I'm a big fan of LaTeX and PSTricks and I use them often to create diagrams and graphs for my various maths and astronomy lecture notes. But to create this lunar phase diagram it was much more convenient to use another package called TikZ!
It's a pretty standard diagram; sunlight is shown streaming from the right. The Earth is at the centre with the moon shown in a (blue) circular orbit and presented at various positions around the orbit. The phase of the moon (the shape of the illuminated portion we see from Earth) is shown outside the orbit. I added some arrows and arcs to show the traditional waxing (growing larger) and waning (growing smaller) sections of the orbit and finally, the number of days since new moon.
Technical details of the code below the fold.
Dr Adrian Jannetta
Guitar strummin' explorer of the universe. Mild mannered maths teacher by day and astronomer by night.