"...dates are not exact. Some years the sun will enter or leave a sign one or two days before or after the dates you se published. This is because the Sun does not travel at the exactsame speed year in and year out. There are slight changes in its forward motion due to the position of the earth. Also, at certain times of the year the sun travels faster than at other times (for example, the sun is traveling four minutes faster per day in early January than in early June)."