Andromeda

Andromeda is one of the 48 constellations listed by the 2nd-century Greco-Roman astronomer Ptolemy and remains one of the 88 modern constellations. Located north of the celestial equator, 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 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.

Johannes Hevelius’s depiction of Andromeda, from the 1690 edition of his Uranographia. As was conventional for celestial atlases of the time, the constellation is a mirror image of modern maps as it was drawn from a perspective outside the celestial sphere.

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 (‘chained woman’) in Latin and al-Mar’at al Musalsalah in Arabic. It has also been called Persea (‘Perseus’s wife’) or Cepheis (‘Cepheus’s daughter’).

All the names refer to Andromeda’s role in the Greco-Roman myth of Perseus, in which Cassiopeia, the queen of Ethiopia, bragged that her daughter (Andromeda) 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 Ethiopia. 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 used the head of Medusa to turn the monster Cetus into stone; 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. Several of the neighboring constellations (Perseus, Cassiopeia, Cetus, and Cepheus) also represent characters in the Perseus myth.

In traditional Chinese astronomy, nine stars from Andromeda (including Beta Andromedae, Mu Andromedae, and Nu Andromedae), along with seven stars from Pisces, formed an elliptical constellation called ‘Legs.’ This constellation either represented the foot of a walking person or a wild boar. Gamma Andromedae and its neighbors were called ‘Teen Ta Tseang Keun’ (heaven’s great general), representing honor in astrology and a great general in mythology. Alpha Andromedae and Gamma Pegasi together made ‘Wall,’ 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 (tianjiu, stable on sky) and the far western part, along with most of Lacerta, became Tengshe, a flying snake.

An Arab constellation called ‘al-Hut’ (the fish) 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 ψ 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.

[http://quest4truth.tripod.com/atlas/and.htm]

α Andromedae (Alpheratz, Sirrah) is the brightest star in this constellation. It is a binary star with an overall apparent visual magnitude of 2.1 and a luminosity of 96 suns. It is 97 light-years from Earth. It represents Andromeda’s head in Western mythology, however, the star’s traditional Arabic names- Alpheratz and Sirrah, from the phrase ‘surrat al-faras,’ sometimes translated as ‘navel of the steed’- are a reference to the fact that α Andromedae 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 as ‘Delta Pegasi (δ Peg),’ although this name is no longer formally used.

β And (Mirach) is a red-hued giant star located in an asterism known as the ‘girdle.’ It is 198 light-years away, has a magnitude of 2.06, and a luminosity of 115 suns. 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;

Mirach’s Ghost

As far as ghosts go, Mirach’s Ghost isn’t really that scary. In fact, Mirach’s Ghost is just a faint, fuzzy galaxy, well known to astronomers, that happens to be seen nearly along the line-of-sight to Mirach, a bright star. Centered in this star field, Mirach is also called Beta Andromedae. About 200 light-years distant, Mirach is a red giant star, cooler than the Sun but much larger and so intrinsically much brighter than our parent star. In most telescopic views, glare and diffraction spikes tend to hide things that lie near Mirach and make the faint, fuzzy galaxy look like a ghostly internal reflection of the almost overwhelming starlight. Still, appearing in this sharp image just above and to the right, Mirach’s Ghost is cataloged as galaxy NGC 404 and is estimated to be some 10 million light-years away.

[http://apod.nasa.gov/apod/ap081029.html]

γ And (Almach) is an orange-hued bright giant star 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 5.0, separated by 9.7 arcseconds. The secondary star 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 ‘Anaq al-Ard,’ which means ‘the earth-kid,’ an obtuse reference to an animal that aids a lion in finding prey.

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 four confirmed planets, 0.96 times, 14.57 times, 10.19 times and 1.06 the mass of Jupiter:

This is an artist’s illustration of the Upsilon Andromedae A planetary system, where three Jupiter-type planets orbit the yellow-white star Upsilon Andromedae A.

This is an artist’s illustration that compares the solar system with the Upsilon Andromedae system.

Out of Whack Planetary System Offers Clues to a Disturbed Past:

Astronomers are reporting today the discovery of a planetary system way out of tilt, where the orbits of two planets are at a steep angle to each other. This surprising finding will impact theories of how multi-planet systems evolve, and it shows that some violent events can happen to disrupt planets’ orbits after a planetary system forms, say researchers. For just over a decade, astronomers have known that three Jupiter-type planets orbit the yellow-white star Upsilon Andromedae. Similar to our Sun in its properties, Upsilon Andromedae lies about 44 light-years away. It’s a little younger, more massive, and brighter than the Sun.

Combining fundamentally different, yet complementary, types of data from Hubble and ground-based telescopes, Barbara McArthur’s team of the University of Texas has determined the exact masses of two of the three known planets, Upsilon Andromedae c and d. Much more startling, though, is their finding that not all planets orbit this star in the same plane. The orbits of planets c and d are inclined by 30 degrees with respect to each other. This research marks the first time that the ‘mutual inclination’ of two planets orbiting another star has been measured. And, the team has uncovered hints that a fourth planet, e, orbits the star much farther out.

