The last course stirred up some healthy discussion about the difference between the sun’s summer and winter arcs in the sky. The arcs are actually very similar, because they are parallel, but in our winter the arc is displaced to the south. However, the effect this has on shadows is more interesting and beguiling. The arc traced by shadows over the year are not parallel, but change quite significantly from summer to winter. This is because the sun rises north of us in summer and south of us in winter. The effect this has on shadows is quite counter-intuitive, but no less fascinating for it. The chalk line in this photo shows how the shadow from the edge of a flower tub moved this morning. In the summer it would have curved the other way and closer to the pot.
Tags: concave shadows, convex shadows, shadow stick, solstice, sun arc
