7 Types of Stars and Their Characteristics

At the start of the 20th century, astronomer Annie Jump Cannon organized stellar spectra into seven clear classes — O, B, A, F, G, K and M — a sequence astronomers still use today. That tidy ordering, often written OBAFGKM, is more than a cataloging trick: it encodes a star’s temperature, color, and behavior.

This article covers the 7 types of stars and what sets them apart. Why care? Stars set the stage for planets, make the elements in your body, and drive the evolution of galaxies. Below I describe each major class, give defining numbers (temperature, mass, luminosity, lifespan), name notable examples, and point to why each group matters scientifically. For spectral-class basics and stellar lifecycles, see NASA’s overview of stars.

Hot, Massive Stars

These are the brightest, hottest, and shortest-lived stars. They shine in blue-white hues, drive powerful stellar winds, and inject energy and heavy elements into their surroundings.

Typical properties: surface temperatures are very high, masses range from many times the Sun’s mass up to the most extreme stars known, and luminosities can be thousands to millions of times solar. Lifespans are brief in astrophysical terms — usually just a few million years — but their impact is large: they create H II regions, sculpt nebulae, and seed the interstellar medium through supernovae and winds (see ESA on massive stars).

Because they’re rare but powerful, hot, massive stars trigger further star formation by compressing nearby gas and serve as tracers of recent starbursts in galaxies. Examples to keep in mind include R136a1 — one of the most massive stars known — and bright O/B members like Gamma Velorum or Zeta Puppis.

1. O-type stars — Extremely hot, blue, and massive

O-type stars occupy the hot end of the spectral sequence. Surface temperatures typically exceed 30,000 K and masses are commonly above 16 M☉; in extreme cases luminosities reach up to about a million times the Sun’s.

Spectra show strong ionized helium lines and relatively weak hydrogen compared with cooler classes. They form in the densest parts of young clusters and OB associations and live only a few million years (roughly 3–10 million years for many O stars).

Notable examples are Zeta Puppis (Naos), a nearby luminous O star, and R136a1 in the Tarantula Nebula, a record-holder for extreme mass. O stars are key progenitors of core-collapse supernovae and primary sites of heavy-element production.

2. B-type stars — Very hot and luminous, but less extreme than O

B-type stars are a step cooler and generally less massive than O-types. Surface temperatures sit roughly between 10,000 and 30,000 K and masses run from about 2.5 to 16 M☉.

Spectral signatures include neutral helium plus strong hydrogen absorption lines. Lifespans span tens to a few hundred million years, so they stick around far longer than O stars but still evolve quickly compared with Sun-like stars.

Rigel (Beta Orionis) is a famous B-type example — a bright blue supergiant with luminosity around 100,000 L☉ (estimates vary with model) and a mass in the high teens of solar masses. B stars supply ionizing radiation in star-forming regions and sometimes become blue giants or supergiants; their intense light and winds make planetary habitability difficult close in.

Intermediate Stars (White to Yellow-White)

Between the hot blue stars and cool red dwarfs lie the A-, F-, and G-type stars. These intermediate classes include many of the brightest stars in our sky and dozens of well-studied exoplanet hosts.

They cover a wide span of temperatures and lifespans: A-types live for hundreds of millions of years, F-types for a few billion, and G-types (like the Sun) roughly ten billion years on the main sequence. Because they’re bright in visible light and often nearby, A–G stars serve as calibration standards and prime targets for planet searches (see the NASA Exoplanet Archive for mission data).

In short, these stars bridge the extremes: they’re hot enough to be bright and simple to observe, yet cool and long-lived enough to host stable planetary environments in some cases.

3. A-type stars — White, hot, often fast rotators

A-type stars have surface temperatures around 7,500–10,000 K and masses near 1.4–2.5 M☉. Their spectra show very strong hydrogen absorption lines, making them spectrally straightforward.

Vega (A0V) is the classic example: roughly 9,600 K and about 40 L☉. Many A stars rotate quickly and some host debris disks, which makes them useful for studying planet formation and circumstellar material. Typical lifespans are on the order of a few hundred million years.

