tt_icon_170In this week’s episode of Science Teaching Tips, we look at my favorite thing — light.  Light, like, rulez.  Dude.  And so does my old mentor, Paul Doherty, who will tell you one of his best stories from the history of science about how the spectrum came to be the spectrum.  I mean, what the heck is indigo anyway?  The answer turns out to be, like all good history of science stories, steeped in mysticism and superstition.   Give it a listen, it’s a good story!

Episode 65:  Revising the Rainbow.


I’m surprised at the number of people who haven’t seen this one, but then again, neither had I until I went to the Exploratorium (where they’ll stick anything in a microwave).

Put a bar of Ivory Soap (no substitutes!) on a paper towel in the middle of the microwave.  Press go.  About 2 minutes should do it.  Here’s what happens:

And this video will show you what it looks like when you take it out afterwards

What’s going on?  Well, the reason that Ivory Soap floats (try it) is that it’s puffed full of air (here’s some history of why that is).  There are tons of tiny bubbles whipped into it, sort of like when you make whipped cream.  It’s an emulsion of soap and air.  The bubbles of air have water vapor in it.  When you microwave it, that water vapor creates pressure on the air bubbles making them expand and puff up.  The air bubbles themselves expand as they heat since the volume of a gas increases with temperature (Charles’ Law).  And the soap softens, which allows the whole thing to expand into a big puffy pile.  And when you stop heating it?  The soap’s no longer soft, so it gets rigid and hard, but stays its expanded puffy self.  You can use it like soap now, though it’ll be a little weird!

Other brands of soap tend to just melt.

Here’s a nice explanation, as well as how to use this as a classroom lesson on density, from Steve Spangler Science.  And some more classroom suggestions from

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Here’s what you do — slice a grape in half, but keep the halves connected by a little “hinge” of grape skin.  Some suggest drying off the grape halves a little.  Some suggest using a green grape in particular, and some say to cut it in quarters. Put the two halves next to each other, face up, in the microwave.  It’s best to place it slightly off-center, as microwaves have hot-spots and “nodes” and the center is a “node” of radiation.  Press go.  Click here to read the rest….

I’ve been wanting to do a series of posts on Fun Things To Do with a Microwave, and I’m just going to get off my butt and DO it!   For some of these to work well, you need to know where your microwave hot spots are.

What do we mean by hot spots?  Microwaves are just one form of radiation — like x-rays or visible light — of a particular frequency.  The reason they chose microwave frequencies for ovens is that this frequency is more readily absorbed by water.  The microwaves are pretty long (about the size of a grape, as you’ll see in the next post), so you get a regular pattern of peaks and troughs (or hot and cold) as the waves add and subtract  (it’s a checkerboard, like two-slit interference).  You may have noticed that food cooks slower at the center of a microwave and faster at certain other places (that’s why those rotating plates are handy).

Method 1:  THE WATER METHOD  (From RealSimple)

You can find the hottest parts of your microwave by placing custard cups or small bowls filled with water all around the oven. Heat for 1 to 2 minutes, checking every 30 seconds. The ones that boil first are in the hot spots.

Method 2: FAX PAPER gives a more permanent map (from

Take a damp paper towel and place it on top of 5-10 other paper towels in the bottom of your microwave. On top of it, place a sheet of themally sensitive fax paper, the kind that old crappy fax machines use. Credit card recipts also work, but they’d be harder to tile the bottom of your microwave with. The extra towels at the bottom provide some insulation. Turn the microwave on for a while. The first areas on the paper to turn dark are the hot spots.

Method 3: MARSHMALLOWS (or chocolate chips)

Or a tasty way is to place marshmallows all over the bottom of the oven (might want to put a paper towel down first).  Greater pixel resolution with the tiny marshmallows (more Marshmallows Per Inch!)

Here’s a kid-friendly explanation of microwaves (as well as a simulation of the marshmallow method) and a kid-friendly explanation of hot spots.

tt_icon_170In keeping with my previous post on the International Year of Astronomy, this week’s 5-minute  Science Teaching Tips podcast is about our perception and the size of the moon.  What coin would just barely cover the full moon? You may be surprised. TI director (and recovering astrophysicist) Linda Shore explains how our brains distort the actual size of the moon. Listen to the full podcast — When the Moon Hits Your Eye.

Amateur astronomer in Negev desert, Israel

Amateur astronomer in Negev desert, Israel

Happy New Year!  It’s yet another year that’s been designated the International Year of Some Great Big Science Topic (last year was polar year).  This year it’s the International Year of Astronomy, and there are quite a few fun-packed astronomical events for the whole family.  See a whole list of astronomical events for 2009 here.  And here is a nicely formatted document (PDF) with astronomical events (some particular for viewing in the Denver area) for the year.  Note that you can Ask An Astronomer (DU Prof Robert Stencil at rstencel AT du DOT edu) your questions about the sky.  (And don’t forget my friend Tom’s Skyguy video blog of astronomy questions for kids!)

For those of you in the Denver area, note the monthly gatherings at the Historic Chamberlin Observatory near the DU campus for the celebrations of the 400th anniversary of the old 22-foot telescope.  The DU press guy tells me that this would be “a great place for a high school student interested in astronomy to meet up with a professor or two in a casual environment.”

You can see the observatory website with all special events at

I’m starting my own business, doing freelance science education, writing, blogging, podcasting, and anything else that comes my way.  (Got a contact or job for me?  Send it my way at riggmailgeek at yahoo dot com — resume here.  My experience is broad, but in a nutshell I’m well-suited to create innovative education and communication programs about science for the public, or for K-12 teacher professional development, using writing, podcasting, and inquiry-based learning).  So, dear readers, got any clever ideas for a name?  I’m thinking the obvious “sciencegeekgirl incorporated” though I’m not quite sure if the “incorporated” is kosher given that I’ll be an LLC.  Ideas?  Tips on setting up your own freelance biz?  All help and creativity appreciated!radio-geek_sm