In Greek mythology, Demeter was the daughter of two of the Titans, Cronus and Rhea, who were also the parents of Zeus, chief of the gods. Demeter was goddess of the fruitful soil and of the harvest, and was responsible for the world’s fertility. Zeus really got around among the ladies – his official wife was his sister, Hera – but he had liaisons with many other goddesses, including Demeter, and with mortal women as well. The result of his liaison with Demeter was a beautiful daughter named Persephone, who loved flowers and who was the apple of her mother’s eye.
At Zeus’ instigation, the world had been divided among himself, with responsibility for all the mortal world and the human race, his brother Poseidon, who was responsible for the seas and everything in them, and a third brother, Hades, who was god of the underworld and the dead. Now, while Poseidon was happy with his watery domain, Hades resented having to live underground and consort only with dead people and complained bitterly to Zeus.
Hades had seen Persephone picking flowers and really had the hots for her. In order to placate Hades, Zeus arranged for some exceptionally beautiful flowers to grow where Persephone couldn’t fail to see them. While the maiden was gathering the flowers, Hades suddenly appeared out of the ground, grabbed Persephone and carried her back to the underworld, where he made her his wife.
When Demeter found out what had happened to her beloved daughter, her grief was so great that she neglected the land, no plants grew and famine devastated the earth. Zeus, who didn't want the human race to die out due to famine, realized that the situation had to be remedied. Zeus’ motives were not entirely altruistic, as one of the big problems caused by the lack of food on earth was that the humans’ sacrifices to the gods had dried up.
Zeus informed Hades that Persephone had to return to Demeter in order to save the human race. Hades obeyed, but before he let the girl go, he made her eat some pomegranate seeds that had the power to force her to return to him for four months each year. Demeter was overjoyed at getting Persephone back and caused the earth to bring forth bright spring flowers and abundant fruit and grain for the harvest.
However, when Persephone had to return to the underworld each fall Demeter’s sorrow returned with the same dire results. The cold of the winter season, when the vegetation shrivels and dies, is the yearly manifestation of Demeter’s grief when her daughter is taken from her, while the annual spring rebirth reflects the Goddess’ joy at having Persephone return to her.
So now you know. Don’t you like this explanation a whole lot better than all that scientific stuff about the Earth tilting on its axis and revolving around the sun?