Mirror roof sundial calculator
Some years ago, as a student, I saw the reflection of the sun in some mirror like thing on the roof. It moved by time. That made me wonder: couldn't I make a sundial out of it, on the roof? After glueing a little mirror to the window, I started making dots on the roof, by the hour. The hour lines that I expected didn't become lines, and at first I thought there was some error in my system. Then a fellow student discovered the analemma: the sun makes kinda infinity-symbol-shaped patterns, not lines.
Since a few weeks I live in my own house. It became time to try a more serious approach. A little searching on the net lead me to 'sunearthtools': they did all the hard work of calculating sun positions. Dusting off basic trigonometry, and a few hours later this was the result. To my surprise, the calculated values matched (close enough) my roof-measured ones! The web site is fixed on the dimensions of my house and a sun path of Utrecht City center (not my house's location ;-)). The sliders can be used to fine tune the mirror angle for the nicest picture. In Holland the sun is moving away after clouds a lot this season, so practical realisation probably won't happen until around April, but I liked to share this tool already with 'the world'. Wondering if there are more of these around!