There are a number of aspect to your question so I hope that this
research should be able to separate them and inform you as to how the
earth is possibly affected by its journey through the galaxy.
Our sun is part of a large mass of stars, interstellar gas and dust,
and possibly dark matter. This is known as a galaxy. Ours we call the
Milky Way. The Sun orbits the centre of the Milky Way at a distance of
about 25,000 to 28,000 light-years from the centre, and it takes about
226 million years to complete a revolution. This graphic shows in a
simplistic way the shape of the galaxy and the sun?s position in the
This photograph is a side on view of a similar galaxy.
You can read more about different galaxy shapes here.
?Our own galaxy, the Milky Way, sometimes simply called the Galaxy
(with uppercase), is a large disk-shaped barred spiral galaxy about 30
kiloparsecs or 100,000 light years in diameter and 3,000 light years
in thickness. It contains about 3x1011 stars and has a total mass of
about 6x1011 times the mass of the Sun.?
Viewing the galaxy from the side, astronomers draw an imaginary line
along length of it called the ?plane of the galaxy? or ?galactic
plane?. The line is used as a co-ordination system for astronomers.
See this for additional information.
During its journey around the galaxy, the sun wobbles above and below
the galactic plane. This is how one theorist describes it, ?so the
Solar System bobs up and down like a horse on a carrousel through the
dense, central portion of the galactic disk? (Michael Rampino - see
As the quote mentions, the central part of the disc is the densest
part of the galaxy and it is the existence of the dense area and the
sun?s journey through it which has given rise to theories that this
may explain life extinction events on earth.
Before moving to these theories you may wish to view the information
and pictures on the below links to give you some additional background
information. These links are to Canadian Galactic Plane Survey which
is part of a project to map to the interstellar matter of the Milky
As this web site notes, scientists are still undecided on the exact
size and shape of the galaxy and the suns? position in the galaxy, and
exact measurements are problematic.
?The structure of our galaxy is hard to determine from the inside,
especially because distances are often difficult to measure in
astronomy. The situation is somewhat analogous to maps of the Earth in
the early days of cartography.?
This article from American Scientist I would also recommend reading.
?The Galactic Environment of the Sun?.
The article tells us that this up and down movement of the earth means
that the earth crosses the plane every 33 years. Other sources
referred to below, give a figure of 27 - 36 million years, so we see
here an example of the difficulties involved in astronomical
?The sun's path is inclined about 25 degrees to the plane of the
galaxy and is headed toward a region in the constellation of Hercules
near its border with Lyra. The sun oscillates through the plane of the
galaxy with an amplitude of about 230 light-years, crossing the plane
every 33 million years.?
The various extinction events which have occurred during the world?s
history have attracted a number explanations. One such hypothesis is
that these events coincided with the earth crossing the galactic plane
and encountering the dense matter in the form of comets which struck
the earth. This is known as the Shiva Hypotheisis. Its author is
Michael Rampino, Associate Professor of Earth and Environmental
The citation is:
Rampino, M. R. and Haggerty, B. M. (1996) The "Shiva Hypothesis":
impacts, mass extinctions and the galaxy. Earth, Moon & Planets
A summary of the Shiva Hypotheisis written by Rampino appears here.
This is another summary.
Rampino, M.R., and B.M. Haggerty 1996. The "Shiva Hypothesis":
Impacts, mass extinctions, and the galaxy. Earth, Moon, and Planets
?The mass extinction record shows evidence for a periodic component of
about 26 to 30 Myr, and an ~30 Myr periodic component has been
detected in impact craters by some workers, with recent pulses of
impacts in the last 2-3 million years, and at ~35, 65, and 95 million
years ago. A cyclical astronomical pacemaker for such pulses of
impacts may involve the motions of the Earth through the Milky Way
Galaxy. As the Solar System revolves around the galactic center, it
also oscillates up and down through the plane of the disk-shaped
galaxy with a half-cycle ~30±3 Myr. This cycle should lead to
quasi-periodic encounters with interstellar clouds, and periodic
rotations in the galactic tidal force with maxima at times of plane
crossing. This "galactic carousel" effect may provide a viable
perturber of the Oort Cloud comets, producing showers of comets in the
inner Solar System. These impact pulses, along with stochastic
impactors, may represent the major punctuations in earth history. ?
