This video is Betelgeuse in the constellation of Orion. Betelgeuse, also known by its Bayer designation Alpha Orionis, α Orionis or α Ori, is the ninth-brightest star in the night sky and second-brightest in the constellation of Orion. Distinctly reddish, it is a semiregular variable star whose apparent magnitude varies between 0.2 and 1.2, the widest range of any first-magnitude star. Betelgeuse is one of three stars that make up the Winter Triangle, and it marks the center of the Winter Hexagon. The stars name is derived from the Arabic يد الجوزاء Yad al-Jauzā, meaning the hand of Orion. The Arabic character for Y has been misread as B by medieval translators, giving cause to the initial B in Betelgeuse. The star is classified as a red supergiant of spectral type M2Iab and is one of the largest and most luminous observable stars. If Betelgeuse were at the center of the Solar System, its surface would extend past the asteroid belt, possibly to the orbit of Jupiter and beyond, wholly engulfing Mercury, Venus, Earth and Mars. Estimates of its mass are poorly constrained, but range from 5 to 30 times that of the sun. Its distance from Earth was estimated in 2008 at 640 light-years, yielding a mean absolute magnitude of about −6.02. 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 Orions Belt, this crimson runaway has been observed moving through the interstellar medium at a supersonic speed of 30 km/s, creating a bow shock over 4 light-years wide. Currently in a late stage of stellar evolution, the supergiant is expected to proceed through its life cycle before exploding as a type II supernova within the next million years. An observation by the Herschel Space Observatory in January 2013 revealed that the stars winds are crashing against the surrounding interstellar medium. In 1920, Betelgeuse became the second star after the Sun to have the angular size of its photosphere measured. Since then, researchers have used telescopes with different technical parameters to measure the stellar giant, often with conflicting results. Studies since 1990 have produced an angular diameter, apparent size, ranging from 0.043 to 0.056 arcseconds, an incongruity largely caused by the stars tendency to periodically change shape. Due to limb darkening, variability, and angular diameters that vary with wavelength, many of the stars properties are not yet known with any certainty. Adding to these challenges, the surface of Betelgeuse is obscured by a complex, asymmetric envelope roughly 250 times the size of the star, caused by colossal mass loss. The measured parallax of Betelgeuse was π = 7.63 ± 1.64 mas, which equated to a distance of 131 pc or roughly 430 ly, and had a smaller reported error than previous measurements. However, later evaluation of the Hipparcos parallax measurements for variable stars like Betelgeuse found that the uncertainty of these measurements had been underestimated. In 2007, Floor van Leeuwen improved upon the Hipparcos parallax, producing a new figure of π = 6.55 ± 0.83, hence a much tighter error factor yielding a distance of roughly 152 ± 20 pc or 520 ± 73 ly. In 2008, Graham Harper and colleagues, using VLA: the Very Large Array, produced a radio solution of π = 5.07 ± 1.10 mas, equaling a distance of 197 ± 45 pc or 643 ± 146 ly. As Harper points out: The revised Hipparcos parallax leads to a larger distance (152 ± 20 pc) than the original; however, the astrometric solution still requires a significant cosmic noise of 2.4 mas. Given these results it is clear that the Hipparcos data still contain systematic errors of unknown origin. Although the radio data also have systematic errors, the Harper solution combines the datasets in the hope of mitigating such errors. ESA: The European Space Agencys upcoming Gaia mission may not improve over the measurements of Betelgeuse by the earlier Hipparcos mission because it is brighter than the approximately V=6 saturation limit of the missions instruments. Hisashi UMEKUBO/Senior Space Mission Controller/ESA/JAXA/Master of Engineering/First-class radio operator for general services, First-Class Technical Radio Operator for On-the-Ground Services :-)
Posted on: Sat, 05 Jul 2014 04:48:41 +0000
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