The Zodiac derives from the yearly path Sol (our sun) seemingly takes across particular constellations, which is why there are twelve astrological signs. Or, at least, there were 12... when the Zodiac was created a few thousand years ago. In the solar cycle, there are 12 months, but the lunar cycle has 13. The Mayans recognized 13 star signs. 13 was significant in ancient Celtic society, considered sacred as they revered the feminine and therefore the lunar cycle and Luna (our moon). The sun is a masculine symbol; the moon, feminine. So our male dominated society elevates and operates by the sun. For habit and convenience, 12 twelve signs of the Zodiac (Western or Chinese) have been accepted and perpetuated as constant and unchanging. But since the impact of a 26,000 year long wobble called "precession" has caused Earth's orientation to gradually shift slightly, Sol passes over a thirteenth constellation between Scorpio and Sagittarius- from November 30 to December 17: Ophiuchus (The Serpent Bearer/Holder).

Technically, this makes Ophiuchus the twelfth sign, and Sagittarius the thirteenth.
Consequently, this alteration of the cycle inevitably skews astrological alignment and thus its influences on and application to us; as well as variances in the ebb and flow of cosmic energies, electromagnetic and gravitational forces we are exposed to.

Metaphorically, could the appearance of snake wielding Ophiuchus in our sky be an auspicious omen, denoting an imminent and unfolding transitional time of healing and enlightenment? Maybe this represents the prophesied return of Christ?
Despite Christianity's negative associations, the snake or serpent has long been a symbol of knowledge, wisdom and healing in the religious and occult traditions of many cultures; especially ancient societies. The Dragon, Ouroboros, Asclepius and Caduceus iconography prominent among them. But even the Biblical serpent can be interpreted positively as a harbinger of awareness or consciousness.

Ophiuchus, an alias or equivalent of Aesclepius, is the Greek god of healing.

Supposedly based on a real person, he was responsible for allegedly resurrecting the dead with his medical skill through a myth involving insight from a serpent. It is said that Asclepius accomplished this feat with an herb that he witnessed a serpent using to revive another serpent that Asclepius had killed with his staff.
Hence, the Asclepius icon (staff wrapped with single snake) and then later Caduceus (staff entwined with two snakes) becoming universal symbols of medicine or hospitals.
The Caduceus also has connections with Hermes in Greek myth, and Mercury in Roman myth, signifying a messenger of the gods. It has been observed that the image resembles a double helix. Quetzalcoatl, the Meso-American inspiration god, appeared as a feathered serpent. Ancient Egyptians also had a version of Ophiuchus, whom they knew as Imhotep... so perhaps, like Christ, this is an example of a recurring mythic archetype... and like the story of Saint Nick, was exaggerated and transfigured.
It is interesting to note that in the Norse depiction of Armageddon- called by them Ragnarok, a man-god- Thor- wrestles with a giant serpent named Jormungand for the fate of the world. And in the TV show Millennium, the logo of a group who sought to control the end of the world was the Ouroboros.

Snake oil, familiar in pop-culture as a folk tale image of miracle salve to cure any pain or illness, is a euphemism for a product sold with exaggerated or fraudulent claims; but is a real Chinese remedy used to sooth joint pain.
So what we have here is a theme of apocalypse- in both senses of the word, in conjunction with rebirth or renewal.

December 21 is the winter solstice, an important occasion for the Celts because it was a time of rebirth, and the last chance to feast before a hazardous winter set in.
The celebration is known as Yule, derived from the Norse word for wheel- which symbolized a turning point from darkness into light as the length of night begins to shorten and the length of days increase. December 21, 2012.

In a leap year, and 13 years after 1999. Astronomers tell us that the sun's path will visually intersect with the Galactic equator- a phenomenon I'm told is very rare (once every 25,920 years) and that the Mayan mythologically identify as The Sacred Tree. This forms a kind of celestial crossroads where the sun in Winter Solstice converges with the center of our galaxy. Ophiuchus leads into Saggitarus, a constellation which research reveals points toward the galactic center around this time through an area of a dark rift in the Milky Way. Which sounds a lot like Road to Xibalba and the Tree of Life mentioned in the movie The Fountain.
According to (translation of) The Mayan Mesoamerican Long Count calendar- which would mark its thirteenth and final cycle before resetting to 0 (13.0.0.0), in this age of Ophiuchus, this date may also signify the impending end of the world. Because the Mayan calendar ends then and there, many people are wondering and anticipating- as they did with the year 2000 (and we all saw how that turned out)- about what this means. However, 2000 could have been a miscalculation or approximation for 2012. Or a postponement.

