I remember my mother telling me that objects don’t really have color. The blue I see on a street sign is really just light bouncing off the sign and entering my eyes. My brain interprets those particular rays as blue because of the way they bounce. The blue is in my eyes not on the street sign. I remember thinking she was crazy. Of course she wasn’t crazy, and of course, it is true that everything that we see comes from light rays bouncing off objects and being absorbed by our retinas and passed along the nerve cells to our brains.

When the original Cassini mission to Saturn from thirty years ago was sent out, the planners put together a teaching curriculum that could be used while Cassini laboriously made its way from Earth to Jupiter, and then to Saturn. The curriculum was called Ways of Seeing. I can’t find it on the Cassini website but in essence, it said that all the equipment on the satellite could be considered new ways of seeing what was around in the world.

I rejected this idea for a long time, not understanding at all why my eyes were like an instrument that could determine the composition of the rings around Saturn. Or an instrument that could determine temperature. Things that determine temperature are thermometers and my eyes are not a thermometer. Anyway, a thermometer is a glass tube with a substance in it that expands or contracts as it gets hot or cold. My eyes are not a glass tube! … Of course there are other ways of determining temperature. I’m not a metal stick with a dial on top that can determine the temperature of something cooking in the oven either. …

I came to understand, eventually, that my eyes ARE an instrument that registers certain kinds of waves. In fact human eyes register waves with a certain resonance but, for example, some birds can see waves beyond the edges of human sight. There are flowers that have different patterns in ultraviolet light, and birds that can see those patterns. This recognition really helped me to understand the instruments that we have been sending out to see the solar system. “Seeing” is the process of examining whatever kind of radiation can be read by a certain instrument. I thought of seeing as what appears in the visible spectrum of radiation to the human eye. The instruments on a spacecraft try to pick up different portions of the whole spectrum of radiation, and derive different properties from the different spectra.

On earth we have perfected the art of determining what something is made of by deliberately bouncing rays off the substance in question. Now we put that understanding into space. By the same token, we can measure temperature by measuring infrared radiation. We can determine texture by measuring rays that bounce, instead of touching an object. And we can call this “seeing”.

Crucial to all the different instruments is the brain that interprets the different kinds of measurements. First, the “brain” in the satellite that collects measurements and changes them into a statement of temperature, and then the much more important brain in the human that studies what the satellite transmits.