It s a really really long discussion In short It is interpretation rather than bare plot description to assert that the sunlight is what triggers the signal and as such saying so should be avoided in the plot section However in sections of the article devoted to interpretation of the film discussion of this would be appropriate That s the main point Furthermore given the position of Clavius on the moon and the position of the sun as the shuttle approaches the moon monolith it s reasonably evident that the final shot of the sun directly over the monolith is impossible though sunlight touching the monolith from another angle per se might be So it could be something in someone s mind