A calendar that reportedly began at 3114 B.C, approximately the same time period established in the Egyptian Long Count Calendar.... under 6000 years ago- the point when many contemporary Christians claim the world began. So perhaps, at least symbolically or conceptually, this was the time of our Genesis, when the world as we know it started.

How the Mayans and Egyptians determined such things involves a math way beyond my pay grade, and is another matter entirely. Clearly, the fact that these allegedly less advanced peoples had access to this kind of information shows they knew something about the nature of the universe- of life, death and time- that we do not. Enough so that they could predict or project metaphysical and archetypal manifestations. They recognized and accepted that history and nature repeat in celestial cycles, which even Nietzsche noted in his idea of Eternal Recurrence.
Could Atlantis have existed and been destroyed 26,000 years ago? Causing mankind to effectively start over? Is this what we can expect from 2012? If someone told you when you were going to die, would you believe them? If so, what would you do about it? Have the Mayans given us just such a warning?

Why does the calendar stop, so conclusively? Apparently, that Mayan calendar seems designed to accommodate and usher in 2012. Some are speculating a devastating and transformative pole shift with drastic climate change, others expect instead a more constructive shift in paradigm, or both or neither. Perhaps destruction leads to construction. Astronomers present a possibility that the effects of precession will alter magnetic polarity of the sun, combined with gravitational forces from the simultaneous alignment of other planets, might cause massive solar flares, and maybe could move the axis of the Earth. Nevermind whatever energies or transmissions are released upon us by aligning also with galactic center. Mayan prophecy claims that, in this period, we will experience a realignment that synchronizes us with the cycles of nature, mutating us and accelerating our evolution.

The Buddha is said to have initiated/predicted the Wheel of Dharma to turn every 500 years, for five turns... the fifth revolution having supposedly occurred in 2000, in close enough proximity to effect/initialize 2012, which also happens to be the Year of the Dragon (of serpent imagery, emblematic of wisdom, daring and change).
Something else I discovered is that the I Ching is a type of calendar system; The Book of Changes, with its 64 hexagrams, concerns the progression of time. The Yin and Yang symbol reflects the yearly cycle, with Yin/black as the female/lunar and Yang/white as the male/solar. The trigrams that compose the hexagrams are extensions of Yin (broken line) and Yang (solid line), depicting a process of balance and unification. 64 outcomes times 6 lines each equals 384, indicating a 13 month lunar cycle.

Using a computer program assigning a date to each of the 64 possibilities, starting with when the I Ching was created, philosopher/ethno-botanist Terrence McKenna realized that it corresponded to a pattern he describes and illustrates as a "time wave", which ends- independently and ignorantly of the Mayans- on 12.21.12.
There seems to be an almost binary nature and mathematical symmetry to it.
Implications of all these "coincidences" are stunning; the meme is too persistent, common and substantial to ignore or dismiss as meaningless or accidental.
Astrology and astronomy are not mutually exclusive, and ancient "primitive" cultures more in tune with nature understood this, as they monitored the position of stars in relation to natural planetary rhythms and cycles in order to plan their lives within these patterns.

For them, there was no distinction- astrology was astronomy, and no separation between Man and nature existed. Just as the location of the sun and moon and other planets effect the status and behavior of the planet, so they likewise effect people in both direct and subtle ways. It isn't necessarily so much the stars that influence people, but their relative placement in the sky at various times of the year.
Over the last decade, a collective sense of anticipation, anxiety and apprehension of some great cosmic change approaching seems to infuse the psychology of the general populace. We see it abundantly in the New Age literature and Liberal sociology, in the reactions to potential end times for 2000 and 2012. Like animals perceiving a climatic change indicating rain or earthquake, we feel a subconscious vibration suggesting something on the horizon. Something is about to happen; we don't know exactly what, or how, but maybe we know when. In the Samurai code of Hagakure, the end is important in all things.
Although, we should keep in mind- and would be wise to, that endings are also beginnings.

When one door closes, another opens.
To the Mayan culture, life and death were intrinsically and intimately connected. For them, as with Nietzsche, Buddhists and the Samurai, to die well is to have lived well. In other words, gracefully and gratefully. A New World Order is perched on the horizon.