How is a constellation chosen?

What determines that in a group of random stars, some are connected to one another to make a constellation?|||Every culture had picked their own constellations in the sky, and they're not all the same. We settled on the approximate boundaries of the system the Greeks had picked, which the International Astronomical Union formally defined.|||Throughout history people have assigned identities to star groups to guide their view of the changing sky, aid in recognizing months and seasons, and attribute religious significance. Appearance and disappearance of constellations likely signaled planting and reaping seasons for farmers, aided sailors in navigation, and guided travelers across deserts. The ascription of constellation names and stories aided memory and communication about the night sky.





Constellations recognized by astronomers today still correspond to many of those identified in ancient China and the Middle East. The oldest known drawings of constellations鈥攐n vases, official seals, and gaming boards鈥攚ere made by Sumerians (in present-day Iraq) as early as 4000 B.C. The constellation Aquarius was named by the Sumerians after An, their god of heaven. Babylon and Assyria, later civilizations in the same geographic area, inherited the Sumerians' astronomical traditions and many of their myths and legends surrounding the skies. They developed a twelve-segmented zodiac, that is, a set of twelve constellations that lie in the annual path of the sun around the earth, as well invented a degree system to distinguish positions in the sky similar to latitudes and longitudes. Knowledge of the constellations spread from Babylon to Egypt, perhaps by way of Minoans from Crete who settled in Egypt. Early Greek scholars encountered knowledge of the constellations in Egypt, and changed many Arabic names to Greek. In 150 A.D., the Greek scientist Ptolemy published a book, known by its Arabic name, Almagest, in which he described 48 constellations, of which 47 are known today by the same name. In the sixteenth century, explorers from northern lands viewed the southern skies and named new constellations.





In the early twentieth century, the International Astronomical Union added 38 constellations to the ancient groupings and drew rectangular borders around all 88, permitting astronomers to divide the sky into segments in which they can locate stars. The brighter stars typically still have Arabic names, and they have also been assigned Greek letters and Arabic numbers.





The exhibition, Starry Transit: An Installation by Martha Glowacki, presented by the Madison Museum of Contemporary Art at Washburn Observatory, was inspired by scientific research indicating that night migrating birds orient themselves by patterns of stars.|||"mnemonics"





The idea of connecting stars in groups, then giving names to the groups, then creating stories linking these "objects" together was a convenient way to memorize the location of stars and their relation (in position) to each other.





The most interesting (because it is the one that ties together the highest number of figures in very few independent stories) is Greek mythology.





Once a group of philosophers had agreed on naming groups of stars, they would teach those names and the stories that went with them, to their students.





The students would find that a convenient and efficient way to learn the position of the stars. Once they became philosophers in their own right, they would pass on the same stories (sometimes with embellishments) to their own student, and so on.





Then, someone would come along and write down the stories and that would confirm the names of the constellations. These would be passed on from town to town as the philosophers passed the books around and eventually, a whole country would agree on names for the most important constellations (for example, the zodiac) and these would they show up on star atlases.





Many of the stories and names associated with the constellations in Greek astronomy came from the Babylonians. That is why it did not take very long for everyone to settle on using the same name for a given group of stars.





One very accurate and complete star atlas was prepared by Hipparchus (around 135 BC). He is the one who labeled the stars' brilliance in a scale of magnitude; the modern scale is based on his scale. His atlas shows most of the constellations that we know today using the same names (in Greek).|||There are 88 official constellations. Both the constellations and their boundaries were determined in 1930 by the International Astronomical Union.