page_title: Betelgeuse
section_title: Observation
hierarchical_section_title: Betelgeuse / Observation
caption_attribution_description: English: Photo taken by Rogelio Bernal Andreo in October 2010 of the Orion constellation showing the surrounding nebulas of the Orion Molecular Cloud complex. Also captured is the red supergiant Betelgeuse (top left) and the famous belt of Orion composed of the OB stars Altitak, Alnilam and Mintaka. To the bottom right can be found the star Rigel. The red crescent shape is Barnard's Loop. The photograph appeared as the Astronomy Picture of the Day on October 23, 2010.
context_page_description: Betelgeuse is usually the tenth-brightest star in the night sky and, after Rigel, the second-brightest in the constellation of Orion. It is a distinctly reddish semiregular variable star whose apparent magnitude, varying between +0.0 and +1.6, has the widest range displayed by any first-magnitude star. At near-infrared wavelengths, Betelgeuse is the brightest star in the night sky. Its Bayer designation is α Orionis, Latinised to Alpha Orionis and abbreviated Alpha Ori or α Ori.
  Classified as a red supergiant of spectral type M1-2, Betelgeuse is one of the largest stars visible to the naked eye. If it was at the center of our Solar System, its surface would lie beyond the asteroid belt and it would engulf the orbits of Mercury, Venus, Earth, Mars, and possibly Jupiter. Nevertheless, there are several larger red supergiants in the Milky Way, including VY Canis Majoris and possibly Mu Cephei. Calculations of Betelgeuse’s mass range from slightly under ten to a little over twenty times that of the Sun. It is calculated to be about 700 light-years from the Sun, indicating an absolute magnitude of about −6.
context_section_description: As a result of its distinctive orange-red color and position within Orion, Betelgeuse is easy to spot with the naked eye in the night sky. It is one of three stars that make up the Winter Triangle asterism, and it marks the center of the Winter Hexagon. At the beginning of January of each year, it can be seen rising in the east just after sunset. Between mid-September to mid-March (best in mid-December), it is visible to virtually every inhabited region of the globe, except in Antarctica at latitudes south of 82°. In May (moderate northern latitudes) or June (southern latitudes), the red supergiant can be seen briefly on the western horizon after sunset, reappearing again a few months later on the eastern horizon before sunrise. In the intermediate period (June–July), it is invisible to the naked eye (visible only with a telescope in daylight), except around midday in Antarctic regions between 70° and 80° south latitude (during polar night, when the Sun is below the horizon).
  Betelgeuse is a variable star whose visual magnitude ranges between 0.0 and +1.6. There are periods when it will surpass Rigel to become the sixth brightest star, and occasionally it will be even brighter than Capella. At its faintest Betelgeuse can fall behind Deneb and Beta Crucis, themselves both slightly variable, to be the twentieth-brightest star.
  Betelgeuse has a B–V color index of 1.85—a figure which points to its pronounced "redness". The photosphere has an extended atmosphere, which displays strong lines of emission rather than absorption, a phenomenon that occurs when a star is surrounded by a thick gaseous envelope (rather than ionized). This extended gaseous atmosphere has been observed moving toward and away from Betelgeuse, depending on fluctuations in the photosphere. Betelgeuse is the brightest near-infrared source in the sky with a J band magnitude of −2.99; only about 13% of the star's radiant energy is emitted as visible light. If human eyes were sensitive to radiation at all wavelengths, Betelgeuse would appear as the brightest star in the night sky.
  Various catalogues list up to nine faint visual companions to Betelgeuse. They are at distances of about one to four arc-minutes and all are fainter than 10th magnitude.
  In December 2019, astronomers reported that the star's brightness had significantly decreased and that it may therefore be in the last stages of its evolution. Studies reported more recently, on 22 February 2020, suggest that Betelgeuse may have stopped dimming, and may now be beginning to again brighten, all but ending the current dimming episode. Further studies of the star, reported on 24 February 2020, found no significant change in the infrared over the last 50 years, and seems unrelated to the recent visual fading, suggesting that an impending core collapse may be unlikely. Also, on 24 February 2020, further studies suggest that occluding "large-grain circumstellar dust" may be the most likely explanation for the dimming of the star. On 26 February 2020, astronomers reported large amounts of Titanium(II) oxide (TiO), one of the star's dust precursors, in spectral studies, suggesting that the star may be cooling.
caption: Image showing Betelgeuse (top left) and the dense nebulae of the Orion Molecular Cloud Complex (Rogelio Bernal Andreo)
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