This gradually rotating starscape represents the Milky Way seen from Earth. I based it on a published projection from Axel Mellinger, featured in APOD. The picture appears to be given in Mollweide projection, which is an equal-area projection. At first, the peculiarities of that projection are straightened out by stretching the image horizontally to fill the entire canvas data area. The projection also probably introduces small distortions vertically, but these seem too minor to bother with.
A projection plane is calculated as the tangent plane of a unit sphere, and intersection against milky way image is calculated. This determines the pixel's color.