Meteorologists use what they know - temperature. For them, Winter is the three coldest months, December, January, February. Summer is the three hottest months, June through August.
People who are not meteorologists and don't spend their lives looking up and who don't get outside enough tend to go with the astronomers, mostly because that is what they hear on the television.
|The End of Autumn. Hello Winter.|
When the snow starts to melt and the first green appears, it is Spring. Putting it on a western calendar would mark it as the start of February, now called Groundhog Day, Candlemass, Imbolc. That actually arrives half-way between the winter solstice and the spring equinox. It takes the Earth a while to warm up.
First growth is over and flowers appear at the start of Summer, around May 1st, Mayday or Beltane.
Fruit and grain start to ripen as the days get noticeably shorter, at the start of August. August 1 is called Lammas, from loaf mass, the blessing of the first new bread. Now we are in nature's Autumn.
And then, around the end of October, the colorful leaves fall, the gardens die, we celebrate Samhain or All Hallows Eve (Hallowe'en, the first harvest thanksgiving), and winter arrives. Sometime in the next week a storm will sweep through, the trees will be swept bare. Hello Winter.