Is there Color in Astronomy?

It’s not just astronomy. The question encompasses everything we see.

When I observe Jupiter, I can separate colors in the belts and zones. I see bluish colors, brown-reds, brown yellows. When I look at Mars, I see orange. Saturn is a beautiful creamy yellow, Neptune a startling blue. On a brilliant clear day, the sky is all kinds of blue. Sunsets are a riot of reds, oranges, yellows, blues, and everything between. Then there’s the green flash – just as the Sun gets below the horizon. Ever see that?

Look at the images produced by astrophotography, colors!

Isaac Newton proposed there are no colors in our universe, that what we perceive as color is in our heads. Philosopher David Hume described color not as a quality of objects, but as a perception in the mind. Most physicists subscribe to this concept. Why? How?

It’s the electromagnetic spectrum.

Everything that produces heat also produces electromagnetic waves. The hotter it gets, the shorter the wavelengths get. Also, electromagnetic waves are reflected by objects, and the reflected wave is usually at least a little different, based on the object’s own wavelengths. It’s a big mashup.

The section of electromagnetic spectrum we are concerned about here is the visible spectrum. You might know ROY G BIV (Red, Orange, Yellow, Green, Blue, Indigo, Violet).  Our eyes are sensitive to the visible spectrum, that’s why we call it the visible spectrum and that’s why it has those “colors”. If we could see infrared, or ultraviolet wavelengths they would be considered visible too. Some animals can detect infrared or ultraviolet, but we don’t know how it shows to them. Since we don’t see them, when we make detectors that do see infrared or ultraviolet, we don’t know how to present their images as they would be to us. We just make them white or give them a color artificially.

After millennia of evolution our eyes, however, can finely parse out that section of the electromagnetic spectrum we perceive. The wavelengths get represented as a colorful continuum, with seemingly infinite variations. How many colors can your TV reproduce? Some of the newer screens can show a billion colors! Just think about the challenge of deciding on a color for your living room with that many choices.

So, answering the question I posed in the title: Well, no, and yes. Objects do not have color, but we process their emitted or reflected wavelengths as color. We make film and digital sensors that detect and process those wavelengths as do our brains. Understanding this helps us visualize non-visible wavelengths by assigning those wavelengths a unique color that stands out from the visible wavelengths in an astronomical image.

Color might not be an object’s innate quality, but our perception of color can give it a quality and make us feel it.

What’s in the Sky

June 21; 9:58 am CDT: Summer Solstice

June 21: An hour after sunset; west: A waxing crescent Moon meets up with Venus and Mars. Should be pretty.