Andromeda
is one of a number of constellations that derive their names from
the same epic Greek myth. Also from this story come Cepheus, Cassiopeia,
Perseus and Pegasus, all in the same general region of the northern
sky, as well as Cetus to the south. Andromeda is best known because
it is home to the Great Nebula, M31, called the sister galaxy
to our own Milky Way.
Although Andromeda occupies a large expanse of the night sky,
it contains but six stars brighter than magnitude 4. And, ironically,
the brightest of these, magnitude 2.1 Alpheratz, must be shared
with the asterism of the Great Square of Pegasus as the northeast
(upper left) corner. On some star charts it is still designated
as Delta Pegasi.
The well known legend of the chained princess and her rescue by
the hero Perseus is likely a reinterpretation of an even older
story. The myth of a hero who slays a vile monster (Cetus) is
the same as that of Saint George and the Dragon, of Marduk and
Tiamet, of many a fairy tale. Andromeda may originally have been
the dawn, whose beauty is released from the dark of night by the
conquering Sun-hero.
The stories of Andromeda, the daughter of Cepheus and Cassiopeia,
king and queen of Ethiopia, have been told for more than two thousand
years, but the light that strikes your eye from the faint smudge
that is the Great Galaxy has been traveling through space for
more than two million years. If you have good eyes and a clear
fall night without moonlight, M31 is the most distant object that
can be seen without optical aid. Records show that this object
was known to Persian philosophers in the tenth century and it
was shown on fourteenth and fifteenth century Dutch and Spanish
charts. But first mention of this celestial patch of light is
credited to Simon Marius, who observed it with his telescope in
1612, even before the 1619 discovery of the conspicuous nebula
in Orion. This was the time of the introduction of the first telescopes
in Europe, and more and fainter such cloud-like visions were announced
as the known world of astronomy expanded. By Herschel's time the
perceived abundance of stars and the complexity of their distribution
led him to suggest, in 1785, that a nebula might be a "stupendous
sidereal system … consisting of many millions of stars …
." The English astronomer William Huggins offered proof of
this theory in 1864, using spectrographic measurements. Not until
Edwin Hubble, working with the newly completed 100-inch telescope
at Mount Wilson in 1924, were photographic plates obtained that
resolved the stars of the Andromeda Nebula and made certain that
this distant pinwheel of light should be called instead the Andromeda
Galaxy.
The Andromeda spiral NGC 224 (M31) is located 2.3 million light
years from us, and is about fifty percent larger than our own
galaxy. Find it about 13 degrees west of Gamma Andromedae, Almach,
and an equal distance northeast of Alpha Andromedae, Alpheratz.
It has a pair of companion galaxies, NGC 205 (M110) and NGC 221
(M32), as does our own Milky Way Galaxy, the Large and Small Magellanic
Clouds (which may be observed only from the Southern Hemisphere).
An interesting edge-on spiral galaxy in Andromeda
is NGC 891, located 40 million light years away. This CCD image,
showing the prominent equatorial dark lane, was captured by Jim
Scala. It is only of magnitude 12, but this fine object can be
well observed with an 8-inch telescope if the night is dark, clear
and moonless. It is located about three degrees east of Gamma
Andromedae, or Almach, the second-magnitude star at the tip of
the southern tine of the long, narrow V that identifies the constellation.
Almach is one of the finest of all double stars. Its primary star
is a bright orange, with its double appearing as bluish or blue-green,
separated by about 10 arcseconds. The secondary is itself a very
close double star, but it is seen as a single star because the
elongated orbit of its companion is generally not resolvable by
telescopes. South-southwest of Almach is a large open cluster
of stars that can be appreciated through a good pair of binoculars.
This is NGC 752, whose stars are perhaps 1300 light years away.
The star classifications indicate that they are at least one and
a half billion years old. Another star of note is R Andromedae,
a Mira-class variable star whose magnitude ranges from 5.1 to
14.8 over a period of 409 days.
There are a number of other multiple stars, variable stars, and
other objects that lie in the direction of Andromeda, making it
an important constellation in the night skies of autumn.