Posted on 03/19/2005 7:08:25 PM PST by Puckster
In the years 2008 and 2012, those living in Alaska, Hawaii and the Pacific, Mountain and Central time zones will see spring begin even earlier: on March 19. And in 2016, it will start on March 19 for the entire United States.
There are a few reasons why seasonal dates can vary from year to year.
1. A year is not an even number of days and neither are the seasons. To try and achieve a value as close as possible to the exact length of the year, our Gregorian Calendar was constructed to give a close approximation to the tropical year which is the actual length of time it takes for the Earth to complete one orbit around the Sun. It eliminates leap days in century years not evenly divisible by 400, such 1700, 1800, and 2100, and millennium years that are divisible by 4,000, such as 8000 and 12000. 2. Another reason is that the Earth’s elliptical orbit is changing its orientation relative to the Sun (it skews), 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 Earth reaches each 90-degree location in its orbit around the Sun. 3. 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:
Winter: 88.994 days
Spring: 92.758 days
Summer: 93.651 days
Autumn: 89.842 days
As you can see, the warm seasons, spring and summer, combined are 7.573 days longer than the colder seasons, fall and winter (good news for warm weather admirers).
Ping me when you do.
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