The Secret Message (in Ultraviolet Light)

Have a bottle with tonic water ready.  In a moment, I am going to turn on some special lights that contain blue, violet and ultraviolet light. We will see the blue-violet but we cannot see ultraviolet; we may detect the ultraviolet by looking at certain objects in this room. Besides hydrogen, there are many other […]

Invisible Colors

When we were looking at the spectrum of white light (the rainbow) we noticed that we cannot see any colors beyond violet or red, but there are actually colors there. Special instruments and special photographic film can detect them. Besides ultraviolet and infrared there are many, many other colors of light. Maybe you have heard […]

What Stars Are Made Of

Astronomers use diffraction gratings to discover what stars and other glowing objects are made of. They do it by analyzing (or breaking apart) the light that comes from a star. Some stars give off light like this.  Put the hydrogen tube on its power supply, turn it on and turn off the white light. Make […]

Diffraction Gratings

Using filters is one way of separating light into its individual colors. Another way of separating light into its component colors is using a “diffraction grating.” Window D in your color analyzer is not just a clear window, it is a piece of plastic with thousands of parallel grooves called a diffraction grating. When light […]


We just looked at light reflected from objects like cloth. We will now look at how light goes through certain kinds of windows. I am handing out some devices that we call “color analyzers.” When you get yours, look for four windows—each of them labelled with the letters A, B, C, and D. VISUAL (alternative movie): Filters If your presentation is not using […]

The Magic Cloth

Now, let’s go back to a red star and examine a piece of cloth (or color pattern on paper).Space travelers call it “the mystery cloth” because they have a hard time agreeing on the colors they see on it. Make sure only the red light is on. While you talk, start unrolling the multicolored cloth […]

What Color Are Your Blue Jeans?

Visit to a planet orbiting a red star DIGITAL EFFECT: Red LightFill the dome with red light to flood the planetarium, all other lights out.Alternatively, if your dome has its own red-green-blue lighting system (e.g., cove lighting), you may use that instead of the red light effect.[We are taking a liberty here: a real red […]

Colors and Temperatures of Stars

Now, let’s find some stars that have a different color than usual. Can you find any stars that have some unusual color, different from white, yellow, silver? If you would like to point it out to the rest of us, raise your hand so that I can give you a light pointer. Demonstrate pointer. Have […]