Friday, April 25, 2014

Kid's Astronomy: The Sun and Other Stars Part 1

 We all know that the closest star is the sun, but what is the sun's name?  It's Sol, as in the solar system!

What does our star do for us?  It provides most of the energy on the earth!  Heat and light are obvious, of course, as is solar energy, but really, almost everything is solar energy.

The energy our bodies use to stay alive comes from the sun via plants (and the animals that eat plants).

The energy in the gas that powers our cars comes from ancient plants, and so does the coal that powers our electric plants.

Even wind energy comes mostly from the heat from the sun causing changes in our atmosphere.  Really, only nuclear energy and geothermal energy create energy that does not come from the sun - even tides are partially caused by the sun!

But where does the sun get it's energy?  To answer that, we had to look at how stars are formed.  I used the kid model.

We started out with kids scattered across the yard the way dust and gas are scattered in a nebula.  As the kids moved around, whenever they touched, they stuck together.  As the clump of kids got bigger, they were able to pull more and more kids in.

To no one's surprise, as the mass of kids got larger and larger, the kids in the middle started getting more and more squished.  I took two little girls of equal size and squished them together until.. POOF!  They turned into Mxyl!!  (OK, actually, they ducked out of the way and a previously unnoticed Mxyl popped up in the huddle).

This is very much like hydrogen getting squished into helium: it not only changes size, it changes it's characteristics into a whole new element!  The interesting thing is that the mass of the girls did not equal the mass of Mxyl: where did the extra mass go?

Sure, everyone knows it now.
You've heard of  e=mc2, right?  That extra tiny bit of mass is released as energy.  Energy that is equal to that tiny mass, times the speed of light squared.  Everyone knows that.

Except most people don't realize that when you square the speed of light, that number is fantastically high - like 35 billion!  A little mass makes a lot of energy!

And the sun actually converts 4 million tons of it's own mass into energy every second!

We only receive a tiny fraction of that energy here on earth, of course.  And we don't have to worry about the sun losing too much mass, either.
 We are in the sun's main sequence, the main part of a star's life which it spends fusing hydrogen into helium.  The sun has been doing this for 4.5 billion years, and is expected to continue for another 5.4 billion years.

After that, the hydrogen will be used up, and the sun will fuse helium into carbon and oxygen.  I asked the older kids: carbon and oxygen, where have we heard that before?

Us!  We're made out of stars!  Yep.

Now the sun, while fusing helium, will expand into a red giant, and by "expand" we mean it's size will encompass earth's current orbit.  (Not to worry, humans will be gone from the planet one way or another by then!)

 Then the sun will throw off a great deal of it's mass into a planetary nebula.  The rest will remain as a white dwarf until it burns out.

That's all because the sun is a small star. If it were a BIG star, that's another story!

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