Waves Traveling the Universe

Visible light is arguably the most familiar part of the electromagnetic spectrum. In this part of the lesson, you will reacquaint students to thinking of it in terms of waves. Paraphrase:

Of the vast spread of the electromagnetic spectrum, just a tiny bit is visible. Everything we see is light... or the absence of light.

Visible light includes a nearly infinite number of frequencies, but we think of that part of the spectrum as ROYGBIV (red, orange, yellow, green, blue, indigo, violet).

When we see an object that is red—for example a bright red apple—the apple’s skin is absorbing all the colors of the visible light spectrum, except red. The red frequency is not absorbed by the apple’s skin, so it reflects off the surface of the apple and back to our eyes!

Ask:

Look at what you and your classmates wore to school today. What color is reflected in each piece of clothing? What colors are absorbed?

Students may ask about the difference between light and pigments. They may also ask about why we see light blue, or pink, or even fuchsia, or teal, colors that are not part of the electromagnetic spectrum that we often teach as "ROYGBIV."

You may want to address the different ways colors combine in light (known as "additive color" because combined colors add up to white). Consider paints, crayons, inks, and all the ways students may be used to thinking about color in, for example, art (known as "subtractive color" because colors combine to become darker). This difference is shown in the optional slide.

Note: if your school uses uniforms or you don't want to encourage the students to be looking at one another's attire, you can ask the students to look at objects around your room instead, or use the photo provided, and ask:

Look at this classroom. The students are wearing different colors. What color is reflected in each piece of clothing? What colors are absorbed?

Students consider how what humans see compares to what butterflies and snakes see.

Paraphrase:

What is visible to humans is often not visible to other animals, and vice-versa. Some animals' eyes see a greater range of frequency than humans can.

For example, some animals see ultraviolet (UV) light, a slightly higher frequency than the violet end of the spectrum visible to humans. Butterflies, bees, some birds, reindeer, sockeye salmon, and scorpions all see some of the UV part of the spectrum. They don't have much in common with one another.

Ask:

Why might these animals be able to see ultraviolets that we cannot?

Possible answer:

They have evolved to be able to see in the world what is important to their survival. Insects can see patterns on flowers that help them find the nectar. (More on this topic in the rest of the lesson.)

Another fun fact to paraphrase:

On the other end, some animals see in the infrared range: snakes like pit vipers and boa constrictors, piranhas and other species of fish (even goldfish), and mosquitoes.

Ask:

Why might these animals be able to see infrareds that we cannot?

Possible answer:

They have evolved to be able to see in the world what is important to their survival. Snakes are looking for movement of prey, so having a heat map allows them to pinpoint it in their environment. (More on this topic in the rest of the lesson.)

Explore how insects use a different part of the spectrum to see three flowers.

Ask:

What does A B C? (a bee see?)

Show: Slide with photographs of flowers (buttercup, forget-me-not, pansy) taken with ultraviolet light, visible light, and infrared light. Some flowers have hidden UV markings, known as nectar guides. Bees and other insects can see ultraviolet light, and may find these markings attractive.

Ask:

This slide shows three flowers as if seen by eyes sensitive to three different parts of the electromagnetic spectrum. Which of these images do you think shows what is seen within the visible light part of the spectrum? infrared? ultraviolet?

Answers: top row is UV, middle visible, and bottom is IR.

Paraphrase:

In the buttercup on the left, in visible light (the middle image) the flower has bright yellow petals with bright yellow stamens surrounding a slightly darker yellow-green cluster of carpels at the center. The stem and leaves are green in color and much darker than the flower.

In ultraviolet (the top image), veining is seen much more clearly on the petals. The base of each petal has a very dark marking (a nectar guide). The carpels and stamens both appear dark as well. The stem and leaves are also dark.

In infrared (the bottom image) the carpels appear with the same brightness as the stamens and petals. The stem and leaves also appear much brighter than they do in visible light.

The same higher-contrast nectar paths are seen in forget-me-nots (the center column). The old flowers appear much brighter than new flowers in ultraviolet. In the pansy (right column), however, there do not appear to be any UV-visible nectar guides, but damage to the flower's petals is more obvious in UV. The markings around the center of the flower are most prominent in visible light.

Note: Flower images and explanations by David Kennard, licensed CC-BY-SA 4.0.

Have students open the slide with the visible / ultraviolet sliders. Allow them a few minutes to explore the pattern differences in the flowers.

Paraphrase:

Insects and snakes see the world differently than we do. That's because their visual systems respond to a different part of the electromagnetic system than human eyes do.

Imagine traveling to another planet where animals can access different parts of the electromagnetic spectrum. What would they “see” when they look at you? What if an alien animal could see microwaves, or even X-rays? Would they see your spaceship? What about you?

Give students adequate time to think about the writing prompt and write a few paragraphs about their ideas.

For your creatively challenged students having a hard time getting started, generate some sentence starters, such as:

When we landed on Planet X, we noticed the creatures swarming our spaceship, but they took no notice of us. Were we invisible to them? Dr. Candace, a biologist by training, made some observations...

Possible focus for students who want an extra writing challenge:

Re-imagine a science fiction story you like—it could be a short story, comic book, novel, show, or movie. How might an "alien" from another planet see the action of the movie differently than the human characters and audience saw it?

Not a science fiction fan? Choose an earthly animal of another species whose visual systems work differently than our own, and imagine a scene as viewed from that animal's perspective.

Extension and ELA connection: Add a reading from Madeline L'Engle's A Wrinkle in Time. You may use an excerpt either as a follow-up or as a context-setter. In Chapter 11, "Aunt Beast" tells Meg, "We do not know what things look like, as you say.... We know what things are like." Both Meg and Aunt Beast spend quite a while trying to understand how their new friend perceives the world around them.

Beings seeing

Imagine traveling to another planet where animals see different parts of the electromagnetic spectrum. What would they see when they look at you? Could you see them? What if an alien animal could see microwaves, or even X-rays? Would they see your spaceship? What about you?

In your writing, you may want to use some of the words you've
encountered while learning about waves, such as:

electromagnetic • spectrum • visible • radiation
ultraviolet • infrared • radio • microwave • transmission
medium • wavelength • frequency •  analog • digital