Kids' Astronomy: the Moon

 Just a few pictures from from our class on the moon.

I mean, we weren't actually on the moon, but, you get the idea!

Moon crater experiment: dropping rocks onto flour dusted with cocoa.

 Explaining tides: the round blue pot holder is the Earth, the black rope is the water.

Explaining moon phases with a ball of yarn stuck on a knitting needle.

 Drawing moon phases.

I love how into this kids get!






We also did the moon jump.  You mark how far the kids jump, then multiply it by 6 and mark again how far their jump would carry them on the moon!

The full class is here.

Kid's Astronomy: Planets 2

Creating Saturn's rings and shepherd moons

This was this week's class, the outer solar system.  The original of this class was blogged here, I'm just adding current pictures and noting anything I did differently.

Building the comet

Comet after sublimation

The big thing I did differently was to get extra dry ice (note to self, 5 pounds was plenty).








We put it colored water and chemistry glassware to look like mad scientists.

And we put it into juice for the kids to drink!

I also showed them why proper ventilation is needed.  I lowered a candle into the CO2 filled ice chest, then poured it from one of their bubbling flasks.

A marvelous time was had by all!

Kid's Astronomy: Sun Part 3

I almost forgot!



Or, if you prefer to be more precise:


Although, to be honest, since plasma is just an ionized gas (gas with the electrons stripped away), I prefer the first song. Mostly because it's catchier.

Kids' Astronomy: The Sun and Other Stars, Part 2

We left off with the life cycle of our middle sized star, Sol.  But what if Sol had been a large star?

For one thing, we wouldn't be here.  If you have a really massive star, planets in the "Goldilocks zone" (where you have liquid water) tend to get tidally locked so that one side of the planet always faces the sun.

For another, massive stars (with their massive gravity), squish hydrogen much faster, so they live less long. They live brighter and hotter, but shorter lives.

Incidentally, the color of the stars is directly related to their temperature.  What do you think the

blue where it's hottest

hottest color is?  Most of the kids thought, "red hot," but if you look at a candle flame, you can see this is not so.   The outermost (coolest) edge of the flame is red, the innermost (hottest) heart of the flame is blue.

And so it is with stars: the coolest stars are red - only about 3000 degrees.  Medium hot stars (like the sun) are yellow, about 6000 degrees.  The really hot stars are blue and white, and they can be 30,000 degrees!  These are all surface temperatures, of course.  The core of the star, where the fusion takes place, is much hotter.  Our sun had a core temperature of 14 million degrees!

Back to those massive stars, after their hydrogen is helium and their helium is carbon and oxygen, they can go right on squishing!  Carbon and oxygen become neon, which gets squished into magnesium, then silicon, then iron.  Then the star can't "squish" anymore.  It explodes into a supernova!

The explosion tosses off gas and dust into an interstellar nebula... Which then begins to condense into new stars.

Meanwhile, what is left of the star becomes either a neutron star or a black hole!

I don't know if you've see the wonderful You Tube going around about gravity/ black hole models, but I really wanted one!  The best I could do on my budget was to put the stretchiest material I could find over a hula hoop.  It's gathered fairly loosely with a rubber band under the hoop.

A small mass (a marble) dented the material in the same way that a small object (like a moon or a planet) bends space around itself.  A large mass, like the rock (or star), bent the fabric enough that the smaller mass would orbit around it!

So.  We have all these stars, in all these stages of the star cycle, scattered throughout the universe and clumped into galaxies.  Most of them are millions of light years away, so how do we study them?

We study their light!  With things we want to study here on earth, we put them under a microscope to see their parts.  With light from space, we use a telescope with a spectrometer.  Believe it or not, building four working spectrometers was in the budget!

You take a paper towel roll and cut a slit near one end at a 45 degree angle.  That slit is where you will put an old CD, or part of a CD (I cut mine into fourths to make four instruments).  The CD is going to spread out your light into a spectrum.  You also need to cut a rectangular viewing hole above the CD so that you can see that spectrum.

On the other side of the roll, cover the open end with foil.  Cut a slit in the foil so that it lines up with the CD.  That slit will allow a narrow beam of light into the tube and onto the CD, the CD will spread the light by wavelength, and you will view a column of separated light through the viewing hole on the top.  More detailed instructions here (HT: Aurora Lipper)

Solar spectrum from a professional!

You point the slit at the light source you are interested in.  We looked at a number of florescent lights first, because these lights only emit certain wavelengths, so you get bright bands of widely separated colors.  We looked at warm tone, cool tone, yellow, and "black" florescents, as well as an incandescent bulb (which gives a much fuller spectrum) and then, of course the sun!

Amazingly, even our home made spectrometers, we were able to see the black lines in the sun's spectrum!   These lines are the elements in the sun itself that absorb certain wavelengths of light.  Each star has a pattern of these lines which tell us exactly what it is made of!

