60 years of observations of the interstellar magnetic field


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60 years of observations of the interstellar magnetic field
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1948 was an important year....

Chandra had predicted that continuum emission from non-spherical stars should be polarized.  In 1946 William Hiltner used the Yerkes 40" to observe a close binary star system during eclipse. The hot star was a Be star and so expected to be non-spherical, and the late type star that eclipsed it should have been spherical. He looked for polarization changes during the eclipse of the hot star. Hiltner said that he thought he saw something but was not sure. This was done photographically(!!).  He outlined ways of improving the measurements.

The very first observations of the galactic magnetic field were made in 1948, independently by William Hiltner of Yerkes Observatory and by John Hall of Amherst College and the U. S. Naval Observatory.  Both observed polarization of starlight, and both published their results in Science in 1949.  Later that same year, Davis & Greenstein published a letter in the Physical Review explaining the effect as a result of magnetically aligned interstellar grains.  Hiltner and Hall originally intended to collaborate on these observations in the summer of 1948, using the McDonald Observatory 82" telescope.  However, Hall was unable to be present for the run owing to his move from Amherst College to the U.S. Naval Observatory.  As a result, Hiltner worked alone that summer at McDonald while Hall observed independently with the Amherst College 18" Alvan Clark refractor.  Both detected linear polarization of starlight as did Hall later in the year with the USNO 40" reflector.  The figure on top of this page shows today's version of what they measured.

Coincidentally, a more minor figure in magnetic field observations, Tom Troland, was born in 1948.  Troland was born in New London Connecticut, just a few miles from Old Lyme Connecticut, the birthplace of John Hall years earlier.  (Old Lyme, no doubt, would prefer to be known as the birthplace of John Hall rather than the original location of a disease.)  Hall was a student at Amherst College and later a faculty member.  Coincidentally, Troland was also a student at Amherst but never achieved the honor of a faculty appointment at that institution, said to be part of the "Potted Ivy League".  Below is a picture of Tom (right) and Carl Heiles (left) contemplating the awesome collecting area of the Yerkes 40" refractor, where this all began.

This conference is a celebration of 60 years of observations of the interstellar magnetic field. Troland's birthday will provide a serviceable excuse to celebrate magnetic fields with a product that goes back much further even than Hiltner and Hall - fine old Kentucky bourbon from Buffalo Trace Distillery.  Contrary to popular imagination, buffalo trace is not a waste product from the animal.  Instead, it is a wide path established by migrating buffalo that were prevalent in Kentucky centuries ago.  The current distillery is built on part of what was once such a buffalo thoroughfare.


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Last updated: 03/08/08.