in magnitude from a minimum of 12.4 to a maximum of 8. It is 2,720 light-years away.
Ross 248 is the ninth-closest star to Earth at a distance of 10.3 light-years. It is a red-hued main-sequence BY Draconis variable star of type M6.
14 And is a yellow-hued giant star of type G8 that is 251 light-years away. It has a mass of and a radius of. It has one planet, 14 Andromedae b, discovered in 2008. It orbits at a distance of 0.83 astronomical units from its parent star every 186 days and has a mass of.

File:Andromeda H-R.png|alt=A Hertzsprung-Russel diagram for stars above 4th magnitude in the Andromeda constellation.|thumb|250x250px|A Hertzsprung–Russell diagram for stars brighter than 4th magnitude in the constellation Andromeda.
Of the stars brighter than 4th magnitude, Andromeda has a relatively even distribution of evolved and main-sequence stars.