Summer Solstice (a sunrise experiment)

This is an experiment. Line up a nail held vertically against the rising sun on the Summer solstice. I want to see if I can use Photosynth to help me line up EXACTLY where the sunrises on the summer solstice, and later on the Spring equinox. Ultimately, when I am comfortable I have it right, I want to inlay some bronze markers on my balcony to serve as a kind of astronomical pointer... my own Menorcan Tabla...

Next time, I'll use a proper plumb line, clamp it steady over my mark, and add a filter to the camera so I can see the solar sphere...