Betelgeuse

α OriBetelg'''euseBetelgeuse mass lossBetelgeusiansee belowα Ori (Betelgeuse)
Betelgeuse, also designated α Orionis (Latinised to Alpha Orionis, abbreviated Alpha Ori, α Ori), is on average the ninth-brightest star in the night sky and second-brightest in the constellation of Orion.wikipedia
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Orion (constellation)

Orionconstellation of OrionOrion constellation
Betelgeuse, also designated α Orionis (Latinised to Alpha Orionis, abbreviated Alpha Ori, α Ori), is on average the ninth-brightest star in the night sky and second-brightest in the constellation of Orion.
Its brightest stars are Rigel (Beta Orionis) and Betelgeuse (Alpha Orionis), a blue-white and a red supergiant, respectively.

List of brightest stars

brightest starsbrightest starone of the brightest stars
Betelgeuse, also designated α Orionis (Latinised to Alpha Orionis, abbreviated Alpha Ori, α Ori), is on average the ninth-brightest star in the night sky and second-brightest in the constellation of Orion.
New or more accurate photometry, standard filters, or adopting differing methods using standard stars can measure stellar magnitudes slightly differently. This may change the apparent order of lists of bright stars. The table shows measured V magnitudes, which use a specific filter that closely approximates human vision. However, other kinds of magnitude systems do exist based on different wavelengths, some well away from the distribution of the visible wavelengths of light, and these apparent magnitudes vary dramatically in the different systems. For example, Betelgeuse has the K-band (infra-red) apparent magnitude of −4.05.

Winter Triangle

Betelgeuse is one of three stars that make up the Winter Triangle asterism, and it marks the center of the Winter Hexagon.
It is an imaginary equilateral triangle drawn on the celestial sphere, with its defining vertices at Sirius, Betelgeuse, and Procyon, the primary stars in the three constellations of Canis Major, Orion, and Canis Minor, respectively.

Rigel

β Ori (Rigel)B2 IaeBeta Orionis
From 1836 to 1840, he noticed significant changes in magnitude when Betelgeuse outshone Rigel in October 1837 and again in November 1839.
Rigel, also designated β Orionis (Latinized to Beta Orionis, abbreviated Beta Ori, β Ori), is on average the seventh-brightest star in the night sky and the brightest in the constellation of Orion—though occasionally it is outshone within the constellation by the variable star Betelgeuse.

Apparent magnitude

apparent visual magnitudemagnitudevisual magnitude
It is distinctly reddish, and is a semiregular variable star whose apparent magnitude varies between 0.0 and 1.3, the widest range of any first-magnitude star.
On early 20th century and older orthochromatic (blue-sensitive) photographic film, the relative brightnesses of the blue supergiant Rigel and the red supergiant Betelgeuse irregular variable star (at maximum) are reversed compared to what human eyes perceive, because this archaic film is more sensitive to blue light than it is to red light.

Absolute magnitude

Hbolometric magnitudeabsolute magnitude (H)
It is calculated to be 640 light-years away, yielding an absolute magnitude of about −6. Less than 10 million years old, Betelgeuse has evolved rapidly because of its high mass. Having been ejected from its birthplace in the Orion OB1 Association—which includes the stars in Orion's Belt—this runaway star has been observed moving through the interstellar medium at a speed of 30 km/s, creating a bow shock over four light-years wide.
Examples include Rigel (−7.0), Deneb (−7.2), Naos (−6.0), and Betelgeuse (−5.6).

Asterism (astronomy)

asterismasterismsconstellation
Betelgeuse is one of three stars that make up the Winter Triangle asterism, and it marks the center of the Winter Hexagon.
One-third of the 1st-magnitude stars visible in the sky (seven of twenty-one) are in the so-called Winter Hexagon with Capella, Aldebaran, Rigel, Sirius, Procyon, and Pollux with 2nd-magnitude Castor, on the periphery, and Betelgeuse off-center. Although somewhat flattened, and thus more elliptical than circular, the figure is so large that it cannot be taken in all at once, thus making the lack of true circularity less noticeable. (The projection in the chart exaggerates the stretching.) Some prefer to regard it as a Heavenly 'G'.

Bayer designation

Bayerdesignationdesignations
α Orionis (Latinised to Alpha Orionis) is the star's Bayer designation.

List of largest stars

largest known starslargest stars knownlargest stars
Classified as a red supergiant of spectral type M1-2, the star is one of the largest stars visible to the naked eye.

Winter Hexagon

Winter Circle
Betelgeuse is one of three stars that make up the Winter Triangle asterism, and it marks the center of the Winter Hexagon.
The third vertex is Betelgeuse, which lies near the center of the hexagon.

Mu Cephei

μ Cepμ CepheiGarnet Star
However, there are several other red supergiants in the Milky Way that could be larger, such as Mu Cephei and VY Canis Majoris.
A determination of the distance based upon a size comparison with Betelgeuse gives an estimate of 390 ± 140 parsecs, so it is clear that Mu Cephei is either a much larger star than Betelgeuse or much closer (and smaller and less luminous) than expected.

