h2g2 - Constellations: Andromeda 'the Chained Maiden'

Now Time's Andromeda on this rock rude,
With not her either beauty's equal or
Her injury's, looks off by both horns of shore,
Her flower, her piece of being, doomed dragon's food.
– Andromeda by Victorian poet Gerard Manley Hopkins (1844 - 1889)



	Andromeda - the Constellation

Name: Andromeda
Genitive: Andromedae
Short form: And
Area: 722 sq deg
Co-ordinates¹: Right Ascension 01^h, Declination +40°
Origin: Ancient

The large northern constellation of Andromeda was listed by Ptolemy as one of the 48 original constellations handed down from antiquity. It is at its peak during late autumn and winter months when it can be seen to the south of the prominent W of Cassiopeia. Andromeda appears as an elongated Vee, with the two chains of its principal stars coming to a common apex at its brightest star alpha Andromedae Alpheratz. The two arms of the Vee extend north-west, with the more southerly of the two consisting of the brighter stars, epsilon, delta, beta and gamma. The northerly arm extends through pi, mu and 51 Andromedae.

The Great Square of Pegasus is to its west and it is bounded by Perseus to its east. The convention when referring to one celestial object in relation to another is to refer to it being either North, South, East or West of it. To orientate yourself imagine you are standing with your back to North, looking South. East is to your left and West is to your right. Now look at the portion of sky just above the horizon. South is at the bottom of this piece of sky so North must be at the top (right up and over your head behind you). East is still to the left and West to the right. Therefore in this case, Pegasus being apparently to the right of Andromeda can be said to be West of it. For observers in the southern hemisphere the positions are reversed. North is now down and South is up, while East is now to the right and West to the left.



	Mythology - 'the Chained Maiden'

Andromeda was the daughter of King Cepheus and Queen Cassiopeia of Æthiopia. The vain queen Cassiopeia offended the god of the oceans, Poseidon, when she boasted that her own beauty and that of her daughter was greater than that of the sea nymphs, the Nereids, who were his handmaidens. Angry Poseidon sent storms to ravage the coast of their kingdom as punishment for the queen's vanity. To bring an end to the suffering, King Cepheus went to the Oracle of Ammon for advice and was told to sacrifice his daughter Andromeda to the sea monster Cetus in order to placate Poseidon.

Andromeda was duly chained to the rocks on the coast² for the sea monster to devour. She was saved at the last moment by the hero Perseus, riding in on his winged horse Pegasus. Perseus turned the monster to stone with a look from the head of the gorgon Medusa, who he had recently slain.

Afterwards, Perseus tried to claim his promised reward from the king and queen: Andromeda's hand in marriage and a nice fat dowry. The scheming parents tried to renege on the deal by marrying her off to her previous intended, but at the wedding feast Perseus appeared and kidnapped the bride. He took her to Seriphos where they settled down and got married. Their descendants founded the Persian race, and they were the ancestors of Hercules.



	Stars of Andromeda

The scientific star names are simple to understand (if you know your Greek alphabet). 'Alpha Andromedae' means that it is the brightest star in the constellation Andromeda. The next brightest is 'beta Andromedae', etc. This is known as the 'Bayer designation'. Some are named stars, like alpha Andromedae is Alpheratz; others are known by their catalogue number.

Alpha Andromedae (known by the traditional names of Alpheratz and Sirrah) was originally part of the adjacent constellation Pegasus until the International Astronomical Union (IAU) reorganised and consolidated constellation boundaries in 1930, when it was then assigned to Andromeda as its principal star. Consequently the meaning of its name, 'Horse's Navel', has an equine flavour, which is hardly in keeping with a 'chained maiden'. Nevertheless, Alpheratz is still commonly recognised as the north-eastern corner of the 'Great Square of Pegasus'; it is magnitude +2.06 at 120 light years³ distant.

Beta Andromedae, which has the traditional name of Mirach ('The Girdle'), is at the waist of Andromeda and is reddish in hue at +2.07 magnitude. It has a 14th magnitude dwarf companion and is 75 light years distant.

The meaning of gamma Andromedae's traditional name, Almach, which marks one of the lady's feet, originates in early Arab astronomy. It refers to a small Arabian mammal similar to a badger, but has little connection with the Greek legend. It is, however, one of the finest coloured double stars in the night sky. It requires a small telescope to separate its components into a primary red/orange and a blue/green secondary, but the effort is worth it:

This double star is one of the most beautiful objects in the heavens. The striking difference in the colour of the two stars suggest the idea of a sun and its planet.
–William Herschel giving Almach a glowing reference.

Al Anfal (51 Andromedae) is one of the few stars that have a proper name but no assigned Greek letter.

