Situated in the northern sky, Andromeda constellation lies between Cassiopeia’s W asterism and the Great Square of Pegasus. Among the 48 Greek constellations, it was first recorded in Claudius Ptolemy’s Almagest during the 2nd century CE.
Named after the legendary princess Andromeda, daughter of Queen Cassiopeia and wife of Greek hero Perseus, this celestial region is also referred to as the Chained Maiden, Persea (wife of Perseus), or Cepheis (daughter of Cepheus). Noteworthy entities within Andromeda include the renowned Andromeda Galaxy (Messier 31) along with the dwarf elliptical galaxies Messier 32 (Le Gentil) and Messier 110. Alpheratz, Mirach, and Almach, the brightest stars within the constellation, form a linkage between the Great Square of Pegasus and Perseus.
Key Facts, Location, and Map
Covering an area of 722 square degrees, Andromeda ranks as the 19th largest constellation in the sky. Positioned in the first quadrant of the northern hemisphere (NQ1), this constellation is observable at latitudes ranging from +90° to -40°. Andromeda is bordered by Cassiopeia, Lacerta, Pegasus, Perseus, Pisces, and Triangulum.
Andromeda, pronounced /ænˈdrɒmɪdə/, is commonly known in English as Andromeda or the Chained Maiden. The genitive form used for star designations is Andromedae (pronounced /ænˈdrɒmɪdiː/). The International Astronomical Union (IAU) has designated the three-letter abbreviation for Andromeda as And since 1922.
Alpha Andromedae, also called Alpheratz, shines as the brightest star in the constellation. The nearest star, Ross 248 (spectral class M6V or HH Andromedae), is a mere 10.30 light years away from Earth. Andromeda boasts three stars brighter than magnitude 3.00 and three stars located within 10 parsecs (32.6 light years) of our planet.
The Andromeda constellation consists of nine designated stars validated by the International Astronomical Union (IAU): Adhil (Xi Andromedae), Almach (Gamma Andromedae A), Alpheratz (Alpha Andromedae Aa), Buna (HD 16175), Mirach (Beta Andromedae), Nembus (51 Andromedae), Sterrennacht (HAT-P-6), Titawin (Upsilon Andromedae A), and Veritate (14 Andromedae A).
Andromeda hosts several stars with confirmed exoplanets. Titawin, Upsilon Andromedae (spectral class F8V), contains four planets in its orbit. The triple star Kappa Andromedae (B9IVn) harbors one confirmed exoplanet, approximately 13 times the mass of Jupiter, initially detected in November 2012. The suspected variable star 14 Andromedae, also known as Veritate (K0III), possesses a known extrasolar planet, discovered in 2008.
HD 5608 (K0IV) presents a transiting planet, while HD 8673 (F7 V) houses a substellar companion identified in 2005, possibly a brown dwarf or a planet. V428 Andromedae (HD 3346, spectral class K5III) reveals two suspected exoplanets, discovered in 1996. Additionally, other stars within Andromeda with confirmed planets include HD 222155 (G2V), HD 16175 (F8 IV), HD 1605 (K1IV, two exoplanets), HD 13931 (G0), HD 5583 (K0), HD 15082 (kA5 hA8 mF4), HAT-P-6 (F), HAT-P-16 (F8), HAT-P-32 (F/G), WASP-1 (F7V), Kepler-63, HAT-P-19 (K), HAT-P-28 (G3), and HAT-P-53.
Andromeda is part of the Perseus constellation family, alongside Auriga, Cassiopeia, Cepheus, Cetus, Lacerta, Pegasus, Perseus, and Triangulum. It contains three Messier objects – Messier 31 (Andromeda Galaxy), Messier 32, and Messier 110.
The constellation is linked to the Andromedids meteor shower (also known as the Bielids), which was first observed on December 6, 1741, in Russia. Although the meteor shower has dimmed since its discovery, slight activity is still visible in mid-November. The Andromedids originate from Biela’s Comet (3D/Biela), a periodic comet initially seen in 1772.
Andromeda myth
In Greek mythology, Andromeda, the daughter of King Cepheus of Ethiopia and Queen Cassiopeia, drew the ire of the Nereids (sea nymphs) by asserting her superior beauty to theirs.