We finished up with a brief discussion of constellations.  I showed them some flashlight constellations (you put foil over the flashlight, prick the pattern of holes in it, then shine it on the ceiling), how to use a star chart, and lastly, the constellation illusion.

Not so lined up!

Essentially, the only place the constellations exist is on earth.  At other points in the universe, the stars just don't line up that way.  I used my lab assistants as the stars and had them line up as a straight line "constellation."  This is how the constellations look to us: as if the stars are lined up at the same distance.

Then I moved my assistants so that they were at varying distances.  From one spot, they still looked like they were all in a straight line, but from every other vantage, they were in a different pattern.

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!

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!

Kids Astronomy: Planets Part 2

Moving out into the outer solar system, we come to Jupiter, king of the planets. What do you get when you add very massive planet plus close to an asteroid belt?  In this case, 62 moons!

At at 100 times the size of Earth, you would think a Jovian day would be very long. Nope.  A day on Jupiter lasts a mere 10 hours.

That super fast spin generates incredible winds and super storms, like the Great Red Spot, a hurricane that is larger than the entire Earth and has been going on for at least 400 years.

Choclo is using our tornado tube with orange water and red glitter to demonstrate the storm.

 All the gas giants have rings, but none are as well known as Saturn's.  I used more powder and salt to demonstrate the dust and ice which form those rings.  I then had a lab assistant drag pencils (eraser side down) across it to show how Saturn's moons "shepherd" the rings into distinct sections.

As a kid, I was told that the gas giants had no surface below all that atmosphere, that they were gas all the way through.  This made no sense to me.  Wouldn't the mass of the planet crush the gas into a solid, or at least a liquid?

The actual answer seems to be yes, at least for Jupiter and Saturn.  But there is still no "surface." It is now believed that the gases are compressed so gradually, that there is no definite point where the atmosphere stops being gas and starts being liquid.

 Next up, the mysterious (and hard to pronounce) Uranus.  Firstly, we don't know why it spins on it's side, but it gives it really strange seasons.

We used the globe and flashlight trick again, and it's worth ding just to see this for yourself.

During winter, half of the entire planet gets no sun for 21 years. During summer (21 years) the sun does not set.  In spring and fall, they get something more like our days and nights.

Weirder than that, scientists think there is a surface under Uranus's atmosphere.  One theory is that the surface is very cold and covered with large diamonds.  Another theory holds that the surface is a very hot (5000 degree) ocean.

So, anyone want to go and find out?

That leaves Neptune as the last of the true planets.  It's like Uranus, only smaller, and with faster winds.  Neptune has a large, long lasting hurricane called The Great Dark Spot, and a white cloud (very helpful when measuring rotation) which astronomers call "Scooter" for the speed with which it scoots around the planet.

What about Pluto?  Two interesting things about our distant dwarf planet.

Did you know that they keep finding new moons of Pluto? Right now it's up to four, with a possible fifth awaiting verification. Not bad considering Pluto is much smaller than our own moon!

Also, its one of many Kuiper belt object (also called Trans Neptuniam Objects).

The Kuiper belt is like a second asteroid belt after Neptune, except the "asteroids" are larger, farther apart, and their orbits are a little bit tilted from the rest of the planets' orbits.

Past the Kuiper belt, you have the Oort cloud.  This is  a remenant  of the cloud of dust and gas the solar system formed from, and it is the very outer fringe of the solar system.

It's so far away from the sun, that the sun's gravity holds objects here very weakly.  Any passing object can affect trajectories here, sometimes sending chunks of ice and dust spinning towards the inner solar system.

We call these comets!  And here is how to make one.

Line a bowl with a trash bag.
Pour in 2 cups of water.
Add a few spoons of sand or dirt.
Add a splash of ammonia.
Add some simple sugars (dark corn syrup or molasses)
Stir, then add 1 cups of crushed dry ice.
Wearing gloves (!) form the freezing mess into a snowball by pressing on the outside of the trash bag.



Dump it out, and there you have it!

Of course, to be a real comet, you'd have to shoot it into space, but if you'd rather keep it here, you can make your own "solar wind" by blowing on it.  The dry ice generates a fine "tail" and the whole "dirty snowball" eventually disintegrates into a lacy ball of ice in very much the way a real comet does.

Kid's Astronomy: Planets Part 1

Can you name the planets?  Do you consider Pluto a planet?  What is a planet, anyway?

The planets all go around the sun, of course, but so do plenty of things that aren't planets (asteroids and comets, for example).

The planets are all more or less round: they have enough mass to draw themselves into a rough sphere.  But there are large asteroids and dwarf planets that do that.

A true planet is large (massive) enough that it's gravity has cleared all the space around it.

