Constellations: Frequently Asked Questions
Throughout the centuries, people have looked to the
stars to help them navigate across open oceans or featureless
deserts, know when to plant and harvest, and preserve
their myths and folklore. Ancient peoples used the appearance
or disappearance of certain stars over the course of
each year to mark the changing seasons. To make it easier
to "read" this celestial calendar, they grouped the brighter
stars into readily recognizable shapes, the constellations.
Astronomers officially recognize 88 constellations covering
the entire sky in the northern and southern hemispheres.
Currently, 14 men and women, 9 birds, two insects,
19 land animals, 10 water creatures, two centaurs, one head
of hair, a serpent, a dragon, a flying horse, a river and 29
inanimate objects are represented in the night sky (the total
comes to more than 88 because some constellations include
more than one creature.) It is important to realize that the
great majority of star patterns bear little, if any, resemblance
to the figures they are supposed to represent and whose
name they bear. The ancient constellation-makers probably
meant for them to be symbolic, not literal, representations of
their favorite animals or fabled heroes, a kind of celestial
"Hall of Fame."
Our modern constellation system comes to us from the
ancient Greeks. The oldest description of the constellations
as we know them comes from a poem, called Phaenomena,
written about 270 B.C. by the Greek poet Aratus. However,
it is clear from the poem that the constellations mentioned
originated long before Aratus' time. No one is sure exactly
where, when, or by whom they were invented. And yet a little
detective work reveals a plausible origin.
The first clue is that Aratus' constellations did not include
any near the south celestial pole (the point on the celestial
sphere directly above the Earth's south pole) because that
area of the sky was always below the horizon of the ancient
constellation-makers. From the size of this uncharted area
of the sky, we can determine that the people responsible for
the original constellations lived near a latitude of 36° north --
south of Greece, north of Egypt, but similar to the latitude of
the ancient Babylonians and Sumerians.
In addition, the constellation-free zone is not centered
exactly on the south celestial pole. Because of a "wobble" of
the Earth's axis of rotation, the position of the celestial poles
changes slowly with time, a phenomenon known as precession.
The uncharted area is centered on the place in the sky
where the south celestial pole would have been around the
year 2000 B.C. This date matches the time of the
Babylonians and Sumerians.
Thus it seems likely the Greek constellations originated
with the Sumerians and Babylonians. From there, knowledge
of the constellations somehow made its way to Egypt
(perhaps through the Minoans on Crete who had contact with
the Babylonians and settled in Egypt after an explosive
volcanic eruption destroyed their civilization), where early
Greek scholars first heard about the constellations and wrote
In 150 A.D., the Greek scientist Ptolemy published a
book, known by its Arabic name,
The Almagest, which
contained a summary of Greek astronomical knowledge,
including a catalog of 1022 stars, with estimates of their
brightness, arranged into 48 constellations. These 48
formed the basis for our modern constellation system.
Over the years, astronomers have added constellations
to fill in the gaps between Ptolemy's figures and map the
uncharted regions of the sky near the south celestial pole.
Major contributors of new constellations included Dutch
cartographer Gerardus Mercator in 1551 and Pieter Keyser
and Frederick de Hautmann, navigators aboard some of the
first trading expeditions to the East Indies in the early 1600s,
who mapped the southern sky. Polish astronomer Johannes
Hevelius in 1690 and French astronomer Nicolas Louis de
Lacaille in the 1750s filled in the remaining gaps in the
northern and southern skies.
Over the centuries, some astronomers have attempted
to name constellations after themselves or to flatter a patron
or king. This reached a peak during the heyday of celestial
mapping in the seventeenth and eighteenth centuries. Few
of these survived longer than the astronomers who named
them, although they sometimes can be seen in antique star
charts. For example, in 1678, Edmond Halley (of Halley's
Comet fame) invented a constellation called Robur
Carolinum, or Charles' Oak, in honor of King Charles II of
England. This constellation did not last long, especially after
its rejection by the French astronomer Lacaille in his maps of
the southern sky. In 1754, the English naturalist and noted
satirist John Hall invented thirteen constellations based on
rather unappealing animals such as a toad, a leech, a spider,
an earthworm, and a slug. Fortunately, even though they
may have been intended as a joke, they never caught on.
At its first meeting in 1922, the International Astronomical
Union (IAU), astronomy's governing body which is responsible,
among other things, for assigning names to
celestial objects and features on those objects, officially
adopted the list of 88 constellations that we use today.
Definitive boundaries between constellations, which extend
out beyond the star figures, were set in 1930, so that every
star, nebula, or galaxy, no matter how faint, now lies within
the limits of one constellation. For today's astronomer,
constellations refer not so much to the patterns of stars, but
to precisely defined areas of the sky.
