We have found an IELTS reading simulation exercises--Suns fickle heart may leave us cold.
Sun's fickle heart may leave us cold
□ 25 January 2007
□ From New Scientist Print Edition.
□ Stuart Clark
1 There's a dimmer switch inside the sun that causes its brightness to riseand fall on timescales of around 100,000 years - exactly the same period asbetween ice ages on Earth. So says a physicist who has created a computer modelof our star's core.
2 Robert Ehrlich of George Mason University in Fairfax, Virginia, modelledthe effect of temperature fluctuations in the sun's interior. According to thestandard view, the temperature of the sun's core is held constant by theopposing pressures of gravity and nuclear fusion. However, Ehrlich believed thatslight variations should be possible.
3 He took as his starting point the work of Attila Grandpierre of theKonkoly Observatory of the Hungarian Academy of Sciences. In 2005, Grandpierreand a collaborator, Gábor ágoston, calculated that magnetic fields in the sun'score could produce small instabilities in the solar plasma. These instabilitieswould induce localised oscillations in temperature.
4 Ehrlich's model shows that whilst most of these oscillations cancel eachother out, some reinforce one another and become long-lived temperaturevariations. The favoured frequencies allow the sun's core temperature tooscillate around its average temperature of 13.6 million kelvin in cycleslasting either 100,000 or 41,000 years. Ehrlich says that random interactionswithin the sun's magnetic field could flip the fluctuations from one cyclelength to the other.接下来为大家介绍"探讨雅思阅读模拟练习：Suns fickle heart may leave us cold"
雅思阅读模拟练习：Suns fickle heart may leave us cold
5 These two timescales are instantly recognisable to anyone familiar withEarth's ice ages: for the past million years, ice ages have occurred roughlyevery 100,000 years. Before that, they occurred roughly every 41,000 years.
6 Most scientists believe that the ice ages are the result of subtlechanges in Earth's orbit, known as the Milankovitch cycles. One such cycledescribes the way Earth's orbit gradually changes shape from a circle to aslight ellipse and back again roughly every 100,000 years. The theory says thisalters the amount of solar radiation that Earth receives, triggering the iceages. However, a persistent problem with this theory has been its inability toexplain why the ice ages changed frequency a million years ago.
7 "In Milankovitch, there is certainly no good idea why the frequencyshould change from one to another," says Neil Edwards, a climatologist at theOpen University in Milton Keynes, UK. Nor is the transition problem the only onethe Milankovitch theory faces. Ehrlich and other critics claim that thetemperature variations caused by Milankovitch cycles are simply not big enoughto drive ice ages.
8 However, Edwards believes the small changes in solar heating produced byMilankovitch cycles are then amplified by feedback mechanisms on Earth. Forexample, if sea ice begins to form because of a slight cooling, carbon dioxidethat would otherwise have found its way into the atmosphere as part of thecarbon cycle is locked into the ice. That weakens the greenhouse effect andEarth grows even colder.
9 According to Edwards, there is no lack of such mechanisms. "If you addtheir effects together, there is more than enough feedback to make Milankovitchwork," he says. "The problem now is identifying which mechanisms are at work."This is why scientists like Edwards are not yet ready to give up on the currenttheory. "Milankovitch cycles give us ice ages roughly when we observe them tohappen. We can calculate where we are in the cycle and compare it withobservation," he says. "I can't see any way of testing [Ehrlich's] idea to seewhere we are in the temperature oscillation."
10 Ehrlich concedes this. "If there is a way to test this theory on thesun, I can't think of one that is practical," he says. That's because variationover 41,000 to 100,000 years is too gradual to be observed. However, there maybe a way to test it in other stars: red dwarfs. Their cores are much smallerthan that of the sun, and so Ehrlich believes that the oscillation periods couldbe short enough to be observed. He has yet to calculate the precise period orthe extent of variation in brightness to be expected.
11 Nigel Weiss, a solar physicist at the University of Cambridge, is farfrom convinced. He describes Ehrlich's claims as "utterly implausible". Ehrlichcounters that Weiss's opinion is based on the standard solar model, which failsto take into account the magnetic instabilities that cause the temperaturefluctuations.
IELTS reading needs more practice.An article,Suns fickle heart may leave us cold, is not enough.We hope that the majority of candidates continue to work hard.
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