1. The problem statement, all variables and given/known data Question: Blue light of wavelength 485.6nm from a star is incident normally on a diffraction grating. The light is diffracted into a number of beams, as shown in Fig 5.4.(attached) The angular separation of the two second-order beams is 45.72 degrees. Calculate the number of lines per millimetre on the grating. 2. Relevant equations 3. The attempt at a solution I genuinely do not know where to start the question. I know the formula for Young's double slit experiment however this does not seem to relate to it at all. Any suggestions for starting the question would be really appreciated.