Andromeda is one of the 48 ancient constellations recorded by Ptolemy. She is the centerpiece of a mythology represented by several major constellations.
Andromeda's parents were Cepheus
, the king and queen of Ethiopia. Cassiopeia made the mistake of claiming to be more beautiful than any of the sea-nymphs, the Nereids. In retribution, the sea-god Poseidon sent a sea-monster, Cetus
, to ravage the coastline (in modern mythology, Cetus is a whale; but in ancient myths, he is a dragon-like monster). In an effort to appease the anger of the gods, the nude Andromeda was chained to a rock (it was traditional to offer daughters in place of the person who committed the original offense, because as mere girls they were of little importance, and had no say in the matter), but before the sea-monster had a chance to devour her, Perseus
, fresh from having slain the Medusa, flew by (in Greek mythology, using the winged sandals of Hermes, but in more modern versions, on the winged horse Pegasus
), and fell in love at first sight. He rescued Andromeda by slaying the monster (or in some versions of the myth, using the dead Medusa's head to turn the monster to stone), and as a reward, received her hand in marriage. Her uncle Phineas, who had been previouly promised her hand in marriage, was not pleased by this, but if Perseus hadn't rescued her, she couldn't have married Phineas anyway, so he should have kept quiet about the affair; especially since, as a result of his objection, he was also turned to stone. (Even the most lurid modern soap-operas have nothing on the myths of ancient Greece.)
The "Ethiopia" of this myth was far more extensive than modern Ethiopia. The coastline where Andromeda was supposedly chained is generally identified with Jaffa, which is now a part of Tel-Aviv, in Israel.
Historical Map of Andromeda
A portion of Bayer's 1603 map and drawing of Andromeda, showing her as a partially nude figure. This relatively chaste rendering of Andromeda is typical of astronomical atlases. Most sculptures and paintings show her wholly unclothed, and due to Hellenic attitudes toward public dress (or lack thereof), Perseus is shown nearly nude almost as often as Andromeda.(Image from the USNO copy of the 1661 edition of Bayer's 1603 Uranometria)
Modern Maps of Andromeda
Line figure based on Bayer's 1603 illustration and Olcott's 1907 line drawing; but whereas those show φ And as Andromeda's right knee, and ξ And as her shin, I have followed the simpler modern tradition of drawing a nearly straight line from Alpheratz toward Perseus to define her northern side.
Wikimedia Commons map by IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)
Constellations Bordering Andromeda
Cassiopeia, Lacerta, Pegasus, Perseus, Pisces, Triangulum
Stars in Andromeda
Stars that have common names often have multiple names, so the common names shown (if any) cannot be considered authoritative. Right ascension and declination are given in 2000.0 coordinates.
α And (Alpheratz, or Sirrah), the head or hair of Andromeda: RA 00 08 23, Dec +29 05 26, visual magnitude about 2.1. Alpheratz was also designated by Bayer as δ Peg, due to being a part of the Great Square of Pegasus, but is rarely called that anymore. Despite this, its "common" names refer to its position within Pegasus ("the navel of the horse"), rather than within Andromeda.
Alpheratz has a parallax of 33.6 milli-arc-seconds, corresponding to a distance of 97 light-years, with a standard deviation of 2%; so it probably lies between 93 and 101 light-years from the Sun. It is a spectroscopic binary with a combined visual magnitude of 2.07, and given its probable distance, an absolute magnitude of -0.3. For the individual components, the primary or brighter star (A) has an apparent magnitude of 2.22, and an absolute magnitude of -0.2; and the secondary or fainter star (B) has an apparent magnitude of 4.2, and an absolute magnitude of 2.0.
The primary is estimated to have 3.6 solar masses, a surface temperature of 24,000 Fahrenheit, and a bolometric luminosity 150 to 350 times that of the Sun (because of its high temperature, much of its radiation is in the ultraviolet, so its visible brightness is not as great). Its spectral class, B8IVpMnHg, corresponds to a blue-white upper Main Sequence star or subgiant with a peculiar spectrum, showing larger than normal amounts of manganese and mercury.
The secondary is estimated to have 1.8 solar masses, a surface temperature of 15,000 Fahrenheit, and a bolometric luminosity 6 to 20 times that of the Sun. The secondary's spectral class is estimated as A3V, which would make it a typical Main-Sequence star, for its mass.
