Just-saturated RGB-camera discs
Alpha Centauri is the brightest object in the constellation of Centaurus (top left).
Main-sequence stars arranged from O to M Harvard classes
Apparent and true orbits of Alpha Centauri. The A component is held stationary, and the relative orbital motion of the B component is shown. The apparent orbit (thin ellipse) is the shape of the orbit as seen by an observer on Earth. The true orbit is the shape of the orbit viewed perpendicular to the plane of the orbital motion. According to the radial velocity versus time, the radial separation of A and B along the line of sight had reached a maximum in 2007, with B being further from Earth than A. The orbit is divided here into 80 points: each step refers to a timestep of approx. 0.99888 years or 364.84 days.
The Hertzsprung–Russell diagram relates stellar classification with absolute magnitude, luminosity, and surface temperature.
The relative sizes and colours of stars in the Alpha Centauri system, compared to the Sun
Montage of false color spectra for main-sequence stars
Relative positions of Sun, Alpha Centauri AB and Proxima Centauri. Grey dot is projection of Proxima Centauri, located at the same distance as Alpha Centauri AB.
Guide for Secchi spectral types ("152 Schjellerup" is Y Canum Venaticorum)
The two bright stars at the lower right are Alpha (right) and Beta Centauri (left, above antenna). A line drawn through them points to the four bright stars of the Southern Cross, just to the right of the dome of the Danish 1.54 m telescope at La Silla Observatory in Chile.
Proper motion of stars of early type in ± 200,000 years
Alpha Centauri AB taken in daylight by holding a Canon Powershot S100 in line with the eyepiece of a 110-mm refractor. The photo is one of the best frames of a video. The double star is clearly visible.
The movement of stars of late type around the apex (left) and antapex (right) in ± 200,000 years
View of Alpha Centauri from the Digitized Sky Survey-2
The spectrum of an O5V star
Alpha Centauri A is of the same stellar type G2 as the Sun, while Alpha Centauri B is a K1-type star.
B-class stars in the Jewel Box cluster (Credit: ESO VLT)
Closest stars to the Sun
Class A Vega (left) compared to the Sun (right)
Distances of the nearest stars from 20,000 years ago until 80,000 years in the future
Canopus, an F-type supergiant and the second-brightest star in the night sky
Animation showing motion of Alpha Centauri through the sky. (The other stars are held fixed for didactic reasons) "Oggi" means today. "Anni" means years.
The Sun, a G2 main-sequence star, with dark sunspots
The discovery image of Alpha Centauri's candidate Neptunian planet, marked here as "C1".
Arcturus, a K1.5 giant compared to the Sun and Antares
Looking towards the sky around Orion from Alpha Centauri with Sirius near Betelgeuse, Procyon in Gemini, and the Sun in Cassiopeia generated by Celestia.
UGC 5797, an emission-line galaxy where massive bright blue stars are formed
Simulated night-sky image with a "W" of stars from Cassiopeia connected by lines, and the Sun, labeled "Sol", as it would appear to the left of the "W"
Hubble Space Telescope image of the nebula M1-67 and the Wolf–Rayet star WR 124 in the center
The Very Large Telescope and Alpha Centauri
Artist's impression of an L-dwarf
Artist's impression of a T-dwarf
Artist's impression of a Y-dwarf
Image of the carbon star R Sculptoris and its striking spiral structure
Sirius A and B (a white dwarf of type DA2) resolved by Hubble

Alpha Centauri C, or Proxima Centauri, is a small faint red dwarf (Class M).

- Alpha Centauri

There are also giant K-type stars, which range from hypergiants like RW Cephei, to giants and supergiants, such as Arcturus, whereas orange dwarfs, like Alpha Centauri B, are main-sequence stars.

- Stellar classification
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5 related topics with Alpha

Overall

Hubble Space Telescope image of Sirius A and Sirius B. The white dwarf can be seen to the lower left. The diffraction spikes and concentric rings are instrumental effects.

Sirius

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Brightest star in the night sky.

Brightest star in the night sky.

Hubble Space Telescope image of Sirius A and Sirius B. The white dwarf can be seen to the lower left. The diffraction spikes and concentric rings are instrumental effects.
Sirius (bottom) and the constellation Orion (right). The three brightest stars in this image—Sirius, Betelgeuse (top right) and Procyon (top left)—form the Winter Triangle. The bright star at top center is Alhena, which forms a cross-shaped asterism with the Winter Triangle.
The orbit of Sirius B around A as seen from Earth (slanted ellipse). The wide horizontal ellipse shows the true shape of the orbit (with an arbitrary orientation) as it would appear if viewed straight on.
A Chandra X-ray Observatory image of the Sirius star system, where the spike-like pattern is due to the support structure for the transmission grating. The bright source is Sirius B. Credit: NASA/SAO/CXC
Comparison of Sirius A and the Sun, to scale and relative surface brightness
Size comparison of Sirius B and Earth
A bust of Sopdet, Egyptian goddess of Sirius and the fertility of the Nile, syncretized with Isis and Demeter
Sirius midnight culmination at New Year 2022 local solar time
Yoonir, symbol of the universe in Serer religion

Sirius is a binary star consisting of a main-sequence star of spectral type A0 or A1, termed Sirius A, and a faint white dwarf companion of spectral type DA2, termed Sirius B. The distance between the two varies between 8.2 and 31.5 astronomical units as they orbit every 50 years.

