Astrometric registration of images when no WCS info is available

 Astroalign is a Python module that will try to align two stellar
 astronomical images, especially when there is no WCS information
 available.
 .
 It does so by finding similar 3-point asterisms (triangles) in both
 images and deducing the affine transformation between them.
 .
 Generic registration routines try to match feature points, using
 corner detection routines to make the point correspondence. These
 generally fail for stellar astronomical images, since stars have very
 little stable structure and so, in general, indistinguishable from
 each other. Asterism matching is more robust, and closer to the human
 way of matching stellar images.