Constellations

The Major Constellations:

Andromeda | Aquarius | Aries | Cancer | Capricornus | Cassiopeia | Cepheus | Cetus | Corona Borealis | Cygnus | Draco | Eridanus | Gemini | Hercules | Hydra | Leo | Libra | Lyra | Orion | Perseus | Pisces | Sagittarius | Scorpius | Taurus | Ursa Major | Ursa Minor | Virgo

Supporting References:

Introduction

In this section we learn about the constellations, the fundamental divisions of the sky.

Few constellations look like the animal or person they are named after, and you should not be frustrated if you cannot see a princess, bear, or winged horse in the sky. Only in a few cases can the stars be connect­ed to be made to look like a man, a lion, or a swan. Many constellations were named in honor of heroes, beasts, and objects of interest to the people who named them, and not because of any physical resemblance. We do similar things today: the state of Wash­ington looks nothing like the gentleman on the U. S. dollar bill, nor does the bridge in New York City. The exceptions are few, among them Orion, Scorpius, Gemini, and Taurus.

During the Renaissance, when star maps were designed to be beauti­ful, as well as useful, they were filled with elaborate and colorful drawings that often ignored the background stars. Over time, there was more than one way of drawing the ‘connect-the-dot’ stick figures, which we make to identify the constellations. In any case, there are no “official”, or correct ways to connect the stars, and you are free to invent your own designs if you like.

Asterisms

Some common star patterns are not actual constellations. These asterisms (from aster, the Greek word for star) can be part of one constel­lation or parts of two or more constellations. These are a few of the major asterisms:

  • Big Dipper: The seven brightest stars of Ursa Major.
  • Great Square of Pegasus: The three brightest stars of Pegasus and the westernmost bright star of Andromeda.
  • Keystone: Four medium-bright stars in Hercules that form a square
  • Little Dipper: The seven brightest stars in Ursa Minor.
  • Sickle: Stars in Leo in the shape of a harvesting sickle (or a backwards question mark).
  • Summer Triangle: The stars Vega in Lyra, Deneb in Cygnus, and Altair in Aquila.

Constellations have both a formal Latin name (Aquarius, for exam­ple) and a common English equivalent (Water Carrier). This differs from star names, which are mostly Arabic. Some constel­la­tions pre-date the Latin-speaking Romans, but Latin was the lang­uage of scholarship until recent­ly, and the Latin names were standardized long ago. New constel­la­tions invented in modern times (such as Leo Minor) were given Latin names to conform with ancient custom.

At any given moment you can see half the sky – and approximately half the constellations. As the hours pass and the sky rotates over­head, constellations in the west set and are replaced by others that rise in the east. During the course of a long winter night you can see perhaps two-thirds of the sky, and during the course of a year even more. But – unless you live on the equator – some constellations remain permanently hidden from view. The far southern constellations are a mystery to us in the Northern Hemisphere, and their names – Dorado, Tucana, Centaurus – sound romantic.

Just as the constellations that lie far to the south remain out of sight (assuming you live at a mid-northern latitude), the constellations far to the north remain visible all year. They do not change with the seasons, al­though they are more easily visible at one time of year than another. Because they are always available, they seem to have less value and we take them more for granted. The Big Dipper is above North America for much of the year and has little novelty – yet Austra­lians never see it.

The most popular and best-known constellations are the 12 that make up the classical zodiac. This is true even though half of the zodiacal constellations contain few, if any, bright stars and are not conspicuous, and several cannot be seen from urban areas. They are well-known because of their astrological associations, but their fame does not corres­pond to their visibility. It is ironic that everyone has heard of Cancer, although few could find it, while comparatively few people have heard of Auriga, which is a magnificent constellation of bright stars that is filled with star clusters. Just as some people are famous because of where they are (the position they have in our society) rather than who they are, so it is with the constella­tions. A constel­la­tion’s popularity tells you nothing about how interesting it is.

The Big Dipper

The Big Dipper is a good entry point for learning about the positions of certain stars in the night sky. This asterism is circumpolar when viewed from mid-latitudes in the Northern Hemisphere. This means that it never completely sets below the horizon and is always visible in the night sky.

The Big Dipper itself is not a constellation, but is an asterism within the constellation of Ursa Major. Ursa Major is also known as the Great Bear and is the third largest of the 88 constellations. The name originates from the ladle-shaped pattern formed by the seven main stars in the constellation.

