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.

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.

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.

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.

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.

Bayer designation

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

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.

Procyon

Canis minorProcyon Aα CMi
Procyon is usually the eighth-brightest star in the night sky, culminating at midnight on January 14. It forms one of the three vertices of the Winter Triangle asterism, in combination with Sirius and Betelgeuse.

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.

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.

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).

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.

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.

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.

The Hitchhiker's Guide to the Galaxy

Hitchhiker's Guide to the GalaxyHitchhiker's GuideHitchhiker
In the popular science fiction series The Hitchhiker's Guide to the Galaxy by Douglas Adams, Ford Prefect was from "a small planet somewhere in the vicinity of Betelgeuse."
Dent's adventures intersect with several other characters: Ford Prefect (who named himself after the Ford Prefect car to blend in with what was assumed to be the dominant life form, automobiles), an alien from a small planet somewhere in the vicinity of Betelgeuse and a researcher for the eponymous guidebook, who rescues Dent from Earth's destruction; Zaphod Beeblebrox, Ford's eccentric semi-cousin and the Galactic President; the depressed robot Marvin the Paranoid Android; and Trillian, formerly known as Tricia McMillan, a woman Arthur once met at a party in Islington and the only other human survivor of Earth's destruction thanks to Beeblebrox' intervention.

Very Large Telescope

VLTNACOVLTI
In July 2009, images released by the European Southern Observatory, taken by the ground-based Very Large Telescope Interferometer (VLTI), showed a vast plume of gas extending 30 AU from the star into the surrounding atmosphere.
The interferometry (combining light from multiple telescopes) is used about 20 percent of the time for very high-resolution on bright objects, for example, on Betelgeuse.

Stellar classification

spectral typeK-typeG-type
Classified as a red supergiant of spectral type M1-2, the star is one of the largest stars visible to the naked eye.
Although most class M stars are red dwarfs, most of the largest ever supergiant stars in the Milky Way are M stars, such as VY Canis Majoris, Antares and Betelgeuse, which are also class M. Furthermore, the larger, hotter brown dwarfs are late class M, usually in the range of M6.5 to M9.5.

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.

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.

First magnitude star

brightestfirst magnitudefirst magnitude stars

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.

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.

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.

Magnitude (astronomy)

magnitudemagnitudesmag
Betelgeuse is the brightest near-infrared source in the sky with a J band magnitude of −2.99.
Betelgeuse (apparent magnitude 0.5, absolute magnitude −5.8) appears slightly dimmer in the sky than Alpha Centauri (apparent magnitude 0.0, absolute magnitude 4.4) even though it emits thousands of times more light, because Betelgeuse is much farther away.