Sky Literacy

    Astronomy is one of the few sciences that allows for active participation by the nonprofessional. The night sky is accessible to most individuals, and it is here that an enjoyable start can be made to comprehend the beauty, as well as the history of this oldest science. Unfortunately, in many urban regions the glow of civilization has caused a dimming of our senses toward nature and a decrease in our enthusiasm to look skyward and enjoy the majesty of this natural phenomenon.
     The ability of humans to realize that the rhythmic frequencies of the heavens could serve as an accurate time monitoring device allowed for the establishment of agriculture on a more orderly basis, a division of labor among the populace, the functioning of governments, and the eventual blossoming of our technological society. The consistency of the sky, however, has had even greater ramifications than just our own personal refinement. Philosophically, it is our link to the past, for everyone who has lived within the time frame of recorded history has gazed upon the same stars and planets that we can observe today. That is an amazing amount of time by human standards, and because the sky changes so gradually, the stars and their patterns will remain a unifying element to the history of humankind tens of thousands of years into the future.
    The ancients organized the starry firmament into a series of regions -- constellations -- representing creatures, deities, and inanimate objects. Knowledge of some of these figures date back almost 5000 years. Many of these divisions were arbitrary in nature. Areas of the sky were marked off to honor a special deity; then attempts were made to produce a representative picture artificially. Even with this capricious attitude, an amazing number of constellations visible to northern hemispheric observers bear striking resemblances to the figures which they are supposed to portray.
    And, of course, there was great entertainment value in the sky. Consider the starry firmaments as the original TV set, simple to operate, and requiring no electricity. It had one channel, could only be seen on clear nights, and its program took one year to cycle through in its entirety. Yet its story potential seemed endless as witnessed by the continuation of the use of mythologies today. Consider the popular television programs of Hercules and Xena (Xena is not a constellation) or movies such as Clash of the Titans, and it is obvious that good stories endure.
     Unfortunately, the same cannot be said for the southern sky. These regions were unknown to the ancient civilizations and were first delineated by European explorers beginning in the sixteenth century. Many of the star figures deal with items familiar to the technology of that era, such as furnaces (Fornax), compasses (Circinus), air pumps (Antlia), pendulum clocks (Horologium), and telescopes (Telescopium) among others. Needless to say, the people who originated these star patterns did not possess the same richness of imagination as their predecessors, and this may be, in part, one of the reasons why the southern sky does not hold the same appeal as its northern counterpart.
     The most important group of constellations known to the ancients were those through which the seven principal deities moved: the sun, the moon, and the five naked eye planets. The Greeks named this region the zodiac (circle of animals), and it was most likely the first zone of the sky to be formalized. Astrology had its origin with the movements of the sun, moon, and planets within this tract, and much of the drama of western mythology, as it is related to the sky, was formulated around these objects.
     Eighty-eight constellation boundaries encompassing both hemispheres were officially sanctioned in 1928 by the International Astronomical Union, a worldwide congress of professional astronomers. All of the stars within a particular boundary are members of the same constellation, regardless of whether or not they are incorporated into forming the pattern. The constellation pictures have not been standardized which has led to a great deal of variations, depending upon the source. Most modern star atlases simply ignore the problem by only representing the boundaries and not the figures themselves.
     To further complicate matters, there are numerous star groupings which are considered to be constellations by the general public, but are not recognized as such by the professional community. The pattern most frequently mistaken for a constellation by Americans is the Big Dipper. It is, in essence, composed of the brightest members of the Great Bear, the constellation of Ursa Major. Such unofficial groupings of stars are termed asterisms. The Little Dipper and the Pleiades are two other examples of well-known asterisms often mistaken for constellations.
     The reason for standardizing the constellation boundaries has not stemmed from any incentive to memorialize their ancient lore, but rather as a means of rapidly identifying the region of the sky in which an object of interest is located. Since the constellation regions are large with respect to the position of individual objects, there exist more exact methods for accurately positioning a telescope so that an observer can identify a particular star or object. The primary coordinate system which is used by astronomers is termed right ascension and declination. It is earth's grid system, longitude and latitude, projected into the sky.
     Right ascension and declination allow for the precise location of everything in the heavens, and, at the very least, the numerical designation or naming of any celestial object. An example of this might be the location of a star at RA 023150.4; Dec +891551, better known to most individuals as the North Star or Polaris. Brighter stars, such as the Polestar, have proper names, usually Arabic translations, coming originally from the Greek language. There are also Greek and Latin exceptions, and Polaris happens to be one of them. It is an abbreviation from the medieval Latin, Stella Polaris or Pole Star.
     With the ascendancy of Islam during the seventh and eighth centuries AD, and its near conquest of Europe, many of the Arabic translations were brought into more common usage by western medieval astronomers. These names have been unofficially adopted by professional and amateur observers. The brightest stars in any one particular constellation also have Greek letter designations as well as Arabic numerals. This really represents a combination of nomenclature systems.
     The earliest identification system utilized upper case letters of the Greek alphabet introduced by Johannes Bayer (died 1625) in 1603. With few exceptions, stars received letters in order of descending brightness, followed by the genitive form of the constellation. Polaris, the brightest star in Ursa Minor, the little bear, was designated as alpha Ursa Minoris in Bayer's scheme. Once the 24 characters of the Greek alphabet were exhausted, Bayer repeated the procedure using first lower case letters, then the upper case letters of the Roman alphabet. John Flamsteed (1646-1719) devised an alternate method by which the positions of stars of any constellation were numbered, starting from their westernmost boundaries, in order of their increasing eastward position or right ascension. Today, it is common practice to list the brightest stars of a constellation with Bayer's Greek letters (lower case) and the fainter luminaries by their Flamsteed numbers. This can be seen in the figure of Orion, the hunter to the left.
     All of this terminology can become rather confusing, especially when one considers the variety of other objects such as variable stars, galaxies, and clusters which must be properly symbolized and identified on star charts. For the purpose of Sky Literacy this extra information has been kept to a minimum.
     The star maps selected for this unit contain only the brightest stars which are visible from an urban location, away from the direct view of distracting streetlights. The different sized dots are representative of the various magnitudes or brightnesses of the stars. Characteristic stars are designated with numbers on each chart. It should be noted that fainter stars have more positive magnitudes than the brighter stars. A star of the third magnitude is about 2-1/2 times fainter than a second magnitude star, which is about 2-1/2 times fainter than a first magnitude star. The change in light intensity between a first magnitude star and a sixth magnitude star, a difference of five magnitudes, is exactly 100. The average person can observe stars of the sixth magnitude in an environment which is not light polluted. In Sky Literacy, essentially all of the stars plotted on the charts are brighter than fifth magnitude. Each chart is also provided with an approximate scale in degrees. For easy conversion to the sky, a 12-inch ruler held at arm's length is about 30 degrees in length.
     For the moment, let us return to the nighttime sky and discover for ourselves the beauty and lore of a few prominent constellations, as well as some of the names of their brightest members. What others might be tempted to call the mysterious may then be revealed to be the same source of simple amusement and joy that once motivated earlier groups of skywatchers to look up and marvel.