Today is the March equinox — we call it the vernal or spring equinox in the northern hemisphere, but in the southern hemisphere it’s the autumnal or fall equinox. The vernal equinox is the first day of spring (astronomically speaking), just as the autumnal equinox is the first day of fall (astronomically speaking).
❡ Little lessons: “‘Vernal’ and ‘autumnal’ are beautiful words. Let’s look them up in our dictionary (riverhouses.org/books).”
Whenever you’re investigating things temporal or calendrical, timeanddate.com is always a good place to start:
The seasons occur because the earth’s axis of daily rotation is not quite perpendicular to the plane of the earth’s annual orbit around the sun (it’s tilted by about 23º). The two solstices occur at the points in the annual orbit when the axis is tilted most directly away from the sun (in December, on the first day of northern-hemisphere winter), and most directly toward the sun (in June, on the first day of northern-hemisphere summer). The two equinoxes, in March and September, occur at the points in the annual orbit when the earth’s axis is “sideways” to the sun (so to speak), making the intervals of daylight and darkness equal (or very nearly so).
NASA has a fun educational crossword puzzle for kids that’s filled with seasonal and astronomical vocabulary — solstices, equinoxes, and more.