A vertical sundial (local meridian)

        This sundial is positioned on a vertical wall facing exactly due south, and its pin is pointed towards the celestial South Pole. (In the southern hemisphere the sundial should be on a north-facing wall and the pin pointed towards the celestial North Pole.)

- It is evident that, compared with a sundial positioned horizontally, the shadow sweeps round in the opposite direction (clockwise as opposed to anticlockwise in the northern hemisphere). The shadow disappears not at sunset but when the Sun passes behind the wall .

- On changing the latitude we can see that the hour-lines are displaced, and as we approach the Pole, these become bunched together and the vertical sundial becomes of little use . 

- At lower latitudes the shadow is only visible for part of the year. What must be done to tell the time during the rest of the year ? 

- The daily arcs are always conics : watch their progressive change in shape through the seasons, whilst watching the value of the declination . At the equator, what is the shape of the arc?

. To understand the apparent movement of the Sun, see also this figure .