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On December 13, 1920, Albert Abraham Michaelson and Francis Pease measured diameter of the star Betelgeuse, the first measurement of the size of any star other than the Sun. Although the relative size of Betelgeuse has been in dispute since then mostly due to its massive size and incredible speed through space, the methods devised by Michaelson and Pease have been used for decades. The name Betelgeuse is derived from the Arabic يد الجوزاء (Yad al-Jauzā’), meaning the Hand of al-Jauzāal-Jauzā being the constellation known in the west as Orion the Hunter. Betelgeuse is the right shoulder (or armpit) of Orion and the alpha star of the constellation.  The letter B in Betelgeuse, however, was a mistransliteration from Arabic into medieval Latin of the first character Y, which was misread as a B. Betelgeuse arrived in English in 1515 as a direct phonetic transliteration of the Arabic as Ibt al Jauzah, which due to this mispelling was also mistranslated as the Armpit of the Central One. Intermediary forms include Bed Elgueze, Beit Algueze, Betelgeux and Betelgeuze, finally settling on Betelgeuse around the time Michaelson and Pease were measuring the star.

Everything about this star has been misunderstood for centuries, starting with its name in English and continuing to the present day. When Michaelson and Pease attempted to measure its size, interferometry was still a new science and early estimates both missed its size and proximity. Long considered the largest star in the catalog (currently Betelgeuse ranks third largest), Betelgeuse is a massive red super giant millions of times larger than the sun.  As recently as the last ten or fifteen years the size and distance of Betelgeuse have been refined and updated as new and improved methods have been implemented.  

Michaelson, the scientist who first measured Betelgeuse, had a life scripted by Hollywood: his parents fled Poland when he was only two years old and settled in the American West. Michaelson recieved an appointment from no less than President Ulysses S. Grant to attend the fledgling United States Naval Academy in Annapolis, Maryland where he began his scientific endeavors in earnest. He is actually more famous for his experiments to measure the speed of light accurately, known as the Michaelson-Morley experiment, which he began while in Annapolis and which he continued to refine for decades as he tried to measure the impact of aether on the speed of light.  He never was able to find evidence of aether, which later became significant and celebrated when Einstein published his Special Theory of Relativity. He was awarded most major scientific prizes including the Nobel Prize of 1907 and is considered the first American to win that prize. His life was so dramatic and crammed with acheivement that his early life and appointment to USNA managed to penetrate into popular culture when his life was celebrated on an episode of Gunsmoke, in which an unpleasant local teacher attempts to block his advancement.  The episode Look to the Stars was broadcast in March 1962, 31 years after his death on May 9, 1931.  

Although Michaelson and Pease’s first measurement has been in flux since publication, this was not due to flaws in their science or methodology.  As recently as 1991 the Yale University Observatory measured the distance to Betelgeuse at 330 light years.  The Hipparcos Input Catalog measured the distance two years later at 650 light years, almost doubling Yale’s measurement.  In 2008 a team working with Very Large Array Radio Telescopes lead by Graham Harper measured the distance at 643 light years with a margin of error of plus or minus 146 (!!!) light years.  

Thursday, February 16, 2012

A Messier Object is an astronomical object first described by the great French astronomer Charles Messier in 1771. An insatiable comet hunter, Messier began his catalog of objects that were neither stars nor comets as a way of accounting for them and subsequently avoiding them as he searched for comets. With the help of his assistant Pierre Méchain, the first edition of the Catalogue des Nébuleuses et des Amas d’Étoiles (Catalogue of Nebulae and Star Clusters) contained 45 objects, mostly nebulae, galaxies and star clusters. According to Messier, who was waiting for the return of Halley’s Comet:

What caused me to undertake the catalog was the nebula I discovered above the southern horn of Taurus on September 12, 1758, whilst observing the comet of that year. This nebula had such a resemblance to a comet in its form and brightness that I endeavored to find others, so that astronomers would no more confuse these same nebulae with comets just beginning to appear.

Messier’s final publication included 103 objects, but the catalog was added to as recently as 1966, almost 200 years after his original publication! Today the catalog contains 110 objects and many objects are still referred to by their Messier number.

All images in the public domain, courtesy NASA.