The sea god Poseidon, responding to the nymphs’ complaints, dispatched a sea monster named Cetus to inundate and wreak havoc on Cepheus’ lands as retribution for his wife’s arrogance. Upon seeking guidance from the Oracle of Ammon on averting the total devastation of his kingdom, the king was informed that the sole method to placate the gods and nymphs was to offer his daughter as a sacrifice to Cetus. Consequently, Andromeda was bound to a rock, awaiting the monster’s arrival, until the intervention of the hero Perseus, who rescued her. The two later wed and bore six offspring, including Gorgophonte, who sired Tyndareus, the renowned Spartan monarch, and Perses, an ancestor of the Persian lineage.
In honor of Princess Andromeda, the goddess Athena immortalized her by situating her likeness among the stars alongside the constellations representing her spouse Perseus and mother Cassiopeia.
Main Stars in Andromeda
Alpheratz – α Andromedae (Alpha Andromedae)
The most dazzling star in Andromeda is Alpheratz, also known as Alpha Andromedae or Sirrah. Situated 97 light years away from Earth, Alpheratz shines as a binary star with an apparent magnitude of +2.06. This hot blue B8 subgiant star boasts an extraordinary chemical composition, with notably high levels of mercury, manganese, and other elements. Its luminosity surpasses that of the Sun by 200 times, with a mass of around 3.6 solar masses and a scorching surface temperature of approximately 13,800 K.
Alpheratz dances in space with a partner star, which exceeds the Sun’s mass and shines ten times brighter. The pair gracefully orbit each other every 96.7 days. Initially considered part of the Pegasus constellation, Alpheratz earned dual designations as both Alpha Andromedae and Delta Pegasi. Its names, Alpheratz and Sirrah, stem from the Arabic term al surrat al-faras, translating to “the navel of the horse,” in reference to Pegasus. Arab astronomers also dubbed it al ras al mar’ah al musalsalah, or “the head of the chained woman.”
Positioned as the northeastern star in the Great Square of Pegasus, Alpheratz serves as the link between the Andromeda constellation and Pegasus, the celestial horse ridden by Perseus in his heroic quest to rescue Andromeda.
Mirach – β Andromedae (Beta Andromedae)
Mirach, also identified as Beta Andromedae, shares a similar apparent magnitude range to Alpheratz, fluctuating between +2.01 to +2.10. This star is categorized as a suspected semi-regular variable.
Mirach, a bright red class M giant star located approximately 200 light years away, is 1,900 times more luminous than the Sun and 3-4 times more massive. It is accompanied by a magnitude 14 hydrogen-fusing star. Mirach is part of an asterism known as the girdle, derived from the Arabic word “mizar,” which refers to the star’s position at Andromeda’s left hip.
Situated just seven arcminutes away is the galaxy NGC 404, also known as the Ghost of Mirach, a dwarf lenticular galaxy situated around 10 million light years from Earth.
Almach – γ Andromedae (Gamma Andromedae)
Almach, also known as Gamma Andromedae, is the third brightest star in the constellation. This multiple star system is named after the Arabic term for “caracal” or “the desert lynx,” al-‘anaq al-‘ard. Almach is roughly 350 light years distant. The primary star, Gamma1 Andromedae, is a golden yellow giant, while its blue companion stars are separated by about 10 arcseconds.
The primary star is a class K bright giant, 2,000 times more luminous than the Sun, and approximately 355 light years distant. The companion, Gamma2 Andromedae, forms a binary star system, composed of fifth and sixth magnitude white dwarf stars.
δ Andromedae (Delta Andromedae)
Delta Andromedae, a double star system with an apparent magnitude of 3.28, is located around 101 light years away from the solar system. The brighter primary star is a K-type giant, while its dimmer companion star could be either a G-type main sequence star or a white dwarf.
ι Andromedae (Iota Andromedae)
Iota Andromedae is a bluish-white B-type main sequence dwarf star with a magnitude of +4.29, located 503 light years away.
