This morning - Monday, March 20th at 6:28 a.m. EDT, the Ecliptic, which is the path the Sun takes through the sky, will intersect with Earth's celestial equator. This intersection is the Vernal Equinox which will mark the end of winter and the start of the spring season in the Northern Hemisphere. At this time the Earth will reach a point in its orbit where it is neither tilted towards or away from the Sun. This will result in equal amounts of daylight for corresponding locations north and south of the equator, with the Sun passing directly overhead (at zenith) on the equator at Noon.
The Equinoxes, like the Solstices, are a result of Earth's 23.4° axial tilt. As the Earth orbits the Sun, our axial tilt remains constant and generally points in the same direction. (Note that precession will change our axial tilt and the direction of our axial tilt, though we are not talking about that here as these changes don't noticeably happen over one year). As the Earth makes its way around Sun, our 365 day year, we will reach points in our orbit, opposite each other, where Earth's tilt will be either inclined 23.4° toward or away from the Sun, these are the Solstices. In between the Solstices are points in our orbit where Earth's tilt will not be inclined toward or away from the Sun, these are the Equinoxes. The changes in our orbit as it relates to our tilt are visible to us when looking at the Sun's path across the sky. Around the Summer Solstice in June, we see the Sun pass much higher in the Northern Hemisphere sky, giving us longer days and hot temps, though around the Winter Solstice in December, we see the Sun cross the sky much lower to the horizon in the Northern Hemisphere sky, resulting in short days and cold temps. This is of course all opposite if you are in the Southern Hemisphere.
Unlike last year, we can expect sunny skies and warmer temps on the Vernal Equinox, maybe even warm enough for a picnic. So take a moment this coming Monday to step outside and welcome spring and all the heat loving zealotry that is just around the corner, including beach days, late sunsets, and fabulous nights reveling under the Milky Way.