Scientists believe that the Earth's orbit gradually changes from being elliptical to being nearly circular and then back to elliptical in a period of about 100,000 years. This causes global climatic change. The more circular the Earth's orbit, the less the difference in ---magnetic force on the Earth's closest and farthest locations from the sun gravitational pull on the Earth's closest and farthest locations from the sun solar energy received at the Earth's closest and farthest locations from the sun duration of days and nights at the Earth's closest and farthest locations from the sun