Until now the conventional wisdom has been that a big cloud of gas collapses down to form a star, and planets are a natural byproduct of leftover material that forms a disk. In our solar system, there’s a fossil of that creation event because all of the eight major planets orbit in nearly the same plane. The outermost dwarf planets like Pluto are in inclined orbits, but these have been modified by Neptune’s gravity and are not embedded deep inside the Sun's gravitational field.

Several different gravitational scenarios could be responsible for the surprisingly inclined orbits in Upsilon Andromedae. Possibilities include interactions occurring from the inward migration of planets, the ejection of other planets from the system through planet-planet scattering, or disruption from the parent star’s binary companion star, Upsilon Andromedae B.

The 14 years of radial velocity information compiled by the team uncovered hints that a fourth, long-period planet may orbit beyond the three now known. There are only hints about that planet because it’s so far out that the signal it creates does not yet reveal the curvature of an orbit. Another missing piece of the puzzle is the inclination of the innermost planet, b, which would require precision astrometry 1,000 times greater than Hubble’s, a goal attainable by a space mission optimized for interferometry.

The team’s Hubble data also confirmed Upsilon Andromedae’s status as a binary star. The companion star is a red dwarf less massive and much dimmer than the Sun. Its orbit could be very eccentric. Maybe it comes in very close every once in a while. It may take 10,000 years. Such a close pass by the secondary star could gravitationally perturb the orbits of the planets.

[http://www.nasa.gov/mission_pages/hubble/science/outofwack.html]

Ross 248

Ross 248 is a nearby red dwarf that is also a flare star (a variable star that displays sudden and unpredictable changes in light output). Ross 248 lies just over 10 light-years away in the constellation Andromeda. Ross 248 was discovered in 1925 by Frank Elmore Ross. Its nearest neighbor is the Gl 15 star system (GX and GQ Andromedae), at a distance of only 1.54 light-years (0.47 pc).

[http://www.daviddarling.info/encyclopedia/R/Ross_248.html]

[http://astroguyz.com/2009/12/14/astro-challenge-groombridge-34-a-nearby-red-dwarf-pair/]

On August 25, 2014, a team of astronomers discovered a super-Earth around Groombridge 34 A in a tight inner orbit. Planetary candidate ‘b’ has around 5.35 ± 0.75 Earth-masses and an orbital period that is a little longer than 11.4 days, which appears to be relatively circular.

Groombridge 34 is located about 11.6 light-years from our Sun, Sol, in the constellation Andromeda, the Chained Maiden- northwest of the Andromeda galaxy (M 31) and two of its satellite galaxies (M32 and M110). This binary star system was listed by Stephen Groombridge (1755-1834. Both visual members of the system are flare stars that have been given the variable star designations GX and GQ Andromedae.

Due to Groombridge 34 AB’s proximity to Sol, the system has been an object of intense interest among astronomers. It was selected as a ‘Tier 1’ target star for NASA’s optical Space Interferometry Mission (SIM) to detect a planet as small as three Earth-masses within two AUs of its host star. Astronomers are also hoping to use the ESA's Darwin group of infrared interferometers to analyze the atmospheres of any rocky planet found in the ‘habitable zone’ (HZ) around Groombridge 34 A for evidence of Earth-type life (Lisa Kaltenegger, 2005).

The precise orbital elements of Groombridge 34 A and B may be uncertain. Based on photographs taken between 1937 and 1970, star A and B are separated by an ‘average’ distance of 147 times the Earth-Sun distance (AU) (of a semi-major axis) in a circular orbit of about 2,600 years.

[http://www.solstation.com/stars/groomb34.htm]

Andromeda Island Universe

The most distant object easily visible to the unaided eye is M31, the great Andromeda Galaxy some two and a half million light-years away. But without a telescope, even this immense spiral galaxy- spanning over 200,000 light years- appears as a faint, nebulous cloud in the constellation Andromeda. In contrast, a bright yellow nucleus, dark winding dust lanes, gorgeous blue spiral arms and star clusters are recorded in this stunning telescopic digital mosaic. While even casual skygazers are now inspired by the knowledge that there are many distant galaxies like M31, astronomers seriously debated this fundamental concept less than 90 years ago. Were these ‘spiral nebulae’ simply outlying components of our own Milky Way Galaxy or were they instead ‘island universes’- distant systems of stars comparable to the Milky Way itself? This question was central to the famous Shapley-Curtis debate of 1920, which was later resolved by observations of M31 in favor of Andromeda, island universe.

