Words can be so confusing, well for some of us at least. I even confuse myself occasionally trying to explain certain things. You can therefore imagine my trepidation when it comes to interpreting what others are saying about a strange event like “crossing the centre of the galaxy in December 2012”. This one has come up a few times recently as we head towards the “END” of the world this December 21st, so I thought I’d have my say to try and explain what is going on.

Rest assured the world will not end this year or anytime soon. Nonetheless we appear to cross the plane of the galaxy this December, as we see it. In fact we do it twice a year at the winter and summer solstice because of the Earth’s tilt on its axis, which incidentally also causes the seasons. This is however a purely visual effect as our entire Solar System is presently something like 75-100 light years above the plane of the galaxy.

It gets worse. Yes we do pass through the plane in a complicated gravitational dance that takes about 33 million years to complete one cycle of above and below. We last crossed the plane roughly 3 million years ago and are not expected to do so again for another 30 million years, certainly not in 8 months’ time.

Will we ever really pass through the centre of the galaxy? No, and I can say with absolute confidence that is never going to happen. The Milky Way galaxy is very large at about 100,000 light years side to side. Our small solar system is about 28,000 light years from the massive black hole that lurks at the centre. We won’t ever go through the centre but we do “fall around” or orbit the centre of the galaxy about once every 250 million years.

In summary, this December like all Decembers we will appear to cross the plane of the galaxy as we see it, but we will really cross only in 30 million years’ time and we will never pass through its centre.