Sol Robbins asked me a question as to what material(s) I use for my color planetary observations. This has to be explained in more detail.
I have always found it difficult to accurately render color upon the disk (on an observing form) of a planet, especially a multicolored planet such as Jupiter. What I would consider a "red" color upon the surface of Mars another observer may call "salmon." The question of color upon the surface (or atmosphere) of a planet is therefore a subjective one (unless measured photometrically of course). Several factors affect the visibility of colors upon the surface/atmosphere of a planet.
The eye itself is the primary factor that must first be addressed. Light entering the eye is focused by the lens and an image is formed upon the retina. The retina of the eye is composed of photoreceptors, namely the rods and cones. The cones, involved with color perception, are located primarily in the central zone of the eye, especially over the macula. The rods, involved in the perception of shades, are located towards the periphery of the retina (http://www.tedmontgomery.com/the_eye/index.html). A certain amount of light must strike the cones within the retina of the eye for the perception of color to take place. This depends upon the luminance (or brightness) of the object (candles/meter (squared)) and for our purposes while observing objects with small angular diameters (e.g. planets) this is a function of aperture.
The aperture of an instrument is vital in the detection of color upon the surface/atmosphere of a planet. Apertures smaller than 5 to 6 inches (or ~13-15 cm) will allow color to be visible upon the surface/atmosphere of a planet, but the limited light transmission of the objective (lens or mirror) may not allow subtle (or faint) colors to be perceived by the eye (retina). Some observers may now be saying "I can see many colors over the planets with my fine 4-inch refractor" and while this is true many delicate colors (especially over a planet such as Jupiter) will be missed using a smaller aperture. A good experiment is to place a quality 4-inch refractor (assuming acceptable suppresion of chromatic abberation) next to an 8-inch reflector and point both instruments at a planet (e.g. Jupiter). While the 4-inch refractor will provide a sharp and high contrast image of the planet the larger reflector will show the colors visible much more readily. This is not an attack against smaller apertures but only a scientific fact.
I have always found it difficult to accurately render color upon the disk (on an observing form) of a planet, especially a multicolored planet such as Jupiter. What I would consider a "red" color upon the surface of Mars another observer may call "salmon." The question of color upon the surface (or atmosphere) of a planet is therefore a subjective one (unless measured photometrically of course). Several factors affect the visibility of colors upon the surface/atmosphere of a planet.
The eye itself is the primary factor that must first be addressed. Light entering the eye is focused by the lens and an image is formed upon the retina. The retina of the eye is composed of photoreceptors, namely the rods and cones. The cones, involved with color perception, are located primarily in the central zone of the eye, especially over the macula. The rods, involved in the perception of shades, are located towards the periphery of the retina (http://www.tedmontgomery.com/the_eye/index.html). A certain amount of light must strike the cones within the retina of the eye for the perception of color to take place. This depends upon the luminance (or brightness) of the object (candles/meter (squared)) and for our purposes while observing objects with small angular diameters (e.g. planets) this is a function of aperture.
The aperture of an instrument is vital in the detection of color upon the surface/atmosphere of a planet. Apertures smaller than 5 to 6 inches (or ~13-15 cm) will allow color to be visible upon the surface/atmosphere of a planet, but the limited light transmission of the objective (lens or mirror) may not allow subtle (or faint) colors to be perceived by the eye (retina). Some observers may now be saying "I can see many colors over the planets with my fine 4-inch refractor" and while this is true many delicate colors (especially