This asterism can be found by facing north, as shown in the view in the Main Window. At certain times of the year the Big Dipper will look like a ladle lying upon a table; at other times of the year the ladle will appear to be upside down. The actual shape of the Big Dipper does not change over time, only its apparent orientation.

  • In autumn, the dipper appears to be lying flat.
  • In spring, the dipper is upside down, “spilling” its contents.
  • In summer, it sits upright on its bowl
  • In winter, it sits with its handle downwards.

Big Dipper

What’s in a Name?

The Big Dipper asterism is primarily seen a ladle in North America. Different cultures, however, see different things when they look at the Big Dipper. In England it is known as the Plough, in Germany as the Great Cart and in western Africa as the Drinking Gourd.

Star hopping

The stars of the Big Dipper act as a handy guide to the positions of other stars and constellations, and to other objects that may be too faint to spot with the naked eye. Using well-known stars in the sky to find fainter objects is known as “star hopping”. You can think of this as an astronomical treasure hunt!

The most useful alignment for observers in the northern hemisphere is produced by the two end stars that form the front of the dipper’s bowl. A line projected from these two stars points directly at Polaris, the North Star. The position on the horizon directly below Polaris is almost exactly north; a very useful direction should you become lost (without your GPS!).

16_Navigating%20with%20the%20Big%20Dipper

All the other stars in the sky seem to turn counter-clockwise around Polaris. Polaris itself marks the end of the handle of another pattern or asterism, the Little Dipper.

A second star-hopping line from the Big Dipper follows the curved handle of the Big Dipper to two of the northern hemisphere’s brightest spring stars, Arcturus and Spica. This star-hopping technique becomes surprisingly easy with a bit of practice.

Polaris and latitude

Polaris is a very special star for northern hemisphere dwellers and navigators. It is only about 1 degree away from the North Celestial Pole (NCP), the point directly above the north end of the Earth’s spin axis. This easily enables us to orient ourselves on Earth on a clear night.

The North Celestial Pole (NCP) offers an additional navigational benefit, in addition to defining north. An astrolabe is a device that can determine your latitude by measuring the angle between the horizon and Polaris. Astrolabes were regularly used by early explorers and by mariners on sailing ships.

Astrolabe_(PSF)

The south star?

People living in the Southern Hemisphere are not quite as fortunate as those in the Northern Hemisphere. There is no bright star the equivalent of Polaris to mark the location of the south celestial pole in their sky.

Measuring distances

Measuring the angular distances between stars is easy if you use your hand, held at arm’s length.

With your hand at:

  • the width of your little finger is about one degree, enough to cover the Moon and Sun. These objects are each half a degree across.
  • the width of the first three fingers side-by-side spans about five degrees.
  • a closed fist is about ten degrees.

if you spread out your fingers, the distance from the tip of your first finger to the tip of your little finger is 15 degrees. The distance from your little finger to your thumb covers about 25 degrees of sky.

14_Handy%20Measures

This hand system, with a bit of practice, can be very useful for measuring angles in the sky.

Calibrating with the Big Dipper

Everyone’s hands are slightly different, so you might want to “calibrate” your own hand measurements using the Big Dipper.

13_Dipper%20Distances

Here are the approximate angular distances from Dubhe to several other prominent Big Dipper stars:

Dubhe to Merak

5 degrees

Dubhe to Megrez

10 degrees

Dubhe to Alioth

15 degrees

Dubhe to Mizar

20 degrees

Dubhe to Alkaid

25 degrees

History of the Constellations

Humans have the need, and the skills, to find patterns in nature. Our brains are programmed to invent patterns and to impose order on dis­order. This talent helped our remote ancestors find their way around hunting and scavenging sites, and it helps us find our way around the sky.

We also have a need to feel connected to the cosmos. Being completely inaccessible, the sky is an endless source of mystery and wonder. It takes a soulless person indeed to gaze up at the sky on a dark, starry night and not wonder how we fit into it all. People have been doing just that since the beginning of time.

The origins of most constellations are lost in the mists of antiquity, and some of them are prehistoric. We can only unravel as much as we can of the origins and history of the oldest constellations by using the sparse clues available to us. Others were created in more recent times and their history is doc­u­ment­ed, and the far southern constellations were out­lined and named during the Age of Exploration only several cen­turies ago. As recently as early last century astronomers were pro­posing new ones, but their number was fixed at 88 early this century and the days of creating new constella­tions are over.

