In Astrophysics of the sun, the sun completed their own cycle in 22 years and every 11 years dia punya magnetic field of the sun will change their own polarity. and this polarity will affect the activities of the sun such as sun storm and stream of jet and as such.. and lots of scientist in the UK aspect the dooms day is because the sun itself.
for 2012 theory, i really gave a respect since that movie really go deep into astrophysics world. yep in 2012 the magnetic field of the sun will change. but we still do not know yet either the sun is quiet or noisy. it all depends on the Butterfly Effect of the sun. anyway in couple of last era man still can survive when the sun is very quite until the equator's temperature drops to around 8 degrees so I think for this time sun's cycle, it will just make a disturbance to the sun's weather that will affect our weather but not until it will make earth to be crust. mostly it will affect our communication system since lots of plasma and ions in the sun's flare meet up with sea of charge in Van Allens Belt
