2.4 Chart Symbology

To understand the astrogation maps, it is necessary to have a working knowledge of the various symbols used. On each chart is a block titled “Map Symbols,” which is divided into three sections: symbols describing natural objects, those indicating artificial objects, and a star symbol key.

The size of star symbols on the astrogation maps indicates the absolute magnitude of the system’s primary star, the larger the circle, the greater the absolute magnitude, or brightness, of the star. A range of magnitudes from -5 to +9 is shown, and it should be remembered that negative magnitude stars are brighter than positive magnitude stars. This reverse scale is the result of an arbitrary assignment by Terran ancients of bright stars as “first magnitude”; dimmer stars were called second magnitude, third magnitude, and so on. Later, when stars brighter than those of the first magnitude were discovered, they were given negative magnitudes. The difference in brightness between any two magnitudes is a factor of about 2.5; for example, a third magnitude star is 2.5 times brighter than a fourth magnitude star. To provide some basis for comparison, Rigel is a very bright negative seventh magnitude star, and Sol is a rather dim fifth magnitude star—about 1/40,000 as bright as Rigel. Most stars fall in the range of 0 to +15, and the extreme range for normal stars is -10 to +19.

The color of the star symbols indicates the spectral color of the star, and identifies its spectral class according to the letter system currently in use. Each letter identifies a certain temperature and color, ranging from blue-white (spectral class O) to red (spectral class M). Most inhabited star systems fall into the range F-G-K, mostly yellow and bright orange stars, but a limited zone habitable under Class M† environmental standards may exist around stars of any spectral color. Binary (double), trinary (triple), and variable stars are also indicated on the maps. Three special symbols are used to mark so-called stellar corpses: novae, neutron stars, and black holes. These objects should be given a wide berth, as all three broadcast a great deal of lethal radiation.

Several lines of data are given for each star on the maps, following the arrangement shown in the star symbol key. The first line, located above the star, gives its most common name, or if the star is not well-known, the star’s number in the United Federation Catalog (UFC number). The next line lists any alternate names for the star, usually the astronomical name based on Earth’s (or in some cases, Vulcan’s) constellations: e.g., Alpha Centauri, 40 Eridani, b Vela. These astronomical names are set in lower-case type to distinguish them from local or common names, which are given in upper-case. The line located below the star gives the total number of planets in the system, and then the planet numbers of any Class M or other important planets. Additional data on these planets may be found in the appendix to this manual.

Artificial objects—star bases, deep space stations, and outpost monitoring stations—are also identified on the maps by their call signs. Major space lanes, the primary routes between inhabited star systems, are indicated on the first two astrogation maps. The two quadrant maps (charts C and D) outline the patrol routes of Constitution class starships and the communications lanes in the Interstellar Communications Network (ICN). These communications lanes must be avoided, as a passing ship may disrupt transmission and will risk damage by the high-energy beams. Certain star systems and regions of space have been marked on the charts as danger areas, and should be avoided by all vessels. If further information is required, consult the Space Operations Handbook or your navigation computer.