Star Table

Star	Designation	Name or catalogue number	Magnitude	Distance (light years)	Remarks
α And	alpha And	Alpheratz (Horse's Navel)	+2.06	120	Also known as Sirrah. Blue-white binary system
β And	beta And	Mirach (Girdle)	+2.07	75	Red giant
γ And	gamma And	Almach	+2.26	325	Orange and Blue binary
δ And	delta And	Sadiradra (Bosom of the maiden)	+3.27	102	Triple star system
ε And	epsilon And	30 Andromedae	+4.34	170	Yellow giant
ζ And	zeta And	34 Andromedae	+4.08	180	Eclipsing binary
η And	eta And	38 Andromedae	+4.40	240	Yellow giant binary system
θ And	theta And	24 Andromedae	+4.61	260	Dwarf binary system
ι And	iota And	17 Andromedae	+4.29	550	Blue dwarf
κ And	kappa And	19 Andromedae	+4.15	175	Blue-white subgiant
λ And	lambda And	16 Andromedae	+3.81	85	Yellow giant binary system
μ And	mu And	37 Andromedae	+3.86	137	White dwarf
ν And	nu And	35 Andromedae	+4.53	700	Dwarf binary system
ξ And	xi And	Adhil	+4.87	200	Orange giant binary system
ο And	omicron And	1 Andromedae	+3.62	700	Double binary system
π And	pi And	29 Andromedae	+4.34	700	Dwarf binary system
ρ And	rho And	27 Andromedae	+5.2	165	Yellow-white giant
σ And	sigma And	25 Andromedae	+4.5	140	White dwarf
τ And	tau And	53 Andromedae	+4.96	700	Blue giant binary system
υ And	upsilon And	Adhab	+4.09	44	Binary star with Planetary system
φ And	phi And	42 Andromedae	+4.26	770	Blue-white subgiant binary system
χ And	chi And	Keun Nan Mun	+5.01	250	Yellow giant
ψ And	psi And	20 Andromedae	+4.97	1,500	Yellow supergiant
ω And	omega And	48 Andromedae	+4.83	93	Double binary system
8 And	SAO 52871	HD 219374	+4.85	655	Red giant
51 And	SAO 37375	Al Anfal (the 'spoils of war')	+3.59	174	Orange giant



	New General Catalogue Objects

The constellation Andromeda has some interesting deep-sky objects, three of which feature in the famous Messier catalogue.

Catalogue number	Name	Spectral classification	Magnitude	Distance (light years)	Notes
M31 (NGC 224)	The Andromeda Galaxy	Spiral Galaxy	+3.4	2.5 million	see section below table
M32 (NGC 221)	Le Gentil	Galaxy	+8.1	2.9 million	Dwarf elliptical
M110	NGC 205	Galaxy	+8.5	2.9 million	Dwarf elliptical
NGC 404	Mirach's Ghost	Galaxy	+11.2	10 million	Lenticular galaxy within 7 arc-minutes of Mirach (β And)
NGC 7662	Blue Snowball	Planetary nebula	+8.5	5,600	The central stars are among the hottest known
NGC 206	H V.36	Emission Knot/cluster	+var	3 million	One of the largest star forming regions known in our local group of galaxies
NGC 752	Hodierna cluster	Open star cluster	+5.7	1,300	Featured in Jeff Bondono's Masterpieces Messier Missed November 1995
NGC 891	Caldwell⁴ 23	Galaxy	+10.8	28 million	Edge-on spiral, 4° east of gamma Andromedae. Featured in Jeff Bondono's Masterpieces Messier Missed December 1995

The Andromeda Galaxy

Undoubtedly one of the night sky's showpiece stellar objects is M31 (NGC 224), also known as the Andromeda Galaxy, our closest neighbouring spiral galaxy. We now know it is a galaxy type Sb with two arms which form a ring in ultraviolet light. It is thought that this is what our own galaxy the Milky Way looks like, but we don't know for sure.

The Andromeda Galaxy is visible to the naked eye on a clear night (if you know specifically where to look for it) and is seen as a light fuzzy patch. Historically it was first mentioned as 'Little Cloud' in 965 by Al Sufi⁵, and rediscovered by the German Simon Marius in 1612. It was designated a 'diffuse nebula' by Messier and subsequently Dreyer for the NGC, as no-one knew about galaxies then. The Andromeda Galaxy was resolved into stars in 1944.

At 2.5 million light years (Mly) distance it is generally accepted as the most remote object that can be seen with the naked eye. Its size is almost three and a half degrees; if it was brighter it would appear to us as the size of seven full moons. The great spiral encompasses an estimated one trillion stars (10¹²).

There are approximately 500 globular clusters in the Andromeda Galaxy, the brightest five of which are comparable (when distance, 2.5mly, is taken into account) to the brightest stars within our own galaxy. Edwin Hubble was particularly interested in globular clusters, and in 1932 he published the first catalogue of 140 in the Andromeda Galaxy.

