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★Suns fickle heart may leave us cold 25 January 2007 From New Scientist Print Edition. Stuart Clark 1.Theres a dimmer switch inside the sun that causes its brightness to rise and fall on timescales of around 100，000 years - exactly the same period as between ice ages on Earth.So says a physicist who has created a computer model of our stars core. 2.Robert Ehrlich of George Mason University in Fairfax， Virginia， modelled the effect of temperature fluctuations in the suns interior.According to the standard view， the temperature of the suns core is held constant by the opposing pressures of gravity and nuclear fusion.However， Ehrlich believed that slight variations should be possible. 3.He took as his starting point the work of Attila Grandpierre of the Konkoly Observatory of the Hungarian Academy of Sciences.In 2005， Grandpierre and a collaborator， Gbor goston， calculated that magnetic fields in the suns core could produce small instabilities in the solar plasma.These instabilities would induce localised oscillations in temperature. 4.Ehrlichs model shows that whilst most of these oscillations cancel each other out， some reinforce one another and become long-lived temperature variations.The favoured frequencies allow the suns core temperature to oscillate around its average temperature of 13.6 million kelvin in cycles lasting either 100，000 or 41，000 years.Ehrlich says that random interactions within the suns magnetic field could flip the fluctuations from one cycle length to the other. | 
