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GOLF 4-3-9 Antarctica Expedition 2010


Puzzles abound, even before we get to Antarctica. Our delay gives us more opportunity to explore Christchurch, and I happened to run into a sundial in the Botanical Garden. Different from the sundials in the US, the dial goes counterclockwise, where One o’clock is to the left of noon.

So, why the heck does the sun go the other way around in Christchurch than in San Diego?

It all comes down to the fact that the sun rises in the east and it is straight up at noon at the equator. (This changes a bit through the seasons as the earth tilts relative to its orbit, but we can ignore this for now.) With that, you can figure out how you see the sun moving when you are in the northern hemisphere and in the southern hemisphere.

It is easy for most of us to imagine this for our usual northern hemisphere perspective. If you are looking for the sun you face South, and if it is in the morning you look more towards the east and in the evening you look more towards the west. So the sun goes from left to right, that is clockwise, and with the sun the shadow of your body also moves left to right, because it is in the same sense of motion. Northern hemisphere sundials go clockwise. Well done, Einstein!

Now imagine yourself in the southern hemisphere. If you can’t find the sun right away, try looking north. If it is in the morning you have to look to the east of north, which will be to your right when you are facing north, and in the afternoon you look more to the west. So, the sun actually moves from your right to your left as you are facing it. Last time I checked that was counterclockwise. And, if you are engineering a sundial you have to make it counterclockwise! Cheers, you have done it. Weird, nevertheless.

Hotel Sierra from Christchurch