28 The Electromagnetic Spectrum

The Electromagnetic Spectrum , or EMS , is the range of frequencies of electromagnetic radiation. Electromagnetic Radiation is a fundamental phenomenon of electromagnetism, acting as waves and as particles – photons, which move through space carrying radiant energy.

Image of the electromagnetic spectrum. The entire range of energies of light, including both light we can see and light we cannot see, is called the electromagnetic spectrum. It includes, from highest energy to lowest: gamma-rays, X-rays, ultraviolet, optical, infrared, microwaves, and radio waves. Because we can only see visible light, we are put at a disadvantage when we study the Universe because, because it is actively emitting light at all these different energies.
Public Domain | Image courtesy of NASA.

We see the Visible light portion of the EMS, wavelengths of 400 nm to 700 nm. The wavelengths longer than visible light include Radio, Microwave, and Infrared (IR) waves. Visible Light ; sometimes called ROYGBIV , includes Red, Orange, Yellow, Green, Blue, Indigo, and Violet. Visible light is a very small part of the EMS. Shorter Wavelengths than visible light include Ultraviolet (UV), X-rays, and Gamma Rays. Only radio, some IR, and visible light gets through Earth’s atmosphere.

A mnemonic to remember the EMS in correct order from the longer to shorter wavelengths is R eal M en I n V irginia U se X tra G lue.

Image of Andromeda Galaxy in Visible Light. The wisps of blue making up the galaxy's spiral arms are neighborhoods that harbor hot, young, massive stars. Meanwhile, the central orange-white ball reveals a congregation of cooler, old stars that formed long ago.
Andromeda Galaxy in Visible LightPublic Domain | Image courtesy of NASA / Hubble Space Telescope.

Infrared image from NASA's Spitzer Space Telescope shows the Andromeda galaxy, a neighbor to our Milky Way galaxy.
Andromeda Galaxy in IRPublic Domain | Image courtesy of NASA / Spitzer Space Telescope.

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