[http://apod.nasa.gov/apod/ap080124.html]

Location of M31 in the Andromeda constellation

Andromeda’s borders contain many visible distant galaxies. The most famous deep-sky object in Andromeda is the spiral galaxy cataloged as Messier 31 (M31) or NGC 224 but known colloquially as the Andromeda Galaxy for the constellation. M31 is one of the most distant objects visible to the naked eye; it is seen under a dark, transparent sky as a hazy patch in the north of the constellation. M31 is the largest neighboring galaxy to the Milky Way and the largest member of the Local Group of galaxies. In absolute terms, M31 is approximately twice the size of the Milky Way. It is an enormous- 192.4 by 62.2 arcminutes in apparent size- barred spiral galaxy similar in form to the Milky Way and at an approximate magnitude of 3.5, is one of the brightest deep-sky objects in the northern sky. Despite being visible to the naked eye, the ‘little cloud’ near Andromeda’s figure was not recorded until AD 964, when the Arab astronomer al-Sufi wrote his Book of Fixed Stars. M31 was first observed telescopically shortly after its invention, by Simon Marius in 1612.

The Andromeda Galaxy’s two main companions, M32 and M110 (also known as NGC 221 and NGC 205, respectively) are faint elliptical galaxies that lie near it. M32, visible with a far smaller size of 8.7 by 6.4 arcminutes, compared to M110, appears superimposed on the larger galaxy in a telescopic view as a hazy smudge, M110 also appears slightly larger and distinct from the larger galaxy; M32 was discovered in 1749 by French astronomer Guillaume Le Gentil and has since been found to lie closer to Earth than the Andromeda Galaxy itself. It is viewable in binoculars from a dark site owing to its high surface brightness of 10.1 and overall magnitude of 9.0. M110 is classified as either a dwarf spheroidal galaxy or simply a generic elliptical galaxy. It is far fainter than M31 and M32, with a surface brightness of 13.2, magnitude of 8.9, and size of 21.9 by 10.9 arcminutes.

The Andromeda Galaxy has a total of 15 satellite galaxies, including M32 and M110. Nine of these lie in a plane, which has caused astronomers to infer that they have a common origin. These satellite galaxies, like the satellites of the Milky Way, tend to be older, gas-poor dwarf elliptical and dwarf spheroidal galaxies. M31 is often referred to as a twin sister to the Milky Way, but it has only half the mass of the Milky Way despite being twice its diameter. The futures of the Andromeda and Milky Way galaxies may be interlinked: in about five billion years, the two could potentially begin an Andromeda–Milky Way collision that would spark extensive new star formation.

Along with the Andromeda Galaxy and its companions, the constellation also features NGC 891 (Caldwell 23), a smaller galaxy just east of Almach:

NGC 891 Edge-on

This sharp cosmic portrait features NGC 891. The spiral galaxy spans about 100 thousand light-years and is seen almost exactly edge-on from our perspective. In fact, about 30 million light-years distant in the constellation Andromeda, NGC 891 looks a lot like our Milky Way. At first glance, it has a flat, thin, galactic disk and a central bulge cut along the middle by regions of dark obscuring dust. The combined image data also reveal the galaxy’s young blue star clusters and telltale pinkish star forming regions. And remarkably apparent in NGC 891’s edge-on presentation are filaments of dust that extend hundreds of light-years above and below the center line. The dust has likely been blown out of the disk by supernova explosions or intense star formation activity. Faint neighboring galaxies can also be seen near this galaxy’s disk.

[http://apod.nasa.gov/apod/ap131011.html]

NGC 891 is a barred spiral galaxy seen edge-on, with a dark dust lane visible down the middle. NGC 891 is incredibly faint and small despite its magnitude of 9.9, as its surface brightness of 14.6 indicates; it is 13.5 by 2.8 arcminutes in size. NGC 891 was discovered by the brother-and-sister team of William and Caroline Herschel in August 1783.

Andromeda is also home to the open cluster NGC 752 (Caldwell 28) at an overall magnitude of 5.7. It is a loosely scattered cluster in the Milky Way that measures 49 arcminutes across and features approximately twelve bright stars, although more than 60 stars of approximately 9th magnitude become visible at low magnifications in a telescope. It is considered to be one of the more inconspicuous open clusters. The other open cluster in Andromeda is NGC 7686, which has a similar magnitude of 5.6 and is also a part of the Milky Way. It contains approximately 20 stars in a diameter of 15 arcminutes, making it a tighter cluster than NGC 752.

NGC 7662 (Blue Snowball) in Andromeda

[http://www.capella-observatory.com/ImageHTMLs/PNs/NGC7662.htm]

There is one prominent planetary nebula in Andromeda: NGC 7662 (Caldwell 22). Lying approximately three degrees southwest of Iota Andromedae at a distance of about 4,000 light-years from Earth, the ‘Blue Snowball Nebula’ is a popular target for amateur astronomers. It earned its popular name because it appears as a faint, round, blue-green object in a telescope, with an overall magnitude of 9.2. Upon further magnification, it is visible as a slightly elliptical annular disk that gets darker towards the center, with a magnitude 13.2 central star. The nebula has an overall magnitude of 9.2 and is 20 by 130 arcseconds in size.

Andromeda is also the location of the radiant for the Andromedids, a weak meteor shower that occurs in November.

[https://en.wikipedia.org/wiki/Andromeda_%28constellation%29]
[https://en.wikipedia.org/wiki/Andromeda_Galaxy]
[https://en.wikipedia.org/wiki/Andromeda_%28mythology%29]

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