!Pressure melting and skating

In this section of Resonance, we invite readers to pose questions likely to be raised in a classroom situation. We may suggest strategies for dealing with them, or invite responses, or both. “Classroom” is equally a forum for raising broader issues and sharing personal experiences and viewpoints on matters related to teaching and learning science.     

Measuring the sizes of stars

Stars, other than the Sun, appear to our unaided eyes as points of light. Large telescopes show an image whose size is dictated by refractive index irregularities in the Earth’s atmosphere. The size of this blurring is much greater than that of the star, and hence it is difficult to measure the stellar size. Fizeau showed how one might overcome this limitation using the two-slit interference technique. It was Michelson who carried out this programme and made the first direct measurement of the giant star Betelguse in the constellation of Orion. His value for the angular diameter, 47 milliarcseconds or 2.6×10^?7 radians, was completely confirmed by later work following his methods. The key concept introduced was ‘fringe visibility’, which turned out to be very fruitful in the later development of optics as well as astronomy.     

The Rayleigh–Taylor instability among the stars

The instability of the interface separating a denser fluid from a lighter one below it has applications to the surroundings of massive stars – both when they are born and when they die.