Courtesy of Curiosity.com:
“You might have heard the expression: “Oh! Be A Fine Girl/Guy – Kiss Me!” It’s an easy pneumonic device to remember the ranking system of the stars, and we have Annie Jump Cannon to thank for it. While working as a computer at Harvard in the 1890s, Cannon came up with what is now called the Harvard system of stellar classification, ranking stars as O, B, A, F, G, K or M. “Cannon simplified two earlier schemes into one that astronomers still use today. Her classification had just seven letters arranged by decreasing temperature: OBAFGKM, according to Air and Space Smithsonian. “Over the course of her life, Cannon classified the spectra of over 350,000 stars—legend has it that she could look at any stellar spectra and classify it in just three seconds””
- Originally, stars were classified based on a brightness rating, with one being very bright and 5 being very dim.
- Temperature is one of the most important properties to consider when classifying.
- The Earth’s sun ranges right in the middle of temperature, mass and brightness when compared to other stars we know of.