Measuring the Sizes of Stars: Fringe Benefits of Interferometry
Stars, other than the Sun, appear to our unaided eyes aspoints of light. Large telescopes show an image whose sizeis dictated by refractive index irregularities in the Earth’s atmosphere.The size of this blurring is much greater than thatof the star, and hence it is difficult to measure the stellar size.Fizeau showed how one might overcome this limitation usingthe two-slit interference technique. It was Michelson whocarried out this programme and made the first direct measurementof the giant star Betelguse in the constellation ofOrion. His value for the angular diameter, 47 milliarcsecondsor 2.6×10−7 radians, was completely confirmed by laterwork following his methods. The key concept introduced was
‘fringe visibility’, which turned out to be very fruitful in thelater development of optics as well as astronomy.
Volume 26 | Issue 10