When is the Real First Day of Spring – March 20th or 21st?
Traditionally, we’ve celebrated the beginning of spring on March 21, but astronomers and calendar manufacturers alike now say that the spring season starts one day earlier, March 20, in all time zones in North America. How could the first day of spring change from year to year? There are a few reasons why seasonal dates can vary from year to year. The first is that a year is not an even number of days and neither are the seasons. Another reason is that the earth’s elliptical orbit is changing its orientation (skew), which causes the earth’s axis to constantly point in a different direction, called precession. Since the seasons are defined as beginning at strict 90-degree intervals, these positional changes affect the time the earth reaches each 90-degree location in its orbit around the sun. The pull of gravity from the other planets also affects the location of the earth in its orbit. The current seasonal lengths for the Northern Hemisphere are: Summer – 93.641 days Autumn – 89.834 da
