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Imagine that these 100 pennies

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represent the total energy input from the sun to Earth.

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That energy fluctuates over time. 

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For a long time, scientists have known 

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that the sun’s energy changes in a fairly regular “solar cycle”.

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The period from minimum to maximum

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and back to minimum is about eleven years,

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but even with those cycles, there’s very limited variation in total energy output.

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These are solar energy measurements collected by a variety of missions over the years.

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The question, however, is precisely—

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—precisely—

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—how much does the sun’s energy output change?

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Experts think the number is pretty small:

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perhaps just one tenth of one percent… 

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…a tenth of a penny.

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But one tenth of one percent from the sun can have a profound influence on Earth. 

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In terms of climate change research, scientists need to understand 

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the balance between energy coming in from the Sun

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and energy radiating out from Earth, as modulated by Earth’s surface and atmosphere.  

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That’s why NASA is launching TSIS, 

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the Total and Spectral Solar Irradiance Sensor. 

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An accurate solar energy measurement

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enables other influences on Earth’s energy balance

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to be isolated and more accurately quantified. 

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That will pay big dividends 

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in terms of understanding human and natural influences on Earth’s climate.