Stellar classification facts for kids
In astronomy, stellar classification is a way of grouping stars by temperature. Star temperature can be measured by looking at its light spectrum, color which the star shines.
Stars are also grouped into spectral types or classes by color.
In general, a star's temperature determines its color, from red to blue-white. Spectral types are named with a letter. The seven main types are M, K, G, F, A, B and O. M stars are the coldest stars and O stars are the hottest. The full system contains other types that are hard to find: W, R, N, and S.
The closest star to the Earth, the sun, is a class G star.
Contents
Harvard spectral classification
| Class | Surface temperature (kelvin) |
Conventional color description |
Actual apparent color | Mass(solar masses) | Radius(solar radii) | Luminosity (bolometric) |
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 | blue white | deep blue white | 2.1–16 M☉ | 1.8–6.6 R☉ | 25–30,000 L☉ | Medium | 0.13% |
| A | 7,500–10,000 K | white | blue white | 1.4–2.1 M☉ | 1.4–1.8 R☉ | 5–25 L☉ | Strong | 0.6% |
| F | 6,000–7,500 K | yellow white | white | 1.04–1.4 M☉ | 1.15–1.4 R☉ | 1.5–5 L☉ | Medium | 3% |
| G | 5,200–6,000 K | yellow | yellowish white | 0.8–1.04 M☉ | 0.96–1.15 R☉ | 0.6–1.5 L☉ | Weak | 7.6% |
| K | 3,700–5,200 K | orange | pale yellow orange | 0.45–0.8 M☉ | 0.7–0.96 R☉ | 0.08–0.6 L☉ | Very weak | 12.1% |
| M | 2,000–3,700 K | red | light orange red | ≤ 0.45 M☉ | ≤ 0.7 R☉ | ≤ 0.08 L☉ | Very weak | 76.45% |
| R | 1,300–2,000 K | red | red | Unknown | Unknown | Unknown | Very weak | Unknown |
| N | 1,300–2,000 K | red | red | Unknown | Unknown | Unknown | Very weak | Unknown |
| S | 1,300–2,000 K | red | red | Unknown | Unknown | Unknown | Very weak | Unknown |
The mass, radius, and luminosity listed for each class are appropriate only for stars on the main-sequence portion of their lives and so are not appropriate for red giants.
The spectral classes O through M are subdivided by Arabic numerals (0–9). For example, A0 denotes the hottest stars in the A class and A9 denotes the coolest ones. The Sun is classified as G2.
The Hertzsprung-Russell diagram is more often used in astronomy, because it relates three important variables: the absolute magnitude, the luminosity and the surface temperature. It is as important to astronomy as the periodic table is to chemistry.
Conventional and apparent colors
The conventional color descriptions are traditional in astronomy, and represent colors relative to the mean color of an A-class star which is considered to be white. The apparent color descriptions are what the observer would see if trying to describe the stars under a dark sky without aid to the eye, or with binoculars.
The Sun itself is white, though it is sometimes called a yellow star.
Related pages
Images for kids
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Montage of false color spectra for main-sequence stars
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Guide for Secchi spectral types ("152 Schjellerup" is Y Canum Venaticorum)
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Proper motion of stars of early type in ± 200,000 years
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The movement of stars of late type around the apex (left) and antapex (right) in ± 200,000 years
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The spectrum of an O5V star
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B-class stars in the Jewel Box cluster (Credit: ESO VLT)
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Class A Vega (left) compared to the Sun (right)
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The Sun, a G2 main-sequence star, with dark sunspots
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UGC 5797, an emission-line galaxy where massive bright blue stars are formed
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Hubble Space Telescope image of the nebula M1-67 and the Wolf–Rayet star WR 124 in the center
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Artist's impression of an L-dwarf
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Artist's impression of a T-dwarf
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Artist's impression of a Y-dwarf
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Image of the carbon star R Sculptoris and its striking spiral structure
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Sirius A and B (a white dwarf of type DA2) resolved by Hubble
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