Here are two heatmaps, representing the Sun's zenith angle $\theta$ and azimuth angle $\phi$ respectively, at a point on Earth's surface, as a function of the time of year and time of day (varying along the horizontal and vertical axes, respectively).

Zenith angle refers to the angle from directly overhead. In the heatmap shown, white means $\theta=0^{\circ}$ (directly overhead), and black means $\theta > 90^{\circ}$ (at or below the horizon).

Azimuth angle refers to the angle of rotation from true north. Here we use a color map which begins as red at $\phi = 0^{\circ}$, and cycles through green, blue, and back to red at $\phi = 360^{\circ}$.

The slider below controls the latitude of the reference point on earth, and it is assumed that the earth has an axial tilt of $23^{\circ}$.

TODO Explain how one derives this heatmap, with a diagram.

TODO Explain how one can use this. How it came up while pondering solar panel angles.