For ages, astronomers have sought to "envisage" the stars — that is, to imagine them as if they were close up, at the same distance from the viewer as ordinary three-dimensional objects on earth. This has meant that all astronomers, particularly if they wished to communicate their sky-images to others, have had to think of asterisms in the forms of traditional schemata, the accepted conventions of picture-making in the astronomer's native culture at a given historical time.