WEST MICHIGAN — Spring arrives tomorrow folks! When winter officially changes into spring at 11:50 p.m. EDT, Thursday, March 19, that will be the earliest start to spring in 124 years!
According to the Farmers' Almanac, 1896 was the last time spring arrived that early. The first day of spring usually arrives on March 20th or 21st, but it’s coming early this year as a variety of factors fall into place.
The first is that a year is not an even number of days and neither are the seasons, according to the almanac. 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.
Also (according to the Farmers' Almanac), the pull of gravity from the other planets affects the location of the earth in its orbit. The current seasonal lengths for the Northern Hemisphere are spring, 92.771 days; summer, 93.641 days; autumn, 89.834 days; and winter, 88.994 days. However, spring is currently being reduced by approximately one minute per year and winter by about one-half a minute per year. Summer is gaining the minute lost from spring, and autumn is gaining the half a minute lost from winter. Winter is the shortest astronomical season, and with its seasonal duration continuing to decrease, it is expected to attain its minimum value — 88.71 days — by about the year 3500.
According to the Old Farmer's Almanac, the astronomical start to a season is based on the position of the Earth in relation to the Sun. More specifically, the start of each season is marked by either a solstice (for winter and summer) or an equinox (for spring and autumn). A solstice is when the Sun reaches the most southerly or northerly point in the sky, while an equinox is when the Sun passes over Earth’s equator. Because of leap years, the dates of the equinoxes and solstices can shift by a day or two over time, causing the start dates of the seasons to shift, too.
On the vernal (spring) equinox, day and night are each approximately 12 hours long (with the actual time of equal day and night, in the Northern Hemisphere, occurring a few days before the vernal equinox). The Sun crosses the celestial equator going northward. It rises exactly due east and sets exactly due west.