The core of our familiar western constellations probably originated in pre­his­toric Sumeria. The Sumerians, who lived in the arid land between the Tigris and Euphrates Rivers in what is now southern Iraq, developed one of the world’s first great civilizations and counted the invention of writ­ing among their achievements. They were a super­stitious folk, and they paid great attention to corres­pondences between events in the sky and events on earth. They saw the seasons as a cyclic battle between the Lion and Bull. In mid-winter 6,000 years ago, Leo the Lion stood high over­head while Taurus the Bull lay “dying” on the western horizon, and the lion was trium­phant. The re­appear­ance of the Bull in the morning sky marked the return of spring and the death of winter, and the Bull’s turn to triumph. They chart­ed the stars to try to fig­ure out what was happening to them and to the world around them, and their ideas of inter­preting omens were elabor­at­ed upon by the Babylonians, who lived in the same area much later. The Babylonians left the first con­stel­lation lists on clay tablets, and they invent­ed the idea of the zodiac around the 6th century BC.

The Oldest Constellation?

The Great Bear (the brightest part of which is the Big Dipper) is probably the oldest constellation, and it dates to prehistoric times. Bears were worshipped in “cave man” days in Europe, before they became extinct (in Europe) at the end of the last Ice Age. Bears are still wor­ship­ped by nomadic people in Siberia.

People named the celestial Great Bear for its behavior. It does not look like a bear, but it does act like a bear. Earth bears hiber­nate, and so does the celes­tial bear. It’s low in the north in win­ter and returns in spring in a way that reminded people of bears’ seasonal behavior.

What is truly interesting is that widely separated people around the world – from Europe to Asia to North America – saw these stars as a bear. We can only specu­late, but it’s likely that the concept of the Great Bear origi­nat­ed during the Ice Age and was carried from Europe to Siberia – or the other way around – and then to North America more than ten thousand years ago. If so, this name is one of the world’s oldest surviving cultural arti­facts.

Little Babylonian, and less Sumerian constellation lore remains to­day, and that which does is imbedded in the classical Greek stories. The Greeks bor­row­ed the concept of the zodiac from the Babylonians and incorporated Babylonian star stories into their own myths. Later, the Romans borrowed the Greek stories and we’ve borrowed those of the Romans, so there is a tradition of borrowing and elaborating that dates back at least 6,000 years.

We know Greek mythology in detail, but less about how they divided the sky. There are only scattered references to stars and star patterns from early Greek times.

The astronomer Ptolemy, who lived in Alex­an­dria around 150 BC, described the 48 “Ptolemaic” or classical con­stella­tions, which remained essentially unmodified for 14 centuries. Perhaps 30 of these are Babylon­ian in pedigree and the rest indigenous Greek. His main source was a long poem based on an earlier and now lost work from about 350 BC by Eudoxus – the Greek astronomer who con­struct­ed the first record­ed celestial globe and who worked out the idea of celestial coordi­nates. Ptolemy’s book became known as the Almagest (“the Great­est”) when translated into Arabic. The Arabs gave most of the stars their familiar common names, which are usually Arabic trans­la­tions of the stars’ posi­tions as describ­ed by Ptolemy. Rigel, for example, comes from Arabic for “foot,” which is exactly where the star is within Orion. Following the Dark Ages, the Almagest was trans­lated into Latin, the universal language of the Christian world, and reintroduced into Europe around the year 1,000 after an absence of nearly a millennium. The 48 Ptolemaic star patterns form the core of the constellations of the northern sky.

Many additional constellations were added during the Age of Ex­plor­ation. When European navigators first ventured into southern waters in the late 1500s and early 1600s, they discovered an unchart­ed sky in addition to uncharted lands. They divided the southern sky into groups of stars, naming the new constellations after exotic things they found in the new world, like Pavo the peacock and Indus the American Indian. Many of these new constellations achieved legitimacy and permanence by virtue of being included in Bayer’s great Urano­metria star atlas of 1603. (Bayer also introduced the idea of using Greek letters to name the brighter stars in this atlas.)

Seven additional constellations appeared in 1690 in a star atlas by the Polish astrono­mer Johannes Hevelius. He felt that some areas of the sky were too empty and that his atlas would look more attractive if these areas of faint stars only were filled in. His new constella­tions include Lacerta the Lizard and Vulpecula the Fox. Hevelius is remem­ber­ed today as the last astronomer to reject using the “newfangled” telescope and to observe by eye instead.

