John Major Jenkin's Insight on the astronomy Behind The Maya Calendar End Date

As near as I can make out from the information that John Major Jenkins shared in his book Cosmogenesis 2012 the mechanics via which the now famous Winter Solstice galactic alignment manifests in the year 2012 work like this: The earth makes an orbital circuit around the sun approximately every 365 days. Because the earth's axis is tilted, at some times during that annual circuit the northern hemisphere where I live and also where the ancient Mesoamericans have always lived is inclined toward the sun and receives the sun's rays directly creating the summer season. However by the same token at other times of the circuit the northern hemisphere that I share with the Mesoamericans tilts away from the sun creating the Winter season. That's a constant. That never changes.

What does change is that the tilt of the earth's axis does not stay the same all the time. It changes very slowly marking a conical circuit that makes the earth look like its wobbling gradually. This wobble is circular, very much like the wobble of a spinning top but also so very, very slow that it takes the earth roughly 26000 years to complete one wobble. During that whole time the earh continues on its merry way spinning around the sun every 365 days but over the span of centuries its tilt in relation to the sun and in relation to everything else around it shifts gradually. This 26000-year phenomenon is called "Precession".

The earth lines up with the sun in such a way as to align with the Milky Way Galaxy once a year no matter what. But this alignment can take place at any given point and at any given season during its annual rotation around the sun depending on the way it happens to be tilted at a given time in its 26000-year precessionary cycle. At a period of history about two hundred years B.C. The alignment of the earth-sun-Galaxy did not take place during winter solstice. It took place at another time of the year. However, as Jenkins has demonstrated, the people living at that time in the ancient community of southern Mexico called Izapa (precursors of the classic era Maya) came to the conclusion that this state of affairs was not permanent and that eventually, some time in the distant future, the alignment would take place on the Winter Solstice. As Jenkins has suggested, this excited them because the Winter Solstice was a time that was seen as a kind of sacred beginning, a "birthing time. The bright, thick central bulge of the Milky Way Galaxy's core represented a metaphoric image of cosmic pregnancy to the early Mesoamericans. If the sun and the galactic plane close to the galactic core were to someday align on Winter Solstice (especially if it happened near a unique dark structure called the "Dark Rift" located at that site which the ancients identified as a kind of dark birth canal) it would be considered a wonderful event literally pregnant with possibility for humanity. They understood that they themselves were not going to witness this marvelous event but they predicted it into the distant future, over two thousand years forward, and went to great pains to record the result of their astronomical research in the form of hieroglyphic inscriptions so that those who came after them would understand what they had discovered. These inscriptions are the ones Jenkins indicates in his books and videos as he walks us through the ruins of that ancient site.

They may not have fully understood the mechanics of the earth's tilt that made this astronomical possibility real but they did know how to use their advanced mathematics to figure out when this Winter Solstice alignment was going to take place, around the year 2012. according to Jenkins they got busy building an elaborate mythological complex around this fact and created the Long Count system to accurately measure how long it takes for this winter solstice sun-earth-galactic plane alignment to repeat. They came up with a cycle of a little under 26000 years divided into five smaller periods of almost 5200-years each, sometimes called the five "suns" or five "world ages". Western astronomers also arrived at a similar measurement of the roughly 26000-year-long precessionary cycle and called it the "Great Year".
I will include two graphic images that I created on the Windows utility "paint" to illustrate how the tilt of the earth changes over long periods of time and how that change affects Precession.

The first image below shows the earth at the point in its 26000-year wobble as it was around the time of the ancient Izapans. You will notice that during that era on the Winter Solstice location in its annual journey around the sun the earth and the sun are NOT lined up with the galactic plane.
The second image shows the point to which the earth's tilt has progressed as a result of two thousand years of precession, now around the year 2012. As you can see at this period of history the earth, the sun and the plane of the Milky Way Galaxy DO line up on the Winter Solstice during this present era just as Jenkins asserts that the ancient Izapans predicted.
Please click on the pictures to enlarge them and get a good detailed look at them.