Key Information
Stellar Classification
| Type | Method to Categorise Stars |
| Key Classifications | Harvard System; Morgan-Keenan System |
Learning Point
- Stars vary in size, brightness, colour and power. Categorising them helps us to understand how they relate to each other, giving us a greater understanding of each star we see in the night sky. The main way of categorising them is through the Morgan-Keenan system, which includes looking at the type of light a star produces, and what it contains within it.
Project
- Work out how the following letters should be ordered correctly, and the colour they represent:
- A, B, F, G, K, L, M, O, T, Y
- Overview
- Morgan-Keenan Classification
| Class | Effective Temperature | Vega-relative Chromacity | Chromacity (D65) | Main-Sequence Mass | Main-Sequence Radius | Main-Sequence Luminosity | Hydrogen 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 to 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 | light orange | pale yellowish orange | 0.4 – 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% |
| L | 1,300 – 2,300 K | orangish red | red | 0.07 – 0.085 M☉ | 0.088 – 0.11 R☉ | 0.00006 – 0.00031 L☉ | ||
| T | 550 – 1,300 K | red | deep red | 13 – 65 MJ | ||||
| Y | < 500 K | deep red | deep red | 9 – 25 MJ |
Fun Facts
- In the 1860s the Italian astronomer Angelo Secchi distinguished four main spectral types of stars.
- The types were rearranged in a non-alphabetic sequence to put them in order by surface temperature.
- Grades I (for supergiants), II (bright giants), III (normal giants), IV (subgiants), and V (main sequence, or dwarf, stars)
- The Sun, a yellow dwarf star of some 5,800 K, is designated G2 V.
Past Lessons
| 82 | March 11, 2024 | (North America) |