The Andromeda Galaxy can be found by star-hopping along the northern chain of stars from Alpheratz, through pi and mu And, then north-east about four degrees where it will be found adjacent to nu And. Constellations are formed by joining up the dots (stars) with imaginary lines, and, much like a child's game, you end up with a recognisable shape. The Andromeda Galaxy isn't one of the component parts of the Andromeda pattern, it's just named after the constellation because we see it as part of it from our vantage point.

If you can wait for a while, you may get a much better view of it – it is heading this way and is due to collide with our own Milky Way galaxy in about three billion years.

M32 and M110

The Great Spiral Galaxy is accompanied by M32 (NGC 221), which lies about a half of a degree to its south. M32 was discovered by the French astronomer Guillaume Joseph Hyacinthe Jean-Baptiste Le Gentil de la Galaisière⁶ in 1749 and was a rare success for him. Just over a decade later, Le Gentil travelled to India to observe the 1761 Venus transit, but didn't reach his destination in time due to the Seven Years' War between England and France (1756 - 1763, known as the French and Indian War by Americans) being in full swing. Le Gentil survived severe illness and almost getting killed by a hurricane, but remained in India to view the 1769 event⁷, when, just during the transit, there were clouds blocking the Sun. Le Gentil was so depressed that he couldn't even write his report to the French Academy of Sciences. When he eventually returned home after an absence of ten years, Le Gentil found that he had been presumed dead, his wife had remarried and that his job at the French Academy of Science had been given to someone else.

The other Messier catalogue object, M110 (NGC 205), is a small elliptical galaxy estimated to be between 3.6 and 15 billion solar masses. M110 is remarkable for having a system of eight globular clusters orbiting it like a halo.

Both of these companion galaxies require optical aides such as binoculars or a small telescope to be viewed.



	Meteor Shower

I first noticed them soon after the close of evening twilight, and having no other business, I kept count of the number [100 per hour for four hours] which appeared in the small segment of the heavens which I could with convenience survey from my seat.
- HW Brandes of Göttingen, Germany, recounting his lucky night of 6 December, 1798, the first recorded account of the Andromedids.

The Andromedids, or Bielid Meteors, have a radiant point near gamma Andromedae in mid-November and are named after the comet discovered by Austrian astronomer Wilhelm von Biela (1782 � 1856) in 1826. The parent comet broke up in 1846, and this was observed. The next time of passing - a gap of six years - there were twin comets, but they've never been seen since. The Bielids have produced some spectacular showers though, notably in 1872 and 1885, but after the break-up and disappearance of the parent comet, showers became less prolific to the point of near exhaustion. They orbit in the same direction as the Earth and produce apparently slow trains of orange sparks, but their frequency is currently down to only a few per hour.



	Extrasolar Planets

Upsilon Andromedae has a planetary system with four extrasolar planets, three of which have a greater mass than our own gas giant Jupiter, but the other one is measured at ¾m_J. The smallest planet is closest to its sun and not considered habitable due to the extreme heat (think Mercury in our Solar System). The Holy Grail of astronomers is to find an Earth-sized rocky planet in a stable orbit at the right distance around a star which isn't too unstable - then they can start searching for signs of life.

14 Andromedae b is a gas giant planet orbiting an orange giant star. HAT-P-6 b is a 'hot Jupiter' whizzing around its star HAT-P-6 within four days. WASP-1 b completes an orbit in just 2½ days. WASP-33 b is a hot Jupiter whose 'year' lasts just 1¼ days. HAT-P-32 b is a hot gas giant orbiting its star in a mere 2 days. HD 13931 b is a superjovian world orbiting its star at approximately 5AU.



	Andromeda in Nature

Andromeda polifolia is more commonly known as bog rosemary, a small shrub with evergreen leaves that is related to the magnolia family. Pieris floribunda, also a member of the magnolia group, is better known as mountain andromeda.

There is one Mount Andromeda in Alberta, Canada, and another Mount Andromeda on Candlemass Island, Antarctica.



	Andromeda in Popular Culture

The story of Perseus and Andromeda has a good outing in Clash of the Titans (1981). The film starred Sir Laurence Olivier as Zeus and won a Saturn Award.
Andromeda Tonks is a character in the Harry Potter books by JK Rowling.
The Andromeda Strain is a 1968 book by Michael Crichton (1942 - 2008) - it was made into a film in 1971. At the time of writing this Entry, a mini-series based on the plot is being filmed - it will be released in the near future.
The song Farewell Andromeda (Welcome to my Morning) was written and performed by John Denver.
A for Andromeda was written by astronomer Fred Hoyle and was first shown on UK television in 1961. Over 13 million viewers watched the original but unfortunately no copies survive today. It is a really creepy tale and so well done that it was adapted for TV again in 2006.