The ancient Greek tradition was to name stars by their
position within a constellation. For example, Ptolemy refers
to one star by the description "the reddish one on the
southern eye," a star we now know as Aldebaran in the
constellation of Taurus the Bull. But these descriptions could
get quite involved. Ptolemy refers to another star in the
obsolete constellation of Argo the Boat as "the northernmost
of two stars close together over the little shield in the poop,"
a bit cumbersome if you are trying to learn the names of many
When Al-Sufi, one of the greatest Arabic astronomers,
published his own version of Ptolemy's Almagest in the tenth
century, he introduced many individual star names. For
centuries, bedouin Arabs had given names to bright stars --
for example Aldebaran and Betelgeuse -- since they
regarded single stars as representing people and animals.
Many of the original meanings of the names had been
forgotten even in Al-Sufi's time, but some were direct translations
of Ptolemy's descriptions. For example, the star
name Fomalhaut (in the constellation of Pisces) comes from
the Arabic for "mouth of the southern fish," which is how
Ptolemy described it in the Almagest.
After the tenth century, the works of Ptolemy and others
were re-introduced into Europe by the Islamic Arabs, and the
Greek books were translated from Arabic into Latin, the
scientific language of the day. Thus we know Ptolemy's work
from its Arabic translation, The Almagest, not by its original
Greek title. And it explains why we have a system of Greek
constellations with Latin names containing stars with Arabic
Nearly every culture on Earth has seen patterns in the
stars. But, not surprisingly, very few have seen the same
patterns. Take, for example, the Big Dipper, perhaps the
most recognizable star pattern in the sky. The Big Dipper is
not actually a constellation itself, but is part of a larger pattern
known to the Greeks as Ursa Major, the Great Bear. The
seven stars of the Big Dipper have inspired many stories,
perhaps because they are bright and located so near the
north celestial pole, around which the stars rotate during the
course of the night. But not everyone calls it a Dipper. The
British call it a Plough. In Southern France, it is a Saucepan.
The Skidi Pawnee Indians saw a stretcher on which a sick
man was carried. To the ancient Maya, it was a mythological
parrot named Seven Macaw. Hindu sky lore called it the
Seven Rishis, or Wise Men. To the early Egyptians, it was
the thigh and leg of a bull. The ancient Chinese thought of
it as a special chariot for the Emperor of the Heaven or some
other celestial bureaucrat. For the Micmac Indians of
Canada's Maritime Provinces, along with several other
North American Indian tribes, the bowl of the Big Dipper was
a bear, and the stars in the handle represented hunters
tracking the bear. And in the nineteenth century, the Big
Dipper became a symbol of freedom for runaway slaves,
who "followed the Drinking Gourd" to the northern states.
No. With few exceptions, the stars in a constellation
have no connection with one another. They are actually at
very different distances from the sun (see Activity Corner)
Chance alignments of stars have created the
patterns we see in the sky.
Ancient astronomers often spoke of the "fixed stars,"
which maintained permanent positions in the sky. And,
indeed, the stars do seem almost fixed in place; the patterns
they form look much the same today as they did when the
constellations were first named nearly 3000 years ago. But
the stars are all moving relative to the Sun, most with speeds
of many kilometers per second. Because they are so very far
away, it will take thousands of lifetimes to see significant
changes in the star patterns. But, over time, they will
change. Because of the motions of the stars within it, for
example, the handle of the Big Dipper will, in about 50,000
years, appear significantly more bent than it is today (see
figure at left). We will, no doubt, keep the same names for
the constellations, even if the stars change their positions.
Constellations are, after all, products of human imagination,
Given a star chart without constellation figures
marked on it (whether real star charts or made-up star
patterns), students can invent their own constellations,
looking for patterns in the stars that appeal to them.
Students can then be asked to make up stories to go with
their new constellations.
Older students can research the constellation patterns
and stories that other cultures saw in the night sky and
compare them to the more familiar Greek ones. This can
be done by reading books and articles, or by interviewing
family members or friends.
Maps of the stars in the constellations can be useful in
the classroom. Slide sets, such as Star Maps (a sample
of which is on the front page of this newsletter) which
show actual pictures of each constellation in the night sky
and separate line drawings of the constellation figures,
can help students identify the constellations as part of
homework assignments or evening "star parties." This
can be especially helpful for students without easy access
to a planetarium.
Especially for Younger Children:
- Allen, R. Star Names: Their Lore and Meaning. 1899, 1965,
Dover Books reprint.
- Krupp, E. Beyond the Blue Horizon: Myths and Legends of the
Sun, Moon, Stars and Planets. 1991, Harper Collins.
- Proctor, P. Star Myths and Stories. 1972, Exposition Press.
- Ridpath, I. Star Tales. 1988, Universe Books.
- Rey, H. A. Find the Constellations. 1976, Houghton-Mifflin. A
classic guide with simplified diagrams and text.
- Schatz, D. Astronomy Activity Book. 1991, Simon and Schuster.
Wonderful book of astronomy activities for the whole family or
elementary and middle schools.