We classify stars based on their spectra. The sequence of spectral classes in essence tells us the temperature of the star. From hottest to coolest the classes are O, B, A, F, G, K, M.
@evilscientistca So back in the 1920 stars were classified based on the prominence of H-beta Balmer absorption line ― alphabetically, from the most prominent ‘A’ to the least ‘O’.
Annie Jump Cannon projected those A,…,O scale to the temperature based OBAFGKM (missing classes were too close to other classes and were dropped), where the surface temperature smoothly decreases from O to M.
The new scale preserved old names, but at the cost of losing relation between them.
Damn trade-offs!
@evilscientistca and BTW
Only Bad Astronomers Forget Generally Known Mnemonics
@kmicu Though I prefer Anne Jump Cannon's Mnemonic...
@kmicu had the advantage of not having to re-classify 10s of thousands of stars though.
@evilscientistca we could introduce a second scale e.g. from 1 to 7 and gradually migrate to it. No need to re-classify anything e.g. “Some star is 2-class of brightness (B in the deprecated classification).”
Britain managed to move from inconsistent imperial to metric system so _anything_ is possible 😺
For *me* consistency and accessibility for _newcomers_ is more important than keeping a confusing scale, because we, old timers, are comfortable/familiar with it.
@evilscientistca With the mnemonic:
Oh
Be
A
Fine
Girl
Kiss
Me