Because the world is round
Because the world is round
It blows my mind
© The Beatles, 1969
A few days ago Susan and I were basking in the sunshine in Maui, where we wore short-sleeved shirts and felt the warmth of the 86F Hawaiian air. At that very moment a phone call from our daughter informed us that it was snowing in the hills around Kenwood. I thought, “This happens because the world is round.”
It has been known for a few millennia that during a lunar eclipse the earth casts a round shadow on the moon – something it could not do if it were flat (except that a flat disc, like a coin, can also cast a round shadow if the sunlight comes from the correct angle). I thought, “What other remarkable things do we take for granted that are possible because the earth is round – like a sphere?”
Well, temperature differences between different localities, for one thing. Maui is at latitude 21N, whereas Kenwood is at 38N, and the sun will shine from higher in the tropical sky than in the wine country sky. At extremely high latitudes (above the Arctic and Antarctic circles) the sun never gets very high in the sky, resulting in even more extreme temperature differences.
The heated air in the tropics tends to rise, and is replaced by cooler, denser air rushing in from the colder, higher latitudes. When masses of air move we call it “wind,” and the temperature difference between the poles and equator is the main engine that drives our weather phenomena. Currents in the solar heated oceans result from warm water rising, and being replaced by colder water from the ocean depths, analogous to winds in the atmosphere. These effects are complicated by the earth’s rotation, which gives a spin to moving air, resulting not only in extremes like hurricanes, but also in more gentle weather changes.
If the earth were flat, and spinning like a long-playing record, there would be very little variation due to differential temperatures. On the other hand, a flat earth rotating like a flipped coin could make for more extreme daily temperature variation.
Location on a sphere effects not only latitude but also longitude. Changes in time zones exist because the sun cannot shine at the same angle at every point on a sphere. Parts of the sphere receive more direct sunlight than others, and in fact, at any moment in time, half of our sphere is always in shadow. We call the shadow of the earth “night,” and different parts of the earth experience night at different moments in real time. Thus, a Maui sunrise is about two hours later than a Kenwood, California, sunrise, which in turn is about eight hours later than a sunrise in London. This time difference would not exist on a flat earth.
The seasons themselves exist partly because of the curvature of the earth, as well as its tilt, and give rise to the peculiar circumstance that the seasons in the northern and southern hemispheres are reversed. The higher the latitude, the more extreme the difference. Above the Arctic Circle the residents are now experiencing a long winter night, and the penguins of Antarctica are basking in their midnight sun.
All of these, and much more, happen because the world is round. Small wonder it blows my mind!
© February 25, 2011, by Nathan B. Miron, Ph.D.