υ Andromedae (Upsilon Andromedae)
Upsilon Andromedae is a binary star system in the Andromeda constellation consisting of a yellow-white dwarf (Upsilon Andromedae A) with four presumed Jovian planets and a fainter red dwarf (Upsilon Andromedae B). The system is 44 light years from Earth and ranked 21st for the NASA Terrestrial Planet Finder mission.
Adhil – ξ Andromedae (Xi Andromedae)
- Xi Andromedae, also known as Adhil, is a double star with a spectral class of G9, located approximately 196 light years away with an apparent magnitude of +4.875.
51 Andromedae (Nembus)
Nembus, or 51 Andromedae, is an orange K-type giant star with an apparent magnitude of 3.57, situated 177 light years away in the constellation.
Mu Andromedae (μ Andromedae)
Mu Andromedae is a white A-type dwarf star located around 136 light years from Earth, with an apparent magnitude of +3.86.
Other notable stars:
- Pi Andromedae: Pi Andromedae is a binary star system located approximately 660 light years away. The primary star has a brightness of 4.3 magnitude, while its companion is a 9th magnitude star.
- R Andromedae: R Andromedae is a Mira-type variable star that can be observed about four degrees southwest of the Andromeda Galaxy. Its brightness fluctuates between magnitudes 5.8 and 14.9 over a period of 409 days.
- RX Andromedae: RX Andromedae is a Z Camelopardalis-type variable star. It displays variations in brightness ranging from magnitude 10.3 to 14 within a 14-day cycle.
- 56 Andromedae: 56 Andromedae is a binary star system composed of two components, both with a magnitude of six.
- Groombridge 34: Groombridge 34 is a binary star system containing two red dwarf stars. Situated just 11.7 light years away, it stands out as one of the closest double star systems to the Sun. The two constituent stars are named GX Andromedae (Groombridge 34 A) and GQ Andromedae (Groombridge 34 B).
Deep sky objects in Andromeda
Andromeda Galaxy (Messier 31, M31, NGC 224)
The Andromeda Galaxy, also known as Messier 31 (M31) or NGC 224, is a spiral galaxy located around 2.5 million light years away. Previously mistaken for the Great Andromeda Nebula, it stands as the closest spiral galaxy to the Milky Way and the most distant object visible to the naked eye in the night sky. With an apparent magnitude of 3.4, it is considered one of the brightest Messier objects, housing approximately a trillion stars—surpassing the Milky Way’s 200-400 billion star count.
When observed through a small telescope, only the bright central region of the Andromeda Galaxy is visible; however, using a larger telescope, its width becomes approximately six times that of the full Moon. As a member of the Local Group of galaxies that includes the Milky Way, Triangulum Galaxy (Messier 33), and about 30 smaller galaxies, Andromeda holds the title of the group’s largest galaxy. Its mass is estimated to be similar to that of the Milky Way, and both galaxies are predicted to collide roughly 4.5 billion years from now.
Satellites of Andromeda Galaxy
Andromeda Galaxy is orbited by a minimum of 14 dwarf galaxies, which include M32 and M110. Additional satellite galaxies, dimmer in comparison, remained undiscovered until the 1970s. These satellites comprise dwarf spheroidal galaxies such as NGC 147 and NGC 185, along with the Cassiopeia Dwarf (Andromeda VII) in the Cassiopeia constellation. In the Andromeda constellation, there are Andromeda I, Andromeda II, Andromeda III, Andromeda V, Andromeda VIII, Andromeda IX, and Andromeda X.
The Pegasus constellation hosts Andromeda VI, also known as the Pegasus Dwarf Spheroidal galaxy. Furthermore, located in Pisces constellation is Andromeda XXII, recognized as Pisces VI or Triangulum I. Notably, the Triangulum Galaxy (M33), a renowned spiral galaxy in the Triangulum constellation, is believed to be another satellite of the Andromeda Galaxy.
NGC 206 Star Cloud
NGC 206, a star cloud in the Andromeda Galaxy, stands as the brightest star cloud in M31 visible from Earth. It ranks among the largest star-forming regions within the Local Group of galaxies, boasting a collection of intensely luminous stars. Found in a hydrogen-free area within one of Andromeda’s spiral arms, NGC 206 spans around 400 light years and appears with an apparent size of 4.2 arcminutes.
