For the Celts and other early cultures, and for many more people today than you would think, the beginning of winter is the beginning of their year. In olden times, the year began when the animals were brought in from the far pastures to warmer shelters and the tilled fields were prepared for winter. It was a lunar calendar, based on the phases of the moon and movement of the stars. Today earth-centered cultures and religions still keep to this calendar. You missed Samhainn for this year, but if you'll go to the following URL, you can find cards for all the major lunar calendar seasons.
Spring is rebirth and new growth.
Summer is a time of growing for both humankind and plants. Mother Nature just spills herself all over the land. Fall, of course is the harvest. The Celtic year climaxes with the harvest. The fruits of all the year's work are gathered in and festivals celebrate nature's bounty.