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.
The typical common cold incubation period is from two to five days, but symptoms can appear in as little as ten hours after the virus first enters the nose.The range of the common cold incubation period may be explained by the number of different viruses that can cause common cold symptoms.It is known that some viruses produce symptoms of disease more quickly than others and several hundred different viruses have been associated with the common cold.he range of the common cold incubation period may be explained by the number of different viruses that can cause common cold symptoms. It is known that some viruses produce symptoms of disease more quickly than others and several hundred different viruses have been associated with the common cold.