- It is a kind of Metric.
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Stellar Data: The data is provided in 2 parts:
- Morgan-Keenan Spectral Type
- Yerkes Spectral Classification
Thus, when stellar data is provided in SEC file format as "M0 III A4 D M4 V", that data can be interpreted as:
- M0 III: Luminous Red Giant.
- A4 D: White dwarf star.
- M4 V: Red dwarf star.
Likewise, you could read "G2 V K2 V" as:
- G2 V: Sol-class "yellow" main-sequence star
- K2 V: Orange-yellow main-sequence star, similar to Beta Centauri.
Information on Stellar Spectral classifications has been summarized below for convenience.
Morgan-Keenan Spectral Type
- Class O:: Very hot and very luminous, being bluish in color; in fact, most of their output is in the ultraviolet range. These are the rarest of all main sequence stars, constituting as few as 1 in 3,000,000 in the solar neighborhood O-stars shine with a power over a million times our Sun's output. Because they are so huge, class O stars burn through their hydrogen fuel very quickly, and are the first stars to leave the main sequence.
- Class B:: Extremely luminous and blue. As O and B stars are so powerful, they only live for a very short time, and thus they do not stray far from the area in which they were formed. These stars tend to cluster together in what are called OB associations, which are associated with giant molecular clouds. The Orion OB1 association occupies a large portion of a spiral arm of our galaxy and contains many of the brighter stars of the constellation Orion. They constitute about 1 in 800 main sequence stars in the solar neighborhood.
- Class A:: Amongst the more common naked eye stars, and are white or bluish-white. They comprise about 1 in 160 of the main sequence stars in the solar neighborhood.
- Class F:: These stars' color is white with a slight tinge of yellow. These represent about 1 in 32 of the main sequence stars in the solar neighborhood.
- Class G:: The best known, if only for the reason that Sol (Terra) is of this class. Supergiant stars often swing between O or B (blue) and K or M (red). While they do this, they do not stay for long in the G classification as this is an extremely unstable place for a supergiant to be. G stars represent about 1 in 13 of the main sequence stars in the solar neighborhood.
- Class M:: By far the most common class. At least 80% of the main sequence stars in the solar neighborhood are red dwarfs such as Proxima Centauri. M is also host to most giants and some supergiants such as Antares and Betelgeuse , as well as Mira variables. The late-M group holds hotter brown dwarfs that are above the L spectrum. This is usually in the range of M6.5 to M9.5.
Yerkes Spectral Classification
- I - VII: These Roman Numeral designations refer to the overall class of star in terms of size.
- 0 Hypergiants
- I Supergiants
- Ia-0 Extremely luminous supergiants
- Ia Luminous supergiants, Example: Deneb (spectrum is A2Ia)
- Iab Intermediate luminous supergiants
- Ib Less luminous supergiants; Example: Betelgeuse (spectrum is M2Ib)
- II Bright giants
- III Normal giant stars
- IV Subgiant stars
- V Main sequence stars (dwarfs)
- VI Subdwarf stars (rarely used)
- VII White dwarfs (rarely used)
Other Classification Codes
- D White Dwarf (rarely used)
The early Terrans were able to institute their stellar cartographic systems after they established the Rule of Man. Most astronavigators, travelers, and spacers possess training in the previously dominant Vilani systems, but they are rarely used anymore outside of contemporary Vilani Space.
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