The last burst of constellation-naming is courtesy of the French astron­omer Nicolas Louis de Lacaille, who lived in Cape Town, South Africa, from 1750-1752. He created 14 new constel­la­tions from the southern stars, naming them after prac­ti­cal objects like an air pump, a chisel, a micro­scope, and a pendulum clock. This may not seem romantic to us, but appar­ent­ly these were fasci­nat­ing objects in their time, and now they too are immortaliz­ed in the sky. They contrast so greatly with the mythological beasts and heroes of the classical age that Lacaille has been accused of turning the sky into someone’s attic.

(Images micro.bmp and tele.bmp Caption: “Telescopium and Microscopium, two of the Southern constellations named after technological objects”)

Defunct Constellations

Not all constellations are ancient. Although the last wave of constel­la­tion-inventing ended when the southern sky was finally filled in the middle of the 18th century, astronomers felt free to create their own as recently as the late 1800s. Often constellations were created for politi­cal purposes – to flatter a patron, for example – but such contri­vances were seldom accepted graciously by other astronomers, and most dis­appeared as quick­ly as they appeared. They now are minor foot­notes in the his­tory of the sky. Examples include Robur Carolinium, or Charles’ Oak, invented by Edmond Halley to honor King Charles II (who once escaped death by hiding in an oak tree); Frederick’s Glory, a sword that honored Prus­sia’s Frederick the Great; and Telescopium Herschelli or Her­schel’s Telescope.

Through the 18th century, there was no universally approved list of constellations and no official constellation bound­aries. Mapmakers were free to add new constellations if they wished and to decide where one con­stellation ended and another began. This situation was intolerable to astronomers, who were creating ever-more detailed star charts, and an early task of the new International Astronomical Union was to settle the constellation boundary question once and for all. A commission was appointed to draw up a list of official con­stel­lations and to define their boundaries, and the commission’s results were approved in 1928. The boundaries are a series of “straight lines” in the sky that read like legal property boundaries on earth. Since 1928, no new constellations have been invented.

The Official Cygnus

Cygnus may look like a cross or even a swan, but the actual con­stel­lation includes many fainter stars that lie outside the popular stick figure. Since 1928 a constellation has been defined in the same way that a parcel of property is described on earth – by speci­fying its boundaries as a series of interconnected straight lines. The true definition of Cygnus is everything in the sky that lies within these boundaries (the middle two-thirds of the description is omitted):

  • Méridien de 19 h. 15 m. 30 s. de 27° 30′ à 30° 0′
  • Paralléle de 30° 0′ de 19 h. 15 m. 30 s. à 19 h. 21 m. 30 s.
  • Méridien de 19 h. 21 m. 30 s. de 30° 0′ à 36° 30′ m
  • Paralléle de 36° 30′ de 19 h. 21 m. 30 s. à 19h. 24 m.
  • Méridien de 19 h. 24 m. de 36° 30′ à 43°
  • Paralléle de 28° 0′ de 21 h. 44 m. à 21 h. 25 m.
  • Paralléle suite de 28° 0′ de 21 h. 25 m. à 20 h. 55 m.
  • Méridien de 20 h. 55 m. de 28° 0′ à 29° 0′
  • Paralléle de 29° 0′ de 20 h. 55 m. à 19 h. 40 m.
  • Méridien de 19 h. 40 m. de 29° 0′ à 27° 30′
  • Paralléle de 27° 30′ de 19 h. 40 m. à 19 h. 15 m. 30 s.

(Reference: Délimitation Scientifique des Constellations, E. Delporte, Cambridge, 1930.)

Constellations of Other Cultures

Our familiar constellations are a product of the history of our west­ern cul­ture. Today, the 88 constellations we know and love are univer­sally recog­nized. Like our Gregorian calendar, they are “official” around the world. But it was not always so, and each culture invented its own way of dividing the sky. Sadly, the indigenous constellations of most cul­tures have been lost and only in scattered remote areas are pre-western con­stella­tions still remember­ed.

The ancient Egyptians saw a Crocodile, Hippopotamus, the front leg of a bull (our Big Dipper), and the god Osiris (our Orion). Their Isis is our Sirius – an important goddess whose reappearance was used to predict the annual flood of the Nile. The original Egyptian constella­tions were re­placed by the familiar Greek constellations after Egypt was conquered by Alex­ander the Great in the third century BC, and in the following centuries their ancient knowledge was almost completely lost. The only clues that remain of ancient Egyptian sky lore comes from enigmatic tomb paint­ings.

