Happy first day of spring! And thanks to Gary Eagle for sharing with us this beautiful bluebird scene from the Hunter Creek Trail in Reno, Nevada.
A great number to remember today is 23.5. The Earth's axis has a 23.5-degree tilt, which causes our seasons to change as we circle the Sun. When the northern half of Earth is tilted toward the Sun, we in the Northern Hemisphere enjoy spring and summer; when it's tilted away from the Sun, we have fall and winter. (The seasons are opposite for those of you in the Southern Hemisphere.) Today—the spring solstice—is one of only two days (along with the autumnal solstice) when the Earth's tilt is neither toward nor away from the Sun. It's a transition day. From tomorrow until late September, we on the northern half of the globe will be leaning toward the Sun, catching its rays more fully.
The Earth's tilt varies by a degree or two over 40,000-year cycles, so the length and intensity of the seasons can change in certain locations over that time. All the planets in our solar system have some degree of tilt, ranging from Mercury at .03 degrees (no seasons on that tiny planet) to Uranus at 98 degrees of tilt (the Northern hemisphere there gets 42 years of summer followed by 42 years of winter—yikes!).
Here's to our good fortune in not having 42 straight years of winter or a different axis angle that would have tilted the delicate balance of life on our planet and prevented it from ever becoming our home sweet home. —Craig Neff and Pamelia Markwood