The Earth's orbit is very close to being a perfect circle, but not quite. It is somewhat elliptical, which means that the distance between the Earth and the Sun varies over the course of the year. This effect is too weak to cause the seasons, but it might have some influence over their severity.
@burcidi-- I don't think so. Three weeks is too long as an incubation period for a common cold. The incubation period is usually a few days in most people, but it can be up to a week. If you had said two weeks, then I would have said maybe, but I doubt that you picked up the cold from your friend.ymptoms can appear in just a few hours or as long as 10 days after exposure. The average incubation period is one to three days. Medications do not affect the incubation of a cold, nor do they eradicate it unless it is accompanied by a bacterial infection.
When you get a cold, symptoms can vary and the duration of your illness is unpredictable, but most colds last between 7 and 10 days. However, they can last anywhere from 2 days to 2 weeks. How Long Is a Cold's Incubation Period? After you are exposed to a cold virus, symptoms typically start to appear 2 to 3 days later. This is called the incubation period. Every illness has an incubation period but how long it is will differ depending on the cause. How Long Are Colds Contagious?