Events - Event View

Mapping the Milky Way – Mark J. Reid

     Over 2000 years ago, Hipparcus measured the distance to the Moon by triangulating from two locations across the Mediterranean Sea. However, determining distances to stars proved much more difficult. Many of the best scientists of the 16th through 18th centuries attempted to measure stellar parallax, not only to determine the scale of the cosmos but also to test Heliocentric cosmologies.  While these efforts failed, along the way they lead to many discoveries, including atmospheric refraction, precession, and aberration of light.  It was not until the 19th century that Bessel measured the first stellar parallax.

     Distance measurement in astronomy remained a difficult problem even into the early 20th century, when the nature of "spiral nebulae" was still debated.  While we now know the distances of galaxies at the edge  of the Universe, we have only just begun to measure distances accurately throughout the Milky Way.  Using the Very Long Baseline Array of radio telescopes, we now can achieve parallax accuracies of 10 micro-arcseconds!  I will present new results on parallaxes and motions of star forming regions  from the BeSSeL Survey.  These measurements address the nature of the spiral structure, size, rotation speed, and mass of the Milky Way.


Please join us for a pre-meeting dinner discussion at House of Chang, 282 Concord Ave, Cambridge, MA at 6:00pm before the meeting.