4. F-type stars — Yellow-white, moderate temperature

F-type stars sit at roughly 6,000–7,500 K with masses around 1.0–1.4 M☉. Their hydrogen lines are weaker than A-types and ionized metal lines begin to appear.

Procyon A (F5IV–V) is a nearby example with a temperature near 6,500 K and luminosity about 7 L☉. F stars have stable photospheres and lifetimes of several billion years, which makes them attractive for exoplanet characterization and asteroseismology studies.

5. G-type stars — Yellow suns like our Sun

G-type stars include the Sun (G2V). Surface temperatures typically range from about 5,200 to 6,000 K and masses are roughly 0.8–1.04 M☉.

G-type main-sequence lifespans are about 10 billion years; the Sun is roughly 4.6 billion years into its ~10 billion-year main-sequence life. Among the types of stars, G-types strike a balance of stable energy output and long-term habitability, which is why they dominate much of the discussion about Earth-like worlds.

NASA’s solar observations provide the best-studied template for a G star, and many Kepler and TESS hosts fall into this class, giving a large sample for comparative planetology.

Cool and Low-mass Stars

The cool end of the sequence contains K- and M-type stars, which make up the bulk of the Milky Way’s stellar population. M dwarfs alone account for roughly 70–75% of stars in the Galaxy, so they dominate by number.

These stars have lower temperatures and luminosities, spectra rich in molecular bands (TiO is prominent in M stars), and incredibly long lifespans. Some M dwarfs can theoretically outlive the current age of the universe by many orders of magnitude.

K and M stars are central to exoplanet searches because their small sizes boost transit and radial-velocity signals from Earth-size planets. For population statistics and stellar census data, the ESA Gaia results and NASA surveys are excellent references.

6. K-type stars — Orange, stable, and long-lived

K-type stars have surface temperatures roughly 3,700–5,200 K. Main-sequence K dwarfs typically carry between about 0.45 and 0.8 M☉ and shine with orange tones.

Giants like Arcturus are evolved K stars, but main-sequence K dwarfs are long-lived — lasting several to tens of billions of years depending on mass. Their habitable zones are wider than for M dwarfs and their activity levels are often lower than those of red dwarfs, making them promising targets for habitable-planet searches. An example exoplanet host is HD 40307 (K2.5V).

7. M-type stars — Red dwarfs, abundant and long-lived

M dwarfs have surface temperatures below about 3,700 K and masses under roughly 0.45 M☉. They’re small, faint, and incredibly common — they make up the majority of stars in our neighborhood and the Galaxy at large.

Their theoretical lifespans stretch from tens of billions to trillions of years because they burn fuel so slowly. Nearby examples with high public interest include Proxima Centauri (M5.5Ve), the Sun’s nearest stellar neighbor, and TRAPPIST-1 (M8V), known for its seven small planets.

M dwarfs are magnetically active at times and can flare, which complicates habitability for close-in planets. Still, their abundance and the ease of detecting small planets around them make M stars central to ongoing exoplanet discovery programs (see the NASA Exoplanet Archive).

Summary

• The seven spectral types in order are O → B → A → F → G → K → M, a sequence that tracks decreasing temperature and increasing lifespan.
• As you move from hot to cool: temperatures, masses, and luminosities fall while main-sequence lifetimes rise from millions (O) to trillions of years (low-mass M dwarfs).
• Different classes matter for different reasons — massive O and B stars drive nucleosynthesis and galactic ecology, A–G stars are prime targets for detailed stellar physics and planet searches, and K/M stars dominate exoplanet yield and long-term habitability studies.
• Quick reminders: the Sun is a G2V star (about 4.6 billion years old), spot bright stars like Rigel and Vega with binoculars, and use NASA or ESA pages (and the NASA Exoplanet Archive) for up-to-date data.
• If you want to learn more, observe with a small telescope or app, follow NASA/ESA mission pages, and check recent Gaia results for stellar census statistics.