Andromeda’s Cluster – Mayall II
Mayall II (NGC 224-G1) constitutes a globular cluster encircling the Andromeda Galaxy. This cluster rests roughly 130,000 light years from the core of M31 and is recognized as the brightest globular cluster among the Local Group of galaxies. Exhibiting an apparent magnitude of 13.7, Mayall II holds considerable prominence within the galactic neighborhood.The cluster is twice as massive as Omega Centauri, the largest globular cluster in the Milky Way. It is believed to house an intermediate-mass black hole at its core. Some astronomers suggest that Mayall II is not a genuine globular cluster but rather the remaining nucleus of a dwarf galaxy that was assimilated by the larger M31.
Named after the American astronomer Nicholas Mayall, who, together with O.J. Eggen, discovered it in 1953.
Messier 32, a dwarf elliptical galaxy about 2.65 million light years away, was first observed by French astronomer Guillaume Le Gentil in 1749. It is occasionally referred to by the astronomer’s surname, Le Gentil. The galaxy serves as a satellite to the Andromeda Galaxy and was the first elliptical galaxy to be identified. M32, though small, is quite luminous and easily visible through a small telescope.
Positioned 22 arcminutes south of Andromeda’s central area, M32 appears to stretch across Andromeda’s spiral arms, likely on the side facing us. The galaxy is devoid of any globular clusters. It is speculated that M32 was once much larger but shed its outer stars and globular clusters during a collision with the Andromeda Galaxy. About 6,500 light years in diameter, M32 consists mainly of old stars with no ongoing star formation, featuring a supermassive black hole at its center estimated to weigh between 1.5 and 5 million solar masses. Alongside Messier 110, M32 is the nearest bright elliptical galaxy to our solar system.
Messier 110, also known as NGC 205.Messier 110, a dwarf elliptical galaxy often classified as a dwarf spheroidal galaxy, hosts eight globular clusters in its surrounding halo.
Uncharacteristic of a dwarf elliptical galaxy, M110 displays indications of recent star formation and lacks a supermassive black hole at its center, or evidence thereof.
First observed by Charles Messier in 1773 alongside the Andromeda Galaxy, M110 was not originally listed among his discovered objects. It was later independently discovered by Caroline Herschel and documented by her brother William Herschel in 1785. However, the galaxy was not officially included in the Messier catalog until 1967 by Kenneth Glyn Jones.
NGC 752
NGC 752 (Caldwell 28) is an open cluster with an apparent magnitude of 5.7, situated approximately 1,300 light years away from Earth. Discovered by Caroline Herschel in 1783, the cluster might have been observed earlier by Giovanni Batista Hodierna before 1654. It was cataloged by Caroline Herschel’s brother, William Herschel, in 1786.
Bright, sizable, and easily visible through binoculars, NGC 752 can even be spotted with the unaided eye in exceptionally clear conditions. None of the stars within the cluster shine brighter than 9th magnitude.
NGC 891
NGC 891 presents itself as an edge-on spiral galaxy situated four degrees to the east of Almach (Gamma Andromedae). Visible through 4.5-inch telescopes, this galaxy shines at an apparent magnitude of 10.8, positioned approximately 27.3 million light years away from Earth. Spanning an area of 13’.5 x 2’.5, it resembles the Milky Way as if seen edge-on.
This galaxy was first sighted by William Herschel on October 6, 1784, and is part of the NGC 1023 Group. A supernova, known as SN 1986J, illuminated the galaxy on August 21, 1986, reaching a peak magnitude of 14.
NGC 7686
NGC 7686 stands as an open cluster with an apparent magnitude of 5.6, positioned 900 light years away. Comprising around 80 stars, this cluster is easily observable with binoculars and small telescopes.
