One of the mysteries of the English language finally explained.
The group in which a star is classified according to its spectrum, especially using the Harvard classification.
- ‘Fomalhaut is only moderately Sun-like; its spectral class is A 3 Va, it's 1.7 times the Sun's diameter, has 2.3 times its mass, and is 13 times as bright.’
- ‘Suppose we wanted to find one like the Sun: say, between spectral types F5 and K5, not part of a double or multiple system, and at least a billion years old (to let things settle down a bit).’
- ‘Such an association is named ‘OB’ because these stars have O and B spectral types.’
- ‘The spectral classes O and B are subdivided into numbered subclasses by stellar mass and surface temperature.’
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