Composition 101...

Rule of thirds, Golden triangle, Golden Spiral and Golden Rectangle Division are all ways of attempting to define perfect composition.

Alfie Goodrich over at Japanorama has recently published an article on compositional rules, very interesting and well worth a look.

In addition, the long number you see above is the 'Golden Ratio' or Phi and has the habit of defining rather well images/paintings that appear to be attractive to the human eye.

Here's how to construct a 'Golden Rectangle'

1: Draw a square (here marked in red).
2: Draw a line from the midpoint of one side of the square to an opposite corner.
3: Use that line as the radius to draw an arc that defines the long dimension of the final Golden Rectangle.

Now start dividing up your favourite image with these rectangles and see what happens. Here are a few examples: