Astro demos

A friend asked me to come to her daughter’s 3rd grade class to talk about astronomy and my research in exoplanets. So I teamed up with two other women in my department who are finishing up their PhDs, to bring a range of perspectives to the kids. For this kind of class we wanted to do a few simple but engaging demos related to the kinds of things astronomers measure. Between the three of us we had 2 observers, a theorist, and some instrumentation experience.

For my part I picked up one of my favorite teaching tools, a package of pocket diffraction gratings made by These are pretty cheap so you can give them away to a full class of kids. Along with this, I wanted to bring a non-white light source, but I didn’t have access to any sort of gas tube lamps and for some reason had trouble finding LED flashlights that were true “single color” LEDs (as opposed to a white light with a colorful cap. It is however easy to purchase a large number of individual diodes of different colors, resistors, and a small breadboard for less than $15.

So as long as you remember how a breadboard works (give me a break, it’s been almost a decade since I used one), this is a pretty simple and cheap solution.


Above are red and blue LEDs with the appropriate resistors and 9V battery sources. Please don’t mind the shoddy wiring to the batteries (yes that is scotch tape), like I said, it’s been a while, and I don’t have all the nice tools.

With the diffraction gratings, this was a pretty easy way to show 3rd and 4th graders two main ideas:

  1. Different light sources produce different parts of the “rainbow” seen from the white lights in the room.
  2. Even a seemingly “blue” or “red” LED contains other colors in the spectrum. We can use this tool to study what wavelengths (or colors) of light are present.

My best try taking a picture through the grating of my LED setup.


For the second half of the time, we showed a demonstration on gravity and how the movement of objects is affected by massive bodies. This was done with a lycra sheet wrapped around a hula hoop, with balls and marbles of different sizes and masses. Using this demo we were able to talk about how we can detect and characterize very massive objects like supermassive black holes. These two demonstrations were a great way to start the conversation of how and what astronomers measure.

I still have about 200 LEDs of different colors so I’m definitely using them again!

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