This page carries a diagram and some other information on periodic
?One hypothesis is that this corresponds the the solar system
oscillating through the galactic plane as it orbits the Milky Way.
Rampino notes that the last crossing of the galactic plane occurred a
few million years ago and it has been suggested that this led to a
disturbance of comets in the Oort Cloud, some of which could now be
approaching the inner solar system.?
Other scientists have followed up on this work and have made the
?The Sun's motion perpendicular to the galactic plane
John N. Bahcall* & Safi Bahcall?
For all the models we consider, the most recent passage of the Sun
through the galactic plane occurred in the past 3 Myr provided only
that the present position of the Sun is between 0 and 20 pc above the
plane. We extend the argument of Thaddeus and Chanan8 to show that the
apparent periodicity in the mass extinction and cratering records
cannot be caused by an population of objects (observed or unobserved)
that contributes a major fraction of the total mass density at the
?We find this terrestrial cycle to be strongly correlated with the
time needed for the Solar System to oscillate vertically about the
plane of the Galaxy, which is 33 plusminus 3 Myr according to the best
current astronomical evidence.?
Large Meteorite Impacts and Planetary Evolution II
p242 ?the sun?s last crossing of the galactic plane occurred in the
last million years or so?
In these and other sources it is suggested that earth crossed the
galactic plane within the past 3 millions years (depending on which
model or measurements are used). So how does the year 2012 come into
the equation? As far as I can establish this date comes from a theory
that the Mayan?s calendar was due for renewal in 2012. One particular
writer, John Major Jenkins, has written that this coincides with the
crossing of the galactic plane and the aligning of earth?s solar
plane. I have not read them in any detail and may have simplified it.
You can read of his theories on these links.
THE HOW AND WHY OF THE MAYAN END DATE IN 2012 A.D. by John Major Jenkins
Galactic Alignment: The Transformation of Consciousness According to
Mayan, Egyptian, and Vedic Traditions (Paperback) by John Major
Other references to 2012 may be found in the search term at the
bottom. Some of theories are confusing and most of them appear
apocalyptic. For instance, in Answers for Everything by Joe Paladin,
p85, of the Mayan Prophecy he writes that 2012 will bring the end of
the world as crossing the galactic plane will change the
In conclusion, I should obviously state that the Shiva Hypothesis is
only a theory and is open to debate and challenge.
I hope this answers your question. If it does not, or the answer is
unclear, then please ask for clarification of this research before
rating the answer. I shall respond to the clarification request as
soon as I receive it.
"Galactic Plane " crossing
mayan 2012 "galactic plane"
Request for Answer Clarification by
06 Oct 2005 02:32 PDT
You have provided fascinating links and clearly there are many
theories to consider; Very good synopsis of extinction events. I have
a final question. I am aware that the whole issue of a supposed
"galactic crossing in 2012" is a "byproduct" of the Mayan Calendar
literature frenzy that is proliferating these days. I was already
somewhat aware of Jenkins'ideas, and though they are complicated, they
seem to be intertwined with various mythologies, which, as you have
probably surmised in your own research, leaves out science. So,
getting back: is it possible to determine, from what the science of
astronomy has to say, if there is any "galactic significance" (for
lack of a better term) in 2012? In other words, stripping away the
Mayan Calendar speculations, is it really an "eventful" year for the
galaxy, or is this just part of the 2012 hoopla? I have just seen a
comment posted stating the crossing "cannot be pinned down to a year".
Would appreciate a check on what astronomy has to say. Thanks.