ALT The planet’s light environment. Panel A) shows the incidence of the sun shining on at the equator and in the far north hemisphere. B) shows the incidence of the sun during the northern hemisphere summer/southern hemisphere winter and the sun on the planet during the southern hemisphere summer/northern hemisphere winter. C) shows a graph (months x-axis, daily insolation y-axis) with curves for the solar insolation through the year at 20deg, 40deg, 60deg and 80deg north. Daily insolation varies little in the tropics, but at 80deg north, there is virtually no daily sun from October-February. D) shows the difference in the angle of the sun over a 24h period on the equinox at 20deg and 80deg north. Day length is the same at all latitudes but in the tropics the sun rises high in the sky, while at 80deg north the sun is only 20deg about the horizon at midday. E) shows the solar elevation of the sun on the summer and winter solstices at 80deg north