Constellation Connectivity Lines
Constellation Connectivity Lines
| Group Name | constel |
| Reference | -- |
| Prepared by | Brian Abbott, Carter Emmart (AMNH/Hayden) |
| Labels | Yes |
| Files | constellations.speck, constellations.label |
| Dependencies | none |
| Census | 88 constellations and labels |
Astronomers divide the sky into 88 regions called constellations. Today we know the stars in any given constellation do not necessarily have any physical relationship with one another. One star may be nearby, while an adjacent star may be far away. These regions were defined around pre-existing figures invented by our ancient ancestors. Stars in the shape of a man, woman, beast, or the occasional inanimate object were part of an oral tradition that was passed from generation to generation.
Throughout history, artists have drawn pictures over star maps to represent these figures—a bull for Taurus, a dragon for Draco, and a bear for Ursa Major. More often, though, we see “stick figures,” or lines connecting stars, that form the constellation figures.
History of the Constellations
While most civilizations interpreted the heavens independently of one another, today the International Astronomical Union accepts 88 constellations, based mainly on Babylonian and Greek mythology and lore. More than half of the 88 constellations that became official in 1930 were known to the ancients.
Some of the Greek constellations appear in the poetry of Homer from the 9th century B.C. Around the 5th century B.C., the Babylonians identified the ecliptic—the path that the Sun, Moon, and planets appear to follow throughout the course of the year—and divided it into the 12 parts of the zodiac.
In the 2nd century B.C., the Egyptian astronomer Ptolemy cataloged information on 1,022 stars grouped into 48 constellations. His work, the Almagest, remained the authority on the constellations until the 16th century, when European explorers voyaged into southern latitudes.
Once exploration of the Southern Hemisphere and its sky began, constellations were added quickly. In 1603, Johann Bayer published the first star atlas, which included 12 new constellations in the southern sky. Throughout the 17th century, an effort to depaganize the heavens led to the creation of the constellation Crux from bright stars that Ptoloemy had considered to be part of Centaur. Additionally, Ptolemy's grand constellation Argo Navis (Argo the Ship) was divided into the ship's keel (Carina), its stern (Puppis), and its sails (Vela).
Changes were made throughout the 18th century and into the 19th century. In 1875, boundary lines for the constellations were drawn along lines of right ascension and declination. These boundaries and the constellations themselves were adopted by the International Astronomical Union in 1930 and provide great simplification to the night sky. Now each star, planet, comet, and nebula—all objects in the night sky—belongs in one of these 88 regions.
Constellation Connectivity Lines
In the Atlas, we represent the constellations by connecting the main stars that make up the constellation “stick figures,” as seen from Earth. We generate the lines by connecting a series of (x, y, z) points using Partiview's mesh command. To avoid some lines appearing twice as bright, some constellations are formed with several meshes so that lines do not overlap.
While there are many philosophies on how to connect the stars, we have chosen configurations that we are comfortable with. Some people swear by the constellation art by author H. A. Rey, others by their favorite star atlas.
Each constellation has a label that is positioned within the constellation and placed arbitrarily at 65 light-years from Earth.
Configuring the Lines and Labels
The constellation lines and labels can be configured if their colors or brightnesses do not suit you. The colors are set in the mw.cf file with these commands:
eval cment 1 0.6 0.4 0.4
eval cment 2 0.8 0.0 0.0
eval cment 3 0.0 0.3 0.8
eval textcment 1 0.6 0.2 0.2
eval alpha 0.4
The cment command sets the red-green-blue colors of color indexes 1, 2, and 3. The textcment command sets the color of the labels. If you would like to change these colors, simply edit mw.cf or change them interactively at the Partiview command line (where you don't need the eval prefix).
The brightness of the lines is set with the alpha command. An alpha of 1 sets the transparency of an object to be completely opaque (brightest), while a value of zero sets complete transparency (invisible). You can use the Alpha Slider to adjust this interactively. We don't recommend setting the alpha value to 0 or 1, as the lines are invisible at 0 and completely opaque at 1, often producing unwanted graphics effects.
If you would like to see only one or several constellations, consider forming a new group and pulling out those constellation meshes you want to see into a new file. You can also set the color for a color index to (R, G, B) = (0, 0, 0) (black), rendering those constellations invisible.
© 2002-2005 American Museum of Natural History
Last Modified: 2007-12-19 by Brian Abbott