Because we can not resolve stars up close, the need for masses and radii of stars remains a key to a wide variety of astrophysical problems. The most accurate way of determining these quantities is by spectroscopic measurements of the line-of-sight ("radial") velocities of eclipsing binary stars with time as they revolve around one another in orbit alternately blocking the light from one another. The Principal Investigator (PI) has devoted his career to these measurements, particularly to the measurement of orbits around massive stars. The PI will extend this work for the next two years to stars with masses just less than the Sun's and will use modern Charge Coupled Device detectors to measure their orbital velocities more accurately than from photographic spectra and for fainter stars. This work is expected to help place the Sun in the context of the physical parameters of similar stars.
