Stellar classification (astrophysics): Difference between revisions
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Revision as of 23:54, 25 October 2007
Stars are classed by various properties. A common classification is surface temperature. Beginning with early spectral schema in the 19th century ranking stars from A to P, the spectral classification, called “Morgan-Keenan spectral classification” [1][2] now ranks stars in seven main types: O, B, A, F, G, K, M.[3] Each spectral classification is further divided into tenths. Our sun, Sol is a G2.
Classification system
The stars are ranked from hottest to coldest:
| Class | Temperature | Conventional vs Apparent color | Characteristics | Mass [6] | Radius [7] | Luminosity [8] | Hydrogen lines | % of all MSSs[9][10] |
|---|---|---|---|---|---|---|---|---|
| O | 30,000–60,000 K | blue/blue | Ionized He & metals;
weak H |
60 M☉ | 15 R☉ | 1,400,000 L☉ | Weak | ~0.00003% |
| B | 10,000–30,000 K | blue white/blue white to white | Neutral He, ionized metals, stronger H | 18 M☉ | 7 R☉ | 20,000 L☉ | Medium | 0.13% |
| A | 7,500–10,000 K | white/white | Balmer H dominant, singly-ionized metals | 3.1 M☉ | 2.1 R☉ | 80 L☉ | Strong | 0.6% |
| F | 6,000–7,500 K | yellowish white/white | H weaker, neutral & singly-ionized metals | 1.7 M☉ | 1.3 R☉ | 6 L☉ | Medium | 3% |
| G | 5,000–6,000 K | yellow/yellow | Singly ionized Ca, H weaker, neutral metals | 1.1 M☉ | 1.1 R☉ | 1.2 L☉ | Weak | 8% |
| K | 3,500–5,000 K | orange/yellow orange | Neutral Metals, molecular bands begin to appear | 0.8 M☉ | 0.9 R☉ | 0.4 L☉ | Very weak | 13% |
| M | 2,000–3,500 K | red/orange red | Ti oxide molecular lines; neutral metals | 0.3 M☉ | 0.4 R☉ | 0.04 L☉ | Very weak | >78% |
References
- ↑ Note: based on the work of Annie Cannon and other astronomers from the Harvard College Observatory
- ↑ Annie Jump Cannon 1883-1941
- ↑ A popular mnemonic for this is Oh Be A Fine Girl, Kiss Me
- ↑ The Colour of Stars. Australia Telescope Outreach and Education (December 21 2004). Retrieved on 2007-10-26. — Explains the reason for the difference in color perception.
- ↑ The Hertzasprung-Russell diagram (subsection The Harvard spectral sequence). University of Tennessee, Dept of Physics and Astronomy (unknown). Retrieved on 2007-10-26. — Details various aspects of stellar classification.
- ↑ NASA glossary Solar Mass. Earth's sun is one solar mass. Equal to about 2 X 10E30 kg or about 333,000 time the mass of the earth
- ↑ Solar Radius. Earth's sun is the standard with one solar radius equal to about 6.960 X 10E8 km. This is about twice the distance of the earth from the moon, 110 times the radius of earth, and 0.004652 AU (astronomical unit), the average distance of the earth from the sun. Solar Radius University of Oregon. The Corona Spartan 201. NASA
- ↑ Solar Luminosity. The standard is earth's sun equal to one solar luminosity. The luminosity of the sun is about 3.827 X 10E26 watts or 3.827 X 10E33 ergs
- ↑ MSS = Main Sequence Star
- ↑ LeDrew, G.; The Real Starry Sky, Journal of the Royal Astronomical Society of Canada, Vol. 95, No. 1 (whole No. 686, February 2001), pp. 32–33
- ↑ Star classification