White light and a diffraction grating

Today we looked at the white light from an overhead projector through a diffraction grating. The central spot will always be white because all wavelengths go together in the straight on direction. Since wavelength is colour, you get white because that's what all colours of light add up to give. However to the sides, you only get a colour where the angle means that the path difference is measured in whole wavelengths. That splits the colours up. Violet has a smaller wavelength so it doesn't have to bend as far to the side to have an integer path difference. Red with its longer wavelength bends out further before this happens. Hence the spectrum with violet closest to the centre and red furthest out. It is clearest under the two satellite white spots that are reminiscent of sun dogs. I'm not sure why they are there. Sun dogs are a refraction effect so the colours in a sun dog are the other way round. There were other interesting artifacts in the photographs caused by light leakage.