This is in reference to the Hertzsprung-Russell Diagram?

Question

What is the significance of O B A F G K W???

Answer 1

When it was discovered that starlight's spectra had lines, the first attempts to classify the stars was according to the intensity of certain (specific) lines. Categories were simply labeled A, B, C, D... down the alphabet.

When H and R came along and found that
1- you could classify stars by temperature and get a nice graph, and
2- you can classify stars by mass and get the same nice graph.

The H-R diagram was born. It was then discovered that the hottest stars did not have the lines used in the previous system (too hot), and the 'colder' stars also did not have the lines (too cold). However, the stars' spectra were already clasisfied using the letter system.
So, they kept the letters but rearranged them so that they would come in the order of temperature (or mass, as you prefer).
That is why the order is now the way it is.

Answer 2

on condition that all and sundry replied with the oh be a great woman kiss me right this is what the letters recommend : each and each letter corresponds to a undeniable sort of spectrum, and for this reason shade, of a great call. The letters additionally correspond sort of to the temperatures, with O, the bluest, being the maximum popular. O Stars are warm, blue, and great. B Stars are additionally warm, blue, and great. A stars have the best Hydrogen traces of any sort. they are particularly cooler F colour is white with a reasonable tinge of yellow. G is cooler with a crimson orange ..basically like our sunlight ok are orangish stars that are particularly cooler than our sunlight M are crimson dwarfs

Answer 3

That's a memory trick for remembering the sequence of star classifications. You're off a little with the sequence you wrote :: O B A F G K M is the correct sequence. You can remember that sequence by "Oh Be A Fine Girl Kiss Me."