The power of unseen light

Megan Watzke thinks about light a lot. Watzke is press officer for the Chandra X-ray Observatory, and she’s the co-author of three books: Light: The Visible Spectrum and Beyond (Black Dog & Leventhal, 2015); Your Ticket to the Universe: A Guide to Exploring the Cosmos (Smithsonian Books, 2013); and Coloring the Universe: An Insider’s Look at Making Spectacular Images of Space (University of Alaska Press, 2015). Watzke gave a talk about Light at Town Hall Seattle last week.

Watzke pointed out that there are seven different categories of light, and we’re all familiar with them all, and yet sometimes we forget that it’s all just light.

“Light in its various forms is not different,” she said. “It’s the same phenomenon, it’s just different wavelengths.”

“We use these different types of light every single day,” Watzke added, “or we’re affected by them every single day.”

Watzke said the seven categories are a bit arbitrary and move around a bit depending on the science being done. But they all share similar characteristics. They travel at the same speed, and can bounce and bend or be absorbed or blocked. It’s at different wavelengths that it does different things, and the wavelengths can vary from miles to less than the width of an atom.

Seven categories of light

Radio waves. The longest wavelength, Watzke pointed out that we don’t actually hear radio waves, but that electronics translate the changes in compressed air created by sound. But our mobile phones, GPS devices, bluetooth headsets, MRI tests, and garage door openers all use radio waves.

Microwaves. We use them to cook things, and satellite TV trucks use them to beam video around the world.

Infrared light. Infrared light has many uses. Your TV remote control employs infrared, which can also be used to create warmth. Astronomers can see celestial objects in the infrared when visible light is blocked by interstellar dust.

Visible light. A tiny part of the spectrum. Watzke said that if all of light was a piano keyboard, what we can see would be a few keys around middle-C. But it’s important, as it is why we can see things, is a source of sustainable, non-fossil-fuel energy, and is a key to photosynthesis.

Ultraviolet. UV light can cause sunburn, but can also be useful to destroy microbes, and is used for security on currency or credit cards. Ultraviolet also includes black light, which Watzke joked is an “important part of raves and Halloween parties.”

X-rays. We all know about the medical uses of X-rays, which can cause cancer or be used to combat it. In astronomy objects emit X-rays if they’re extremely hot or energetic, like material falling into a black hole.

Gamma Rays. Watzke called gamma rays the “most energetic thing we know about.” They can be harmful, but like ultraviolet can kill microbes and also has uses such as the sterilization of food.

False color

Author Megan Watzke explained the powers
of the different wavelengths of light during
her talk Dec. 8, 2015 at Town Hall Seattle.
Photo: Greg Scheiderer.

Watzke took some time to talk about the term “false color,” which she finds to be a misnomer. She said false color is not fake color. When scientists create images in false color they are simply trying to represent light that we cannot actually see.

“What is done with scientific images that involve invisible wavelengths is that color is applied to wavelengths and then stacked together, frequently, so you have multiple layers that look like a multiple-color image,” Watzke said. “These are real data, but a layer of color is applied.”

“It’s translating the data that is invisible into something that you can actually see,” she added, comparing the process to the way one would use color to represent different temperatures on a weather map.

She would prefer the term representative color; perhaps it will catch on!

Watzke will talk more about the creation of astronomical images when she discusses Coloring the Universe along with co-author Travis Rector at Wednesday’s meeting of the Seattle Astronomical Society.

Watzke said that she wrote Light to make the topic a little more accessible.

“I want people to understand that light is all around us and that science is all around us,” she said. “Science isn’t something to be scared of or be intimidated by. It’s something that we all should be able to enjoy and pursue.”

More information:

• Recording of Watzke’s talk from Town Hall Seattle
• The trailer for Light, below