#astronomy 

The Harvard spectral classification system is a one-dimensional [[Star|star]] classification scheme by astronomer Annie Jump Cannon in collaboration with Edward C. Pickering

## Scale
| **Class** | **Effective temperature** | **Vega-related chromaticity** | **Chromaticity**      | **Main-sequence mass (solar masses)  <br>(solar masses)** | **Main-sequence radius (solar radii)** | **Main-sequence luminosity  <br>(bolometric)** | **Hydrogen  <br>lines** | **Fraction of all main-sequence stars** |
| --------- | ------------------------- | ----------------------------- | --------------------- | --------------------------------------------------------- | -------------------------------------- | ---------------------------------------------- | ----------------------- | --------------------------------------- |
| O         | ≥ 33,000 K                | blue                          | blue                  | ≥ 16 M☉                                                   | ≥ 6.6 R☉                               | ≥ 30,000 L☉                                    | Weak                    | 0.00003%                                |
| B         | 10,000–33,000 K           | bluish white                  | deep bluish white     | 2.1–16 M☉                                                 | 1.8–6.6 R☉                             | 25–30,000 L☉                                   | Medium                  | 0.12%                                   |
| A         | 7,300–10,000 K            | white                         | bluish white          | 1.4–2.1 M☉                                                | 1.4–1.8 R☉                             | 5–25 L☉                                        | Strong                  | 0.61%                                   |
| F         | 6,000–7,300 K             | yellowish white               | white                 | 1.04–1.4 M☉                                               | 1.15–1.4 R☉                            | 1.5–5 L☉                                       | Medium                  | 3.0%                                    |
| G         | 5,300–6,000 K             | yellow                        | yellowish white       | 0.8–1.04 M☉                                               | 0.96–1.15 R☉                           | 0.6–1.5 L☉                                     | Weak                    | 7.6%                                    |
| K         | 3,900–5,300 K             | light orange                  | pale yellowish orange | 0.45–0.8 M☉                                               | 0.7–0.96 R☉                            | 0.08–0.6 L☉                                    | Very weak               | 12%                                     |
| M         | 2,300–3,900 K             | orangish red                  | light orangish red    | 0.08–0.45 M☉                                              | ≤ 0.7 R☉                               | ≤ 0.08 L☉                                      | Very weak               | 76%                                     |
Common mnemonic: "**O**h, **B**e **A** **F**ine **G**uy: **K**iss **M**e"

Frequently used with the [[Yerkes spectral classification]].