G The first step in the process is to calibrate the grating, so we know the grating spacing (the distance between the openings in the grating). Sodium has two yellow lines that are very close together in wavelength at 590 nm. When light from a sodium source is passed through a particular diffraction grating, the two yellow lines overlap, looking like one line at an angle of 34.0 degrees in the first-order spectrum. What is the grating spacing