" 

 :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.  "