Tuesday, April 15, 2014

Kids' Astronomy: The Moon

We started out outside, asking questions: what is the moon?  Lots of great answers from the kids: everybody knew about the moon.

All right then, what's it's name?  Ummmm... "The Moon."

Except that's not the moon's name.  It's really called Luna.  I explained that, many years ago, people thought that if you slept in the light of a full moon, you would become a...lunatic!

We played a few rounds of "Full Moon, New Moon," a completely made up game in which they acted calm and reasonable when I said "New Moon," and like lunatics when I called, "Full Moon."

Then I asked them to draw the shape of the moon with sidewalk chalk.  I got a pleasing variety of moon like shapes from the traditional crescent, to circular full.  I explained that they were all correct, and we went in to the basement to see how the moon appeared to change shape.

Before I jumped into the phases, however, I did a skit.  Who Has Moons?  I played the nosy investigating reporter, and my lab assistants portrayed the planets.

Me: So, got any moons?

Mercury: Nope, too close to the sun.

Venus: Not me, I'm too close to the sun.

Earth: Sure, I've got a big one!

Me: What!  You shouldn't have a moon!  You're too close to the sun!  I'll get back to you.

Mars: I've got two moons.

Me: You shouldn't have any either - you're too close to the sun... Wait a minute, you've got little lumpy potato  moons... they look like asteroids!  You stole these from the asteroid belt!  Admit it! 

Mars: Well, they're my moons now!

Jupiter: Oh, I've got dozens of moons: more than 60.  Too many to bother counting, really...

In fact, all the gas giants have dozens of moons.  That's because they aren't too close to the sun - their own gravity was enough to form the moons along with the planet.  So, why does the Earth have a moon?

The favorite theory is that a planet the size of Mars collided with the Earth, early enough in the formation of the solar system that the Earth was still molten.

Enough combined material from Earth and the other planet (Theia) was thrown off that it coalesced into the moon.

On to the moon phases!  I've done this many times before, but this was the best model I've used: the "moon" was a ball of pale yellow yarn with a knitting needle stuck through so that it could be held without obscuring any of the phases.

I used a flashlight aimed directly at the ball as the sun.  I had the kids (in small groups stand in the middle as the Earth, and look at the ball as it traveled around them. Moon phases!

When it was in front of the sun, they couldn't see any of the ball lit up: new moon.  When it was behind the Earth, the entire ball was lit up: full moon.  In the in between places, they  saw the rest of the phases moving from new to full and back to new.

While we were at it, I showed them the lunar and solar eclipses on one of my lab assistants!  You could see the shadow of our "moon" on his shirt as it passed in front of the flash light, and you could see the "moon" pass into his shadow for the lunar eclipse.

Then we went outside to look at the sun (cast through a pin hole and projected on white paper, the best way to see an eclipse).
Naturally, the sun appeared as a round dot, and it's easy to think that is because the pin hole was round.

Then I showed them some photographs taken during an eclipse in Madrid.  What you are seeing is the dappled light through a tree.  But all the dapples are eclipsed!

We talked about tides next.  I have been looking for a good model of how tides work, and this is an adaptation of Explain-It's tide model.

The little globe is the Earth and the clay ball is the moon.  The blue circle is the Earth's water (actually some stretched out lanyard plastic rope).  You could use a file sized rubber band, but it helps to have some stiffness - plain string might be tricky.

You move the moon around, pulling on the water, showing that some of the water stays in a bulge behind the Earth, shielded from the moon's pull. The two bulges (one towards the moon and one behind the Earth) are the high tides,  The narrower places to the sides are the low tides.

You can also show how, if the sun and moon line up, you get higher tides, and when the sun is pulling on the lower narrower sides, you get lower (neap)tides.

Next we talked about why we liked the moon (beauty, tides, light at night, made of cheese, etc.).  You know someone had to say it was made of cheese.

But, did you know that the moon is white for the same reason cheese is (more or less) white? Calcium compounds.

I told the kids that I like the moon because it's slowing down the earth- otherwise our day would be 6 hours and we would have very different weather from the faster spin!

I also like it because it stabilizes the tilt of our axis so we have milder, more stable seasons.

And, of course, it does take at least some of the meteors that would have hit Earth.

We did a crater experiment, dropping rocks into two inches of flour covered with a dusting of coca powder.

They tried different sizes of rocks, and dropping them from different distances.  The lab assistants got to try dropping several at once in a "meteor storm!"
Lastly, we talked about what it was like on the moon: cold/hot, rocky/dusty, airless, and, best of all, low gravity!

I had them jump as far as they could on the driveway.  Then I multiplied that distance by 6 and marked out how far they would have gone on the moon!

Our smallest jumper would have gone 24 feet!

Our largest jumper would have been past the driveway, past the street and well into the neighbor's yard - 65 feet!

A big thank you to all my flashlight-shining-little kid-carrying-ball-orbitting-planet-impersonating-rock-dropping-moon-jumping-photo-documenting lab assistants!

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