ANDROMEDA, LADY OF FALL
by Brian Mason
One of the most prominent constellations that can be seen in
the autumn season of the Northern Hemisphere is the chained lady of
the sky, Andromeda. In Greek mythology, Andromeda was the daughter
of Cepheus and Cassiopeia, the King and Queen of Ethiopia.
Andromeda was punished due to the boasting of her mother,
Cassiopeia. In some traditions, Cassiopeia was boasting of her own
beauty, while in others she spoke of the beauty of her daughter,
Andromeda. She was compared in beauty to the Nereids, the water
nymphs, who complained to their father, Poseidon. Poseidon sent the
sea creature Cetus to destroy Ethiopia for this insult. The only
way King Cepheus could avoid this horror was to sacrifice his
daughter to Cetus. Cepheus had Andromeda chained to a rock by the
sea to await her fate. The fates had other intentions, though: The
hero Perseus came upon the scene and, after warning Andromeda to
keep her eyes tightly shut, exposed Cetus to the severed head of
Medusa. This gruesome creature's gaze, even in death, would turn
any living thing it met eyes with into stone. Cetus saw Medusa's
head and was transformed into solid rock. Perseus then freed
Andromeda from her bonds and the two were later married.
While the Greek myth is certainly ancient, the story itself
probably originated even earlier in the region of Mesopotamia (now
modern Iraq) in the Babylonian "Epic of Creation". Elements of the
Greek myth tie in with the Babylonian story of the hero Bel Marduk
and the evil dragon Tiamat.
The Western constellation of Andromeda also shares its stars
with the more complex Chinese constellations Koui-siou (the House of
the Sandal), Kiun-nan-mun (the Southern Camp Gate), and
T'ien-Ta-Tsiang- Kiun (the Great Celestial General). All of these
are part of Pe-Hou, the White Tiger of Autumn. Koui-siou steps
across the center of Andromeda, then across the galaxy Andromeda
(Messier 31, or M31), and finally the star Mirach. The appearance
of this asterism indicated both the time of the harvest and the need
to make footwear. Kiun-nan-mun is near the star Adhil at the right
foot of Andromeda. Kiun-nan-mun, along with many other asterisms of
this part of the White Tiger, is associated with the end of summer
festivals. T'ien-Ta-Tsiang-Kiun is near the star Almech at the left
foot of Andromeda. Gamma Andromeda represented the Great Celestial
General, while surrounding stars represented his officers.
The Marshall Islanders saw a porpoise design in the
constellations Cassiopeia, Andromeda, Triangulum, and Aries. The
tail of the porpoise is the "W" shape of Cassiopeia, with Aries at
the head. Andromeda made up the mid-body and dorsal fin of this
ocean mammal.
Visually from Earth, Andromeda is found between the Milky Way
band of stars and the ecliptic between twenty-three and three hours
right ascension, and between twenty and fifty-five degrees north
declination. The constellation starts at Alpheratz, or Alpha
Andromedae, the north- east star of the Great Square of the mythic
winged horse, Pegasus (which is at the head of Andromeda), and
continues in a generally northeasterly direction. Delta and Pi
Andromedae mark the breasts of Andromeda, Mu Andromedae and Beta
Andromedae (also known as Mirach) mark her waist, while 51
Andromedae and Gamma Andromedae (also known as Almech) mark the feet
of the chained maiden. Lambda Andromedae marks her right chained
hand, while the princess' other hand is vaguely indicated in the
opposite direction. Cassiopeia and Lacerta are to the right of
Andromeda, while the constellations Triangulum and Pisces are to her
left. Pegasus and Perseus are found above and below Andromeda,
respectively.
Alpheratz, or Alpha Andromedae, is a B9 spectral class
spectroscopic binary star system with a period of 97 days. It is
a white star of magnitude 2.1 located roughly one hundred light
years from Earth. Alpheratz means "the horse's navel", attesting to
its former attachment to the constellation of Pegasus, where it was
once known as Delta Pegasi. Another bright star of the same
magnitude is Mirach, or Beta Andromedae. It is a M0 class star
found 170 light years from Sol. Its name means "girdle of the
waist-cloth", which approximates its position in the constellation.
The third magnitude 2.1 star in Andromeda is Almech, or Gamma
Andromedae. It is probably the most interesting of the group. A
trinary star system with components of magnitude 2.1, 5.5, and 6.3,
it consists of orange (K3), emerald (B9), and blue (A0) members,
first recognized as being multiple by Frederich G. W. von Struve
(1793-1864) in 1830. The separation of the closer pair in the
system is from one to ten seconds of arc. Their orbit has a period
of 61 years. Almech is the name of a small predatory animal in
Arabia.
