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Physics Colloquium - Dr. James Hilton

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Tuesday, April 24, 2018, 4 pm

This is a past event.

Sunsets, Telescopes, and Buoys: The Problem of the Surface Layer in Atmospheric Refraction

Abstract:

The physics of atmospheric refraction is well understood, but applying the theory to practical applications, such as celestial navigation, is difficult. One obstacle to applying the theory is lack of a practical method to intuit the change in temperature with height within the surface layer, the portion of the atmosphere within about 200 m of the Earth's surface. The effect of the surface layer on refraction can most dramatically be seen in observations of sunrise and sunset. Few quantitative data are available that include all the atmospheric parameters required to analyze the surface layer effect. One such data set consists of the sunset observations made at Mount Wilson from March 1987 through November 1991. Analysis of these data supplemented with data from a weather buoy located in the vicinity of the horizon illustrate the effect of the surface layer on refraction near the horizon and the difficulty in extracting a set of rules for improving predictions of near horizon phenomena from such limited data.

Bio:

Dr. James Hilton grew up in Texas. He graduated from Rice University with a B.A. in physics in 1979 and earned his Ph.D. in astronomy from the University of Texas at Austin in 1990. He has been with the U.S. Naval Observatory, primarily in the Astronomical Applications Department, since 1986. His primary interest is predictions of the places and visual aspects of the planets. He has been working on the problem of atmospheric refraction in an effort to improve the apparent places of celestial objects since 2009. He lives in southern Oregon.

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