There is a point on the earth that is closest to the Sun. This is called the sub solar point. Incidentally, this is also the point that has zero shadow at that very instance. The way the earth rotates and revolves around the sun, causes this point to trace out a very interesting path. It makes a complete round about the globe near a latitude and slightly changes it's latitude with every rotation of the earth. This results in a spiral wrapped around the globe, between the tropic of Cancer and Capricorn. This spiral cycle repeats every year!