The Chinese divided the ecliptic into 28 lunar mansions, somewhat analogous to our zodiac (which is solar), and the stars into almost 300 groupings that are smaller than our constellations and that we would call asterisms. Some patterns that look so obvious to us that we have a hard time seeing them any other way, like the W of Cas­siopeia, are subdivided by the Chinese (in the case of Cassiopeia, into three). They have four seasonal “super-constellations,” each made of several asterisms with a similar theme: the White Tiger of autumn, the Black Tortoise of winter, the Blue Dragon of spring, and the Red Bird of summer (illustrations of 4 Chinese super constellations?). The Chi­nese paid less attention to star bright­nesses than we do when dividing the sky and they incorporated fainter stars. We are amazed that Lynx is an official constellation, so faint are its stars, but the Chinese regularly in­cluded such faint stars in their asterisms. Among the Chinese constella­tions are the Dogs, the Awakening Serpent, the Wag­ging Tongue, the Tortoise, the Army of Yu-Lin, the Weaver Maid, and the Cow Herd­er.

Peruvian Dark Constellations

The Inca of pre-conquest Peru recognized what we may call “dark constella­tions.” At their southern latitude, the center of the Mil­ky Way passes straight overhead and is spectacular. They recognized patterns of bright stars like we do, but they also named the dark dust clouds of the Milky Way. They thought of the dark clouds as earth carried to the sky by the celestial river. Among the dark clouds were Ya-cana the Llama and her baby Oon-yalla-macha, the fox A’-toq, the bird Yutu, and Hanp-á-tu the Toad. The Indians watched for changes in the visi­bility of the dark clouds, caused by upper-atmospheric mois­ture, that would tell them whether the coming year would be wet or dry.

The Changing Constellations

Remember that constellations are areas of the sky, and they have infinite depth, so the stars in a constellation do not necessarily have any­thing to do with each other, although they appear to lie in approximate­ly the same direction as seen from earth. Two stars that appear to be very close to each other may actually be separat­ed by enormous distances, one far beyond the other, while stars on opposite sides of the sky may be rela­tively close to each other with us in the middle. You cannot tell just by look­ing. This third dimension of depth means that the appearance of the constellations depends on your vantage point.

Distances within our solar system are so small that the constellations look exactly the same from Mars, Venus, and Pluto. But if we move far beyond our solar system, the story changes. If our earth orbited a distant star rather than our sun, the stars would be distributed in completely different patterns and our familiar con­stel­lations would not exist. If aliens live on other planets in orbit around other stars, they have their own constella­tions.

Interstellar Exploration

In addition to all the other adjust­ments that come with moving into a new home, humans of the future who colonize planets around other stars will have the task of dividing their sky into their own constel­la­tions. It will be a lot of fun.

One of the nearest stars to Earth which we may visit is Barnard’s Star, about six light years distant. Open the file “Barnard” to see that the new immigrants would see a bright 0th magnitude star near the belt of Orion which is not in our night sky – because it is our own sun!

Even when viewed from earth, the constellations are not forever. Each star in the sky is actually in motion. Although these speeds are quite high (most stars at moving at several hundred kilometres per second!), the vast distance to the stars mean that this motion is imperceptible to us. Each star’s speed and direction is different from its neighbors, causing each star to move relative to its neighbors as seen from earth, over very long periods of time. This very slow motion of a star across the celestial sphere is called its proper motion (“proper” mean­ing “belonging to,” rather than “cor­rect”). Each star’s info in the RASC’s Observer’s Handbook shows that star’s proper motion in terms of the amount by which a star’s RA and Dec will change each year. (Remember that a star’s RA and Dec will also change due to precession, but precession changes the positions of all stars equally.)

Our familiar constellations look much the same now as they did at the end of the last Ice Age, but in the distant future they will become distorted by their stars’ motions and eventually they will become unrecog­nizable. The constellations of 1 million AD will bear no resemblance what­soever to the star patterns we know and love today. Eventually people will have to invent new constellations. It would be interesting to know how long people will retain the classical constellations as they become increasingly distorted before revising the scheme and starting over.

The Big Dipper 100,000 Years from Now

The Big Dipper really does look like a dipper, but it won’t always. The middle five stars are traveling together through space on nearly parallel paths as they orbit around the center of the Milky Way, and they will retain their relative spacing far into the future. The Dipper’s two end stars, however, are traveling in the opposite direction. Eventu­al­ly the Big Dipper will become stretched into what people may one day call the Big Lounge Chair.

Source: Starry Night