![]() ![]() Why? There are several reasons, but the one that’s easy to understand is: the Sun doesn’t follow a human calendar! You may have noticed that the first day of spring is on a different date than when you were younger. Learn more in our article about the “ Reason for the Seasons.” Credit: NAA Why Has the Date Changed for the Start of Seasons? And when the South Pole tilts toward the Sun, it’s winter in the Northern Hemisphere. When the North Pole tilts toward the Sun, it’s summer in the Northern Hemisphere. So, as the Earth orbits the Sun over the 12 months of the year, different parts of Earth get the Sun’s direct rays. The axis is always tilted in the same direction. It’s the Earth’s tilted axis that causes the seasons. It’s commonly assumed that the warmer seasons happen because Earth is nearer the Sun (and the colder seasons happen when Earth is farther from the Sun). Nope. The Old Farmer’s Almanac is an astronomical “calendar of the heavens,” so our book has long followed the astronomical definition of the seasons based on the Sun and Earth! What Causes the Seasons? According to this definition, each season begins on the first of a particular month and lasts for three months: Spring begins on March 1, summer on June 1, autumn on September 1, and winter on December 1. Climate scientists and meteorologists created this definition to make it easier to keep records of the weather, since the start of each meteorological season doesn’t change from year to year. In contrast, the meteorological start of a season is based on the annual temperature cycle and the 12-month calendar. ![]() 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. More specifically, the start of each season is marked by either a solstice (for winter and summer) or an equinox (for spring and autumn).
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