Blue Snowball Nebula – NGC 7662
The Blue Snowball Nebula, also known as Snowball Nebula in the New General Catalogue as NGC 7662, presents itself as a planetary nebula with an apparent magnitude of 8.6, visible a degree west of the magnitude 4 star Kappa Andromedae. The nebula’s distance is approximated to range between 2,000 and 6,000 light years, enveloping a central bluish dwarf star with a temperature estimate of 75,000 K. With an estimated radius of 0.8 light years, the Blue Snowball Nebula can be observed in a small refractor telescope, appearing like a star-like object with subtle nebulosity
NGC 68 Cluster
The NGC 68 Cluster, also known as Arp 113, consists of over 40 galaxies with NGC 68 at its heart. Situated approximately 300 million light years away, this cluster was first identified by William Herschel in 1784, who initially recorded the galaxies as a singular entity. Later in the 1880s, Danish-Irish astronomer John Louis Emil Dreyer discerned individual members naming some as NGC 68, NGC 70, and NGC 71.
NGC 67a is an elliptical galaxy of the E5 type. It has a visual magnitude of 14.7 and is situated 287 million light years away. The galaxy occupies an area of 0.4’ by 0.2’, translating to a real size of 35,000 light years.
NGC 69 is a lenticular galaxy (S0) with an apparent magnitude of 14.7. Positioned at a distance of 300 million light years, it spans 80,000 light years, or 0.9’ x 0.8’ in the apparent sky.
NGC 70 is a spiral galaxy expanding 180,000 light years. With a visual magnitude of 13.5, it is around 320 million light years distant. The galaxy covers an area of 1.7’ x 1.4’.
NGC 71 is an elliptical or lenticular galaxy (E5/S0) approximately 130,000 light years across, situated about 310 million light years from the Sun. It is the second-largest galaxy in the group, smaller only than NGC 70. This galaxy has an apparent magnitude of 13.2.
NGC 72 is a spiral galaxy with a bar feature, having an apparent magnitude of 13.5 and lying roughly 320 million light years away. It spans about 120,000 light years, equivalent to an apparent size of 1.3’ x 1.0’.
NGC 72a, another galaxy in the group, is an elliptical (E3) galaxy. It is located at a distance of 308 light years and has a visual magnitude of 14.7. The galaxy has an apparent size of 0.3’ x 0.3’ and a real size of 25,000 light years.
NGC 74 is a spiral galaxy that stretches 65,000 light years. It is positioned 315 million light years away with an apparent magnitude of 15.3. Discovered by the Irish astronomer William Parsons on October 7, 1855.
Arp 65 – NGC 90 and NGC 93
NGC 90 and NGC 93 are a pair of interacting spiral galaxies situated in the Andromeda constellation. They were first identified by R.J. Mitchell in 1854. NGC 90 is located 333.8 million light years away with an apparent magnitude of 13.7 and dimensions of 2.4’ x 0.91’. This galaxy exhibits two elongated spiral arms distorted by starburst activity likely triggered by their interaction. On the other hand, NGC 93, positioned 259.7 million light years from Earth, has a visual magnitude of 14.34 and spans an area of 1.4’ x 0.7’.
Ghost of Mirach – NGC 404
NGC 404 is a solitary dwarf lenticular galaxy residing just outside our Local Group. Discovered by William Herschel in 1784, this galaxy has an apparent magnitude of 11.2 and is approximately 10 million light years away. Its size measures 3.5’ x 3.5’, and it’s famously known as the Ghost of Mirach due to its challenging observation and photography given its proximity of 7 arcminutes to the star Mirach. Andromeda contains various deep sky objects listed in the New General Catalogue.
These objects include open cluster NGC 272, spiral galaxies such as NGC 11, NGC 13, NGC 21, NGC 228, NGC 48, NGC 214, NGC 218, NGC 226, NGC 260, NGC 280, NGC 39, NGC 27, NGC 19, NGC 169, NGC 184, NGC 140, NGC 109, NGC 160, and NGC 112, as well as lenticular galaxies like NGC 81, NGC 149, NGC 20, NGC 76, NGC 69, NGC 229, NGC 243, NGC 304, NGC 43, NGC 80, NGC 393, NGC 389, NGC 94, NGC 258, NGC 96, NGC 108, NGC 86, and NGC 252.
Additionally, there are elliptical galaxies: NGC 5, NGC 49, NGC 233, NGC 1000, NGC 79, NGC 97, NGC 83, and NGC 183.