One of the most significant and stunning object in Andromeda
is the galaxy Andromeda (Messier 31, or M31). This spiral star
structure is a relatively bright celestial object at magnitude 4.8.
The galaxy is found at zero hours, 42 minutes right ascension and 41
degrees north declination. Andromeda is one of the few Messier
objects which can be viewed clearly with binoculars, despite being
over 2.2 million light years from our Milky Way galaxy. At this
distance, Sol would have an apparent magnitude of just 29.1. It
should be noted, though, that Andromeda is a next-door neighbor to
the Milky Way compared to most other galaxies in the Universe. When
the light now seen from Andromeda left on its 730 kiloparsec
intergalactic journey, one of humanity's most ancient ancestors,
Homo Habilis, were roaming the grassy plains of East Africa.
The Andromeda galaxy was first mentioned by the Persian
astronomer al-Sufi (903-986) in the Tenth Century and was referred
to as the "little cloud". Andromeda is a spiral galaxy which is
seen about fifteen degrees from edge on and was initially believed
by earlier astronomers to be a cloud of gas or a forming solar
system. The true distance of Andromeda was determined in 1923 with
the use of Cepheid variable stars. This galaxy contains over three
hundred billion suns and the absolute magnitude of the great spiral,
almost twice the size of our own Milky Way galaxy, would be -20.3!
Sol's apparent magnitude in Earth's sky is -27 for comparison. It
is 160 minutes by 40 minutes in diameter, with over one hundred
novae having been discovered there since the invention of the
astronomical telescope. Andromeda is also a strong celestial radio
source at 158.5 megahertz.
Twenty-four minutes south of Messier 31 is the galaxy Messier
32, an elliptical companion galaxy. It is faint (magnitude 8.7) and
small, only 3.6 by 3.1 minutes in size. M32 was discovered in 1749
by Le Gen- tilin. Another even smaller companion to M31 is Messier
110, thirty- five minutes to the northwest. M110 was discovered in
1773 by Charles Messier (1730-1817) and its stellar magnitude is
only 9.4.
There are three annual meteor "showers" associated with
Andromeda, as they appear to emanate from the constellation. Those
occurring on August 31 and October 3 are relatively minor, but the
Andromedids of November 14 can be quite impressive. The radiant of
these is near Gamma Andromedae, and they are best seen in very dark
skies at a usual rate of five to fifteen meteors per hour. This
display is thought to be the remains of the comet Biela, which
failed to reappear in 1872. In 1885 the Andromedids produced from
five thousand to seventy-five thousand meteors per hour!
The chained princess of mythology is one of the larger
constellations in the Northern sky and possesses one of the most
spectacular objects in all of observational astronomy. The history
of Andromeda and her many surrounding constellations form a
fascinating story, well suited for late night observing sessions
under clear and dry autumn skies.
References and Further Reading -
Allen, Richard H., STAR NAMES: THEIR LORE AND MEANING, Dover
Books, New York, 1963 (1899)
Bishop, Roy L., OBSERVER'S HANDBOOK, The Royal Astronomical
Society of Canada (RASC), 1988
Burnham Jr., Robert, BURNHAM'S CELESTIAL HANDBOOK (three vol.),
Dover Books, Mineola, New York, 1978
Menzel, Donald H., and Jay M. Pasachoff, FIELD GUIDE TO THE
STARS AND PLANETS, Houghton Mifflin Company, Boston, 1983
Moore, Patrick, EXPLORING THE NIGHT SKY WITH BINOCULARS,
Cambridge University Press, 1986
Murdin, Paul, CATALOGUE OF THE UNIVERSE, Crown Publishers, 1979
Staal, Julius D. W., THE NEW PATTERNS IN THE SKY, McDonald and
Woodward, Blacksburg, 1988
Staal, Julius D. W., STARS OF JADE, Writ Press, 1984
About the Author -
Brian Mason is currently pursuing a Ph.D. in astronomy with
CHARA while teaching physics at Avondale High School in Atlanta,
Georgia. Brian's interests include binary star astrometry and
photometry, as well as speckle interferometry. He is also active in
astronomical computing.
Brian is the author of "Pegasus: Winged Horse of Autumn" in
the September 1990 issue of the EJASA.