I never really noticed it until we started planting and growing sunflowers - but these guys have a knack of tracking and following sunlight (or artificial light of the same wavelength I guess).
The flowers themselves behave like radio/satellite dishes that look up and actually follow the sun. As if it were trying to get the 'best signal' :-)
And what amazed us more was this little gem that we harvested from our backyard. When we got it in, the thing was looking downwards, but we didn't pay too much attention to that detail, and we placed it in a vase and on the dining table.
And just the other night, we were surprised to see the flower was not in the 'nodded' position but has reared up its 'head' and was 'looking' towards our dining lamp/light! So even with the flower already cut from the main stem, this behavior still exhibits.
Nature sure is quite impressive!