Triangulum
is a tiny
group of stars surrounded by the constellations Perseus to the
north, Andromeda to the north and west, and by the Zodiac constellations
Aries and Pisces to the south. Although it is a small constellation
with only faint stars, Triangulum was known to the ancient star-gazers
and was originally called Deltoton, in reference to the shape
of the Greek letter Delta. Egyptian astronomers also thought of
these stars as a delta, but in the sense of the delta of the river
Nile; and so to them it was named Nili Domus, home of the Nile.
Sicilia is the name given this triangle of stars by Roman philosophers,
who thought it resembled the triangle-shaped island of Sicily.
The Roman goddess Ceres, sister of Jupiter, became the guardian
divinity of Sicily as well as the goddess of agriculture and the
harvest. She implored Jupiter to replicate her island in the sky.
In later times, Sicily became the site for the renowned Palermo
Observatory, founded by Pope Pius VII. Completing the cycle, it
was here on the first day of the nineteenth century—January
1, 1801—that Giuseppe Piazzi observed a "star"
that was not in his catalog. Observing again the following night,
Piazzi found the object to have shifted by several minutes of
arc. He named this planetoid Ceres Ferdinandea, after his patron
goddess and his king. The second part of this name was abandoned
in favor of the tradition of naming the planets for mythological
figures. When first seen, Ceres was among the stars of Taurus,
by coincidence not far from the constellation of Triangulum.
Chinese astronomers include this star pattern together with some
stars of Aries and Andromeda to form their asterism Heaven's Great
General, Tsien Ta Tseang.
Of the stars of Triangulum, only one has a name. That is Caput
Trianguli, head of the triangle.
The Pinwheel Galaxy in Triangulum, M33, is
the principal deep-sky object in the constellation. Also referred
to as NGC 672, this is a very large (62' × 39') spiral galaxy
seen nearly face-on, yet it is not very bright. A member of the
Local Group of galaxies, it is only slightly more distant than
M32, the beautiful Andromeda Galaxy. To locate it, find M31, then
look opposite Mirach, Beta-Andromedae, about an equal distance.
Although it rates a magnitude of 5.5, this light is spread out
over so large an area that only under the darkest skies can it
be seen without binoculars. With a telescope, one needs a wide-field
eyepiece, for the galaxy's fuzzy glow spreads wider than the apparent
diameter of the Moon. In actual size, the galaxy is about half
the diameter of the Milky Way; about one third the size of Andromeda's
M31. It reveals areas of current star formation, with its spiral
arms dominated by young, hot blue stars, and with the presence
of dust and gas. No supernovae have been observed, likely because
none of the stars has evolved to an eventual collapse. If there
should be one, it would probably outshine the entire galaxy at
about sixth magnitude. Supernovae, stars that explode with exceptional
violence, are seen more frequently in other galaxies than our
own, because there are millions of galaxies, each with billions
of stars. Within M33 is a huge cloud of gas, larger than the nebula
in Orion. This is NGC 604, a fuzzball with a spectrum similar
to that of the Lagoon Nebula in Sagittarius.
Another constellation shares the triangle name but not the heritage.
This is Triangulum Australe in the sky of the Southern Hemisphere.
The Southern Triangle is one of the twelve star groups that were
formed into new constellations by Johann Bayer in his 1603 publication,
Uranometria. Bayer had obtained a description of the sky from
the Dutch navigator, Pieter Keyser (Petrus Theodori), who died
in 1596. This enabled him to fill in parts of the southern sphere
unknown to the ancient astronomers. The other constellations of
Bayer were Apis, the Bee (now Musca, the Fly), Avis Indica, the
Bird of Paradise (now Apus), Chamaeleon, the Chameleon, Dorado,
the Swordfish, Grus, the Crane, Hydrus, the Water Snake—not
to be confused with Hydra, the Water Serpent—Indus, the American
Indian, Phoenix, Piscis Volans, the Flying Fish, (now simply Volans),
and Tucana, the Toucan. None of these constellations can be observed
from our Northern California latitudes.