National Aeronautics and Space Administration

Electromagnetic Spectrum Activity

By Maggie Masetti and J. Allie Hajian

Pretend you are from an alien civilization that can only detect the color green. You have just landed on Earth. What would things outside look like? For example, to the left is what a tree would look like if you could only see green and to the right is how it would look to a human.

If you could only see the tree as it appears on the left, what information about trees would you be missing? Think about it as you try this next example.

Suppose you were a biologist studying and trying to understand a flower - possibly tulips. And suppose also that you could ONLY detect things that were green. What parts of the tulip would you know about if you could only detect things that are green?

• What parts of the tulip would you not be aware of?
• Would tulips look the same or different in the summer as they do in winter?
• How would you hypothesize your tulips get nutrients? Reproduce? Grow? How would you figure this out if you could only detect green?

Look at the below image of lilypads. This is what it would resemble if you could only see green. Try running your mouse over the image.

You miss a lot when you have an incomplete picture.

Plant biology would be so different if we could only detect things that are green! Do you think that we would understand as much as we do about plants? Flowers are an important part of a plant and are in fact one way they reproduce themselves. If we could not detect flowers it would be difficult to know how plants reproduced! We could probably not see plant roots either, which would hinder us from learning how plants get nutrition. We couldn't even see soil, so we wouldn't know what the plants were getting their nutrition from!

There would be large gaps in our knowledge of plants and how they work. A similar situation exists in astronomy.

For instance, because of X-ray telescopes, we know that most of the mass of a cluster of galaxies consists of hot gases that emit X-rays but are invisible at optical wavelengths. Because we can't see X-rays, we had no way of knowing this until we thought to look at the skies with electronic eyes. If we hadn't learned about these hot clouds of X-ray emitting gas, we wouldn't know how galaxies form and evolve!

Seeing only green gives us a very incomplete, and even incorrect, picture of things around us. This is analogous to humans only being able to see the Universe in optical light.