Spring is here. Birds were chirping as soon as the sun started coming up this morning. We had a little rain yesterday, but today is a day of a steady, light rain. We started getting green grass last week, the buds were starting to form and open this past weekend, and I saw a few flowers. With today's rain, I'm sure everything will be sprouting and getting greener. Geese have long left the area. Winter is officially over today, at least on paper.
Some history about when the first day of spring is every year:
The March equinox occurs the moment the sun crosses the celestial equator – the imaginary line in the sky above the Earth’s equator – from south to north. This happens either on March 19, 20 or 21 every year. On any other day of the year, the Earth's axis tilts a little away from or towards the Sun. But on the two equinoxes, the Earth's axis neither tilts away from nor towards the Sun.
Today is the spring or vernal equinox, with the sun shining directly on the equator, and when the 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.
There are also the summer solstice, which is the longest day of the year, and the Sun reaches its most northern point in the sky at local noon. After this date, the days start getting shorter.
During fall, or autumnal equinox, day and night are each about 12 hours long (with the actual time of equal day and night, in the Northern Hemisphere, occurring a few days after the autumnal equinox). The Sun crosses the celestial equator going southward; it rises exactly due east and sets exactly due west.
And winter solstice is the shortest day of the year, when the Sun reaches its most southern point in the sky at local noon. After this date, the days start getting longer.
The four seasons are determined by changing sunlight (not heat!)—which is determined by how our planet orbits the Sun and the tilt of its axis.