When we think about light, we think about what can be seen. If you’ve ever looked through a prism, you understand that white light is actually a collection of all the colors of the rainbow. The visible spectrum consists of all of the light that we can see with our eyes. Let’s go back to the rainbow. The acronym ROYGBIV is a helpful way of remember the colors of the rainbow in “order” where R=red, followed by Orange, Yellow, Green, Blue, Indigo, and Violet. It turns out that red light has a wavelength range of 620-750 nanometers (nm), while violet light has a wavelength range of 380-450 nm. Remember, the shorter the wavelength, the greater the energy. Therefore, because violet light has a shorter wavelength than red light, violet light is higher energy than red light. We have specialized photoreceptor cells in our eyes that are excited by specific wavelengths of light. When white light strikes an object, some wavelengths of light are absorbed by the object while other wavelengths are reflected. The color of an object is actually the wavelength of light that object does not absorb! When reflected light is detected by our eyes, we see color.
Now for the really interesting part: visible light only comprises a small part of the larger electromagnetic spectrum. The shortest wavelength of electromagnetic radiation is on the scale of 10-12 cm (smaller than the diameter of an atom). Remember, the shorter the wavelength, the greater the energy. Photons with the shortest wavelength are called gamma rays and they are powerful enough to shred DNA. We learned about gamma (γ) rays earlier in the school year during our study of nuclear decay (Lesson 15). Viewing the night sky with gamma ray detectors gives us a very different perspective about the structure of space compared to looking with our eyes.
At the other end of the electromagnetic spectrum are the radio waves, with wavelengths on the scale of 104 cm (the height of the Statue of Liberty). Radio waves are emitted by stars and planets and can be detected with radio telescopes. When the night sky is scanned using a radio telescope, we once again see structures in space that are invisible to our eyes.
To learn more about the visible spectrum, gamma rays, radio waves, and all the rest of the electromagnetic spectrum, visit NASA’s Tour of the Electromagnetic Spectrum and prepare to be amazed with the richness of the Universe!
Return to Week 38 – Light and Color and continue working.