1901 Annie Jump Cannon constructed this classification:
| Class | Temperature in K | Color |
|---|---|---|
| O | >= 30000 | blue |
| B | 10000 – 30000 | blue white |
| A | 7500 -10000 | white |
| F | 6000 – 7500 | yellow white |
| G | 5200 – 6000 | yellow |
| K | 3700 – 5200 | light orange |
| M | 2400 – 3700 | orange red |
Mnemoic: Oh, Be A Fine Galaxy, Kiss Me