Semiregular variable star

semiregularsemi-regular variablesemiregular variable
It is distinctly reddish, and is a semiregular variable star whose apparent magnitude varies between 0.0 and 1.3, the widest range of any first-magnitude star.
Catalogued SRc stars are less numerous, but include some of the brightest stars in the sky such as Betelgeuse and α Her.

Astronomical spectroscopy

spectrumspectroscopicspectra
Lines in the spectrum of Betelgeuse show doppler shifts indicating radial velocity changes corresponding, very roughly, to the brightness changes.
Soon after this, he combined telescope and prism to observe the spectrum of Venus, the Moon, Mars, and various stars such as Betelgeuse; his company continued to manufacture and sell high-quality refracting telescopes based on his original designs until its closure in 1884.

Francis G. Pease

F. G. PeaseFrancis Pease
In 1920, Albert Michelson and Francis Pease mounted a 6-meter interferometer on the front of the 2.5-meter telescope at Mount Wilson Observatory.
In 1920, Michelson and Pease were able to use the Michelson stellar interferometer fitted to the 100 in telescope at Mt. Wilson to measure the angular diameter of the star Betelgeuse.

Mount Wilson Observatory

Mount WilsonMt. WilsonHooker Telescope
In 1920, Albert Michelson and Francis Pease mounted a 6-meter interferometer on the front of the 2.5-meter telescope at Mount Wilson Observatory.
Michelson was able to use the equipment to determine the precise diameter of stars, such as Betelgeuse, the first time the size of a star had ever been measured.

Albert A. Michelson

MichelsonAlbert MichelsonA. A. Michelson
In 1920, Albert Michelson and Francis Pease mounted a 6-meter interferometer on the front of the 2.5-meter telescope at Mount Wilson Observatory.
Michelson had invented astronomical interferometry and built such an instrument at the Mount Wilson Observatory which was used to measure the diameter of the red giant Betelgeuse.

VY Canis Majoris

VY CMa
However, there are several other red supergiants in the Milky Way that could be larger, such as Mu Cephei and VY Canis Majoris.
In 2009, Nathan Smith of the University of California, Ken Hinkle and Nils Ride of the Lund Observatory have used the PHOENIX near-infrared spectrograph on Gemini South to study the geometry and kinematics of the active circumstellar envelopes of two large supergiant stars: Betelgeuse and VY Canis Majoris.

J band (infrared)

J bandJJ-band
Betelgeuse is the brightest near-infrared source in the sky with a J band magnitude of −2.99.
Betelgeuse is the brightest near-IR source in the sky with a J band magnitude of −2.99.

R Doradus

R Dor
The angular diameter of Betelgeuse is only exceeded by R Doradus and the Sun.
With a near-infrared J band magnitude of −2.6, only Betelgeuse at −2.9 is brighter.

Red supergiant star

red supergiantred supergiantsred
Classified as a red supergiant of spectral type M1-2, the star is one of the largest stars visible to the naked eye.
Betelgeuse and Antares are the brightest and best known red supergiants (RSGs), indeed the only first magnitude red supergiant stars.

Supernova

supernovaecore-collapse supernovasupernovas
Currently in a late stage of stellar evolution, the supergiant is expected to explode as a supernova within the next million years.
A number of close or well known stars have been identified as possible core collapse supernova candidates: the red supergiants Antares and Betelgeuse; the yellow hypergiant Rho Cassiopeiae; the luminous blue variable Eta Carinae that has already produced a supernova impostor; and the brightest component, a Wolf–Rayet star, in the Regor or Gamma Velorum system, Others have gained notoriety as possible, although not very likely, progenitors for a gamma-ray burst; for example WR 104.

Luminosity

luminousbolometric luminosityluminosities
It is distinctly reddish, and is a semiregular variable star whose apparent magnitude varies between 0.0 and 1.3, the widest range of any first-magnitude star. Knowledge of the star's distance improves the accuracy of other stellar parameters, such as luminosity that, when combined with an angular diameter, can be used to calculate the physical radius and effective temperature; luminosity and isotopic abundances can also be used to estimate the stellar age and mass.
Certain stars like Deneb and Betelgeuse are found above and to the right of the main sequence, more luminous or cooler than their equivalents on the main sequence.

Effective temperature

surface temperatureeffective (surface) temperaturetemperature
Knowledge of the star's distance improves the accuracy of other stellar parameters, such as luminosity that, when combined with an angular diameter, can be used to calculate the physical radius and effective temperature; luminosity and isotopic abundances can also be used to estimate the stellar age and mass.
A red star could be a tiny red dwarf, a star of feeble energy production and a small surface or a bloated giant or even supergiant star such as Antares or Betelgeuse, either of which generates far greater energy but passes it through a surface so large that the star radiates little per unit of surface area.

Martin Schwarzschild

The 1950s and 1960s saw two developments that would affect stellar convection theory in red supergiants: the Stratoscope projects and the 1958 publication of Structure and Evolution of the Stars, principally the work of Martin Schwarzschild and his colleague at Princeton University, Richard Härm.
Betelgeuse

Stellar mass loss

mass lossejected
It is also surrounded by a complex, asymmetric envelope roughly 250 times the size of the star, caused by mass loss from the star itself.
Betelgeuse