Hard Lessons | The Writing Site of R K Athey

Stellar Classification

400px-HR-diag-no-text-2.svgThe following article won’t mean much to anyone not interested in star classification. I’m working on a randomized star sector generator to help give setting information for my space mercenaries universe.  Below are a few links I’ve created to investigate astronomy and astrophysics.

Astronomers classified stars through an arcane system of letters and numbers. Most stars are classified using the letters O, B, A, F, G, K, and M. The order of the letter indicates relative temperature. O is the hottest star and M is the coolest. There are various mnemonics for remembering the order. The one I learned was “Oh Be A Fine Girl, Kiss Me”. There are others.

According to informal tradition, O stars are called “blue”, B stars are “blue-white”, A stars are “white”, F stars are “yellow-white”, G stars are “yellow”, K stars are “orange”, and M stars are “red”. Our star, Sol, is a G class star.

Stars are further classified by a Roman numeral depicting size. Type I is a super giant. Type III is a giant. Type V is a dwarf. Our Sun is a GV meaning a Yellow Dwarf star. Dwarf stars are also known as Main Sequence stars and they make up most of the stellar population.

Finally, stars have another number running from 0 to 9. 0 is the hottest and 9 is the coolest. Sol is a G2V, or a medium hot yellow dwarf.

270px-H-R_diagram.svgBelow are some links I used for my stellar generator.

A nice article about Astronomy in general


Here’s a link with more about stars


And finally Wikipedia – the font of all knowledge


  • O 0.00003%
  • B 0.125%
  • A 0.625%
  • F 3.03%
  • G 7.5%
  • K 12%
  • M 76%
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