This proximity is the main reason for its brightness, as with other near stars such as Alpha Centauri, Procyon and Vega and in contrast to distant, highly luminous supergiants such as Canopus, Rigel or Betelgeuse.(Note that Canopus may be a bright giant) It is still around 25 times more luminous than the Sun.

61 Cygni, a binary K-type star system.

K-type main-sequence star

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61 Cygni, a binary K-type star system.

A K-type main-sequence star, also referred to as a K-type dwarf or an orange dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars ("red dwarfs") and yellow/white G-type main-sequence stars.

Well-known examples include Alpha Centauri B (K1 V) and Epsilon Indi (K5 V).

Arcturus is the brightest star in the constellation of Boötes.

Arcturus

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Brightest star in the northern constellation of Boötes, the fourth-brightest in the night sky, and the brightest in the northern celestial hemisphere.

Brightest star in the northern constellation of Boötes, the fourth-brightest in the night sky, and the brightest in the northern celestial hemisphere.

Arcturus is the brightest star in the constellation of Boötes.
Optical image of Arcturus (DSS2 / MAST / STScI / NASA)
Arcturus in Arctophyllax
Arcturus next to the head of Comet Donati in 1858

Located relatively close at 36.7 light-years from the Sun, Arcturus is a single red giant of spectral type K1.5III—an aging star around 7.1 billion years old that has used up its core hydrogen and evolved off the main sequence.

With an apparent visual magnitude of −0.05, Arcturus is the brightest star in the northern celestial hemisphere and the fourth-brightest star in the night sky, after Sirius (−1.46 apparent magnitude), Canopus (−0.72) and α Centauri (combined magnitude of −0.27).

61 Cygni showing proper motion (movement from our vantage point) at some early 21st century one-year intervals.

61 Cygni

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Binary star system in the constellation Cygnus, consisting of a pair of K-type dwarf stars that orbit each other in a period of about 659 years.

Binary star system in the constellation Cygnus, consisting of a pair of K-type dwarf stars that orbit each other in a period of about 659 years.

61 Cygni showing proper motion (movement from our vantage point) at some early 21st century one-year intervals.
A size comparison between the Sun (left), 61 Cygni A (bottom) and 61 Cygni B (upper right).
The orbital motion of component B relative to component A as seen from Earth as well as the true appearance from face-on view. The time steps are approximately 10 years.

His measurement was published only shortly before similar parallax measurements of Vega by Friedrich Georg Wilhelm von Struve and Alpha Centauri by Thomas Henderson that same year.

Although it appears to be a single star to the naked eye, 61 Cygni is a widely-separated binary star system, composed of two K class (orange) main sequence stars, the brighter 61 Cygni A and fainter 61 Cygni B, which have apparent magnitudes of 5.2 and 6.1, respectively.

The smaller object is Gliese 229B, about 20 to 50 times the mass of Jupiter, orbiting the star Gliese 229. It is in the constellation Lepus, about 19 light-years from Earth.

Brown dwarf

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Brown dwarfs are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen (1H) into helium in their cores, unlike a main-sequence star.

Brown dwarfs are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen (1H) into helium in their cores, unlike a main-sequence star.

The smaller object is Gliese 229B, about 20 to 50 times the mass of Jupiter, orbiting the star Gliese 229. It is in the constellation Lepus, about 19 light-years from Earth.
Planets, brown dwarfs, stars (not to scale)
An artistic concept of the brown dwarf around the star HD 29587, a companion known as HD 29587 b, and estimated to be about 55 Jupiter masses
A size comparison between the Sun, a young sub-brown dwarf, and Jupiter. As the sub-brown dwarf ages, it will gradually cool and shrink.
Artist's vision of a late-M dwarf
Artist's vision of an L dwarf
Artist's vision of a T dwarf
Artist's vision of a Y dwarf
WISE 0458+6434 is the first ultra-cool brown dwarf (green dot) discovered by WISE. The green and blue comes from infrared wavelengths mapped to visible colors.
Artist's illustration of a brown dwarf's interior structure. Cloud layers at certain depths are offset as a result of layer shifting.
Wind measured (Spitzer ST; Artist Concept; 9 Apr 2020)
Brown dwarfs Teide 1, Gliese 229B, and WISE 1828+2650 compared to red dwarf Gliese 229A, Jupiter and our Sun
Chandra image of LP 944-20 before flare and during flare
Multi-epoch images of brown dwarf binaries taken with the Hubble Space Telescope. The binary Luhman 16 AB (left) is closer to the Solar System than the other examples shown here.
A visualization representing a three-dimensional map of brown dwarfs (red dots) that have been discovered within 65 light-years of the Sun
The HH 1165 jet launched by the brown dwarf Mayrit 1701117 in the outer periphery of the sigma Orionis cluster
Artist's impression of a disc of dust and gas around a brown dwarf
Brown dwarf illustration<ref>{{cite web |first1=Megan |last1=Tannock |first2=Stanimir |last2=Metchev |first3=Amanda |last3=Kocz |title=Caught Speeding: Clocking the Fastest-Spinning Brown Dwarfs |url=https://noirlab.edu/public/news/noirlab2114/ |publisher=NOIRLab |date=7 April 2021 |access-date=9 April 2021 }}</ref>

Astronomers classify self-luminous objects by spectral class, a distinction intimately tied to the surface temperature, and brown dwarfs occupy types M, L, T, and Y. As brown dwarfs do not undergo stable hydrogen fusion, they cool down over time, progressively passing through later spectral types as they age.

Luhman 16 is the third closest system to the Sun after Alpha Centauri and Barnard's Star.