There's a nice animated .gif image recently added to the Wikimedia Foundation Commons which gives a good introduction to a sun shot. The image is licensed under CC-by 2.5, by commons user Alvesgaspar.
Neat graphic, but backwards. Yes it can be done for the sun, moon and maybe the planets, but generally it's easier to point the zeroed sextant at the celestial body, then bring the image down to the horizon.