The Solstices
The meaning of the word "solstice" comes from the Latin sol, meaning "sun," and sistere, meaning "to stand still." During the summer solstice, the sun rises to its highest point in the sky and seems to "stand still" for a period of time. The summer solstice (usually June 21/22 if you live in the northern hemisphere, Dec 21/22 for the south) is the longest day of the year, while winter solstice (usually December 21/22 for the northern hemisphere, and June 21/22 for the south) is the shortest.
The sun has often been used as a way to know when to plant crops or harvest them, a way to chart the seasons, and a way to tell time. Hence, the summer and winter solstices, representing a turning point in the seasons were commonly considered a time of celebration and of respect for the earth.
The seasons of the year are caused by the 23.5 degree tilt of the Earth's axis. For half of every year the southern hemisphere is the most exposed to the sun, while for the other half the northern hemisphere gets to bask in the sun. Summer solstice occurs in the middle of this half of the "sun-time" for each hemisphere. In the opposite half it is winter solstice. The equinoxes occur at the two points when the sun is equally shining on the north and south hemispheres. The equinoxes usually occur on March 21/22 and Sept 22/23. I might try to find some information about them later, but for now this is just the solstices:
Summer Solstice
Summer Solstice is also know as Alban Heflin, Alben Heruin, All-couples day, Feast of Epona, Feill-Sheathain, Gathering Day, Johannistag, Litha, Midsummer's Day, Sonnwend, Thing-Tide, and Vestalia.
Summer solstice was a time to harvest certain crops, or participate in rituals believed to help other crops grow. In ancient Europe couples would jump over a bonfire; it was believed that the crops would grow as high as they could leap. In Rome the midsummer festival was called "Vestalia" and held in honor of Vesta, goddess of the hearth (Or, as she was called by the Greeks, Hestia).
Between plantings and harvestings, the time around the Summer Solstice was aslo a popular time for weddings. The first moon in June is called the "Honey Moon" and was believed to be the best time to gather honey. Often, couples would be fed this honey for the first month of their marriage to encourage love and fertility. While this practice is no longer done, it lives on today in the name of the holiday after a wedding: the honeymoon.
Winter Solstice
Winter solstice gave people reason to celebrate because it meant that the days would start to get longer, until eventually the warmer season arrived. The concept of birth and death/rebirth is associated with the winter solstice. Because no one had elaborate instruments to detect the solstice the change in elevation of the sun's path was generally not noticed until a few days after the true solstice. Many celebrations were time for about December 25th (What a coincidence, eh?).
In ancient Greece the solstice was called Leneae (Festival of the Wild Women). In very ancient times, a man represnting Dionysos, the harvest god, was torn to pieces and eaten by a gang of women. Later, this was changed to simply killing a goat while the women acted as funeral mourners.
In ancient Rome a festival called Saturnalia, several feast days in honor of Saturn, took place from Dec 17 to 23. The winter solstice was regarded as the nativity of such god-men/saviours as Appolo, Attis, Baal, Dionysus, Helios, Hercules, Horus, Jesus, Mithra, Osiris, Perseus, and Theseus, those festivals were blended by Emperor Aurelian (270-275 CE) into a single festival, "Birthday of the Unconquered Sun" that took place on Dec 25th.
Obviously, Christmas is another holiday celebrated at this time. The date of December 25th was chosen in about the 4th century probably because it was already regarded throughout the Roman empire as the birthday of various pagan gods. The date is not the only thing Christmas borrowed from other cultures; many symbols and practices associated with Christmas are of Pagan origin such as holly, ivy, mistletoe, the yule log, the giving of gifts, decorating evergreen trees, and magical reindeer. Hmm, nothing about evil goats though ;)