Wait, what? Yeah, it was in the 50s today, but there's a "Winter Weather Advisory" and several inches of snow in the forecast. And doesn't spring start on the equinox, March 20th? And didn't Punxsutawney Phil say six more weeks of winter?
For those watching the skies -- astrologers, in the old days -- the most obvious events are the solstices in June and December, when the sun rises and sets in its most northerly or southerly position and reaches its highest or lowest noontime elevation; and the equinoxes in March and September, when the Sun crosses the celestial equator. (I.e., it goes from rising and setting a little north of due east and due west to rising and setting a little south of due east/west, or vice-versa)
If you know which way is north from your house (and c'mon, you probably have a GPS unit in your phone that can tell your location to a few meters, plus easy access to detailed maps and aerial photographs of your neighborhood, you ought to know!) you can watch this happen over the course of the year.
But for those watching the earth, changes in the behavior of plants and animals were more important. Thus we have the "agricultural seasons" that both the old Celtic calendar recognized, where the seasons started on or around the "cross-quarter" days:
- Imbolc, which survives to us as Groundhog Day and Candlemas, February 2nd. Or 1st, depending on how you count. In the old days, the day began at sunset. Note its proximity to Chinese/Lunar New Year, the Spring Festival in China. It may be that the question of whether spring starts now, or on the equinox in six weeks, is behind the tradition of appealing to the groundhog. (Some say that in Europe, a badger or bear was the prognosticator.)
- Beltane, "Mayday", May 1st, the start of summer. Thus, the summer solstice, halfway between Beltane and Lammas is "mid-summer". (Nobody seems to take this one as May 2nd or April 30th.)
- Lammas or Lughnasadh, August 2nd (or 1st), the festival of the first harvest and the start of autumn;
- and Samhain, which survives to us as Halloween, October 31st (or November 1st), the start of winter.
Of course plants and animals don't count days (mostly) in making their plans, so some communities celebrated these festivals a little later or earlier, depending on when the signs appeared. And the calendar has shifted over the years (which is why Christmas is on December 25th rather than December 21). And of course these days we tend to do any celebrations on a nearby weekend anyway. So the exact date can be argued, but most Neopagans use more-or-less these dates.
In ancient agricultural societies, the lambing season began around this time. The days are perceptibly getting longer, and buds are apparent on the trees. The UK's Royal Horticultural Society says that in February,
...there are signs of the approaching spring, with bulbs appearing and birds and wildlife waking up as light levels and temperatures increase. There's plenty to do indoors this month, all in preparation for the season ahead. Outdoors, the garden is coming to life again, and its time to prune shrubs, such as Wisteria.
It's still cold, but under the surface the "energy" of the year is beginning to change. There's nothing definite in the skies to mark it, but on the earth, you can see it if you look.
So. Happy Spring!