How do you read at night?  How do you find your way through a dark forest?  How do you look nice for a camera?  You need light!  You need power!  You need to smile so the flash shines on your teeth!  Where does all of this light come from?  I can tell you in one word: the sun (okay, two words if you count "the").  The sun gives us every bit of light, every little spark, and every bit of heat that you have ever seen or felt.  We have just captured some of it to use when and where we would like.  The sun powers everything.  It's like the Earth's battery. 

The sun; nature's solar power.

You may squint to see the numbers on an electric clock.  You may blink when a camera flashes in your eyes.  Everything has a different brightness.  Luminosity is how much brightness something puts out.  It can be very little, like your shiny teeth, or it can be a lot, like an exploding star.  When the moon shines, it reflects some of the light that hits it.  The same thing happens when little bits of light shoot from your teeth to the eyes of someone else.  Light can come from a source like a match or lamp, while other light bounces off of the outside of something, like your nice teeth.


The sun is far more than a warm feeling on your shoulders or something pretty to paint in a picture.  Even though it's very, very far away, it pours down on Earth like electricity through a wire or orange juice into a glass.  Energy output is how much energy something puts out.  A table does not put out a lot of energy, but a flashlight will put out a lot more.  Since the sun runs everything on Earth, from an ant marching to the wind blowing to your eyes blinking, it has to put out a lot of energy.

Watch out, you'll run down your battery.

Everything around you takes in energy from the sun.  Your skin takes it in to make vitamin D.  Those plants take it in so they can make sugar.  That puppy is taking it in so she can get warm.  That man over there takes it in so he can get a great tan.  Joules are a measurement of energy and you can think of them like this: it takes about one joule to lift an apple 3 feet.  We can also use joules to measure how much the sun is sending down to us at any second.  This is hard to understand, but a joule is a way to tell .  We can use it to measure heat or how hard it would be to move something.  This is like trying to figure out how many grains of rice you would need to eat in order to lift that puppy . . . or the man with the killer tan.

I am sure you have heard of miles.  They measure how far away something is.  I am also sure you've heard of miles an hour.  That's how far something goes in one hour.  We use that to tell how fast something goes in an hour.  There are ways to tell how much heat something lets out.  Joules per second is how we can measure how much energy is let out by something every second.  A candle will only let out 40 joules per second, but a bright lamp will let out 120.  Every day, a part of the ground one square meter (about the size of a table) is hit with 29.4 million joules from the sun!  No wonder people skip around when it's sunny out.  They are getting their batteries charged!

You won't light the earth with this!
Photo by Toni Grappa

The sun does a lot of work on Earth.  Scratch that.  It does all of the work!  Every flash, every light, every glow, every bit of energy and heat all come from that big yellow battery in the sky.  By shining down on us, it covers everything in the energy we need to live and move.  This does not mean you should leave your toys out in the sun to catch its power.  The sun might just melt them instead.


How Stuff Works.  "Joule"  Discovery, 2011.  <>

Geography 4 Kids.  "Radiant Energy From the Sun"  Geography 4 Kids, 2008.  <>