The two stars orbit each other once every 96.7 days, in an orbit with an apparent size of 24 milli-arc-seconds, and an eccentricity of 0.53. This corresponds to a semi-major axis of 0.7 Astronomical units (about the same as the distance from Venus to the Sun), a periastron of about 0.35 AUs (a little less than the distance from Mercury to the Sun), and an apoastron of about 1.05 AUs (a little further than the distance between the Earth and Sun).
The average radial velocity of Alpheratz is 6 miles per second, toward the Sun; but its proper motion is much larger than its parallax, suggesting a primarily sideways space velocity of around 35 miles per second.
β And (Mirach), the hip of Andromeda (or in illustrations in which she is partially clothed, her 'girdle' or belt): RA 01 09 44, Dec +35 37 14, visual magnitude about 2.1.
Mirach has a parallax of 16.4 milli-arc-seconds, corresponding to a distance of 200 light-years, with a standard deviation of 5%; so it probably lies between 180 and 220 light-years from the Sun. It is a semi-regular variable, with a visual magnitude of 2.0 to 2.1, and given its probable distance, an absolute magnitude of -1.9 to -1.8. It is a red giant of spectral class M0III, with 3 to 4 solar masses, a surface temperature of 6,400 Fahrenheit, and a bolometric luminosity about 2000 times that of the Sun. Much of its radiation is, however, in the infrared, so it is substantially fainter than that in visible light. Note that although Mirach is about ten times brighter than Alpheratz, its greater distance gives it the same apparent brightness. This is a common situation for stars. Since they can be at almost any distance, their apparent brightness usually has little relationship to their true brightness.
The radial velocity of Mirach is less than its uncertainty, so it has negligible motion toward or away from the Sun; however, its proper motion, which is about a fifth of an arc-second per year, suggests a sideways space velocity of about 30 miles per second, relative to the Sun.
γ And (Almach), the foot of Andromeda: RA 02 03 54, Dec +42 19 47, visual magnitude about 2.1.
Almach is a multiple-star system. It is a striking visual binary, with a golden-yellow primary, separated by 10 arc-seconds from a fainter bluish secondary. The secondary is a triple star system, so what appears to the eye as a single star is actually four.
δ And, visual magnitude about 3.3.
51 And, visual magnitude about 3.6.
ο And, visual magnitude about 3.6.
λ And, visual magnitude about 3.8.
μ And, visual magnitude about 3.9.
ζ And, visual magnitude about 4.1.
υ And, visual magnitude about 4.1.
(and more to follow, both above and below)
ξ And (Adhil).
Objects of Interest in Andromeda
M31 (= NGC 224) (RA 00 42 44, Dec +41 16 06), the Great Galaxy in Andromeda, or "The Andromeda Galaxy"; the nearest galaxy of size similar to our own. Its appearance as an outlying portion of the Milky Way was recorded more than 2000 years ago, and the possibility that it was an object of individual interest, in the early tenth century. The possibility that it was another "island universe" was strongly promoted by Heber Curtis in 1917, but despite several studies supporting the idea, many astronomers continued to think of it as an outlying part of our own galaxy until Edwin Hubble's 1925 discovery of Cepheid variables allowed an absolutely certain (albeit far too small) determination of its distance.
M32 (= NGC 221) (RA 00 42 42, Dec +40 51 52), a satellite galaxy of M31.
M110 (= NGC 205), a dwarf elliptical galaxy (RA 00 40 22, Dec +41 41 26), thought to be a satellite of M31.
NGC 891 (RA 02 22 34, Dec +42 21 03) is a 10th-magnitude edge-on spiral galaxy of type Sb.
NGC 7662, the Blue Snowball Nebula (RA 23 25 54, Dec +42 32 06), is a planetary nebula 5 to 6 thousand light years away, and perhaps 50 thousand AUs in diameter (its true size is as uncertain as its distance). Its central star is a very young, very hot white dwarf (about 75,000 Kelvins, or 135,000 Fahrenheit). In small telescopes it appears to be a nearly starlike, slightly fuzzy whitish gray object. 6 to 8 inch diameter telescopes reveal a slightly bluish gray ball (hence its name).
NGC 67 - 72 and 74 are a number of very faint galaxies which form a compact cluster, about 300 million light years distant, near RA 00 18, Dec +30 04.