That means we know of 8 planets and 11 dwarf planets.  Oops, they found another dwarf planet yesterday!  So that makes 12 dwarves, so far!

So, more or less round?  Aren't the planets ball shaped?  Actually, most of them are a little squashed from spinning.  The faster the spin, the more they bulge at the equator.  It's really noticeable with Saturn!

Here's an easy way to see why this happens: Cut out two long thin strips of construction paper and punch holes on both ends.

Thread the holes onto a pencil so that you form a ball with the pencil just inserted a little way into the ball (we stapled the part where the strips cross to give some stability).

When you twirl the pencil, the ball flattens from the centrifugal force, just like the planets!

But even the true planets aren't very similar.  Some are small and rocky, and some are huge and made of gas.  Ever wonder why?  And why are the close ones rocky, and the gas ones far away?

We think it has to do with the way the solar system was formed.  The sun formed from a cloud of dust and gas: as bits bumped into each other and stuck, the gravitational pull increased, sucking more and more of the cloud into a central location and starting things spinning.

When the sun grew large enough to ignite (more on this in another class) it began in spurts that blew bursts of solar wind like explosions across the solar system.  Lighter gases were blown farther out, heavier elements stayed closer to the center.  Meanwhile, at the fringes, bits of dust and gas that hadn't been drawn near yet, stayed the same.

You can see this if you take a black trash bag and lay it flat.  Mix together talcum powder to represent the lighter gases and a bit of salt to be the heavier rocky elements.  Drop the mixture onto a corner of the trash bag while you (or a bunch of kids!) blow.  You'll find powder clear across the bag, but most of the salt will stay close to where you dropped it.

And, of course, you can see it in the solar system with the near rocky planets, the distant gas planets, and the far icy and rocky Kuiper belt dwarf planets.

First up, we looked at Mercury: so small, so rocky, so hot (800 facing the sun), so cold (-300 facing space), and so fast (zipping around in it's 88 day year)!   To look at why the close planets have such short years, I took a long stick with a knob at one end, and a knitting needle with a ball at the end.  I stood them side by side, ball side up, and then let them fall to the ground.  The larger stick moved faster, but the shorter needle took less time: it was covering less distance.

Then we looked at Venus: 900 degrees - hotter than Mercury - how can that be?  Earth and Venus started out not only the same size, but also containing the same proportions of elements.  The two were nearly identical!  But Venus was too close to the sun.  That extra heat developed a thick carbon dioxide atmosphere that held in heat and created clouds of sulfuric acid.  There's a reason we send rovers to Mars, not Venus!

I had set a pair of identical ceramic tiles in a 300 degree oven half an hour before the class.  At the beginning of the class, I took them out and covered one with a wool blanket to simulate Venus's insulating atmosphere.  Now, 20 minutes later, I removed the blanket and took the temperature of each tile with a scanning thermometer.  The covered tile was 140, the uncovered 100.


Next up, we have Earth, the Goldilocks planet!  Not too hot, not too cold, juuuust right for liquid water.

 I took the kids downstairs, turned out the lights, and showed them the seasons on our globe using a flashlight.  When our part of the Earth is tilted towards the sun, we have summer.  When it's tilted away, we have winter.

I have found that most kids think that the Earth is closer to the sun in summer.  Here in the Northern hemisphere, in the summer the Earth is actually at its furthest point away from the sun (and in our winter, the Earth is closest to the sun).  The opposite is true for the Southern hemisphere, which is why their seasons, all else equal, are slightly more extreme.  The 23 degree tilt towards or away from the sun is really what makes the difference.

The last of the inner planets, Mars is only half the size of Earth.  Too cold, too small to hold a good atmosphere, most of the surface water has evaporated.  It's a dead planet in the largest sense: it's core has cooled and solidified.

It no longer has volcanoes, moving tectonic plates, or, critically, a magnetic field.  Earth has a magnetic field because our core is liquid and moving as the planet spins.  That field shields us from all sorts of solar and cosmic radiation which would otherwise wipe out life on the surface of the planet.

My "Mars" rock isn't from Mars, it's common iron stone that we found on a fossil expedition, but it's similar to the iron rich rocks which give "The Red Planet" it's color (and weirdly enough eroded to look alien!

Absolutely NOT!

Last for today: the asteroid belt.  When I was a kid, it was thought that the asteroids could be the remains of a destroyed planet.  Now astronomers think it is debris that didn't have enough mass to coalesce, thanks in part to the pull of Jupiter.

One thing they always agreed on: remember the asteroid belt in Star Wars?

That is absolutely NOT what an asteroid belt looks like!  If there were that many rocks, you'd have a planet there.  In real life, standing on an asteroid in the densest part of the belt, you would not be able to see any other asteroids.

The total mass of all the asteroids is estimated to be about 4% of the mass of our moon.

Stay tuned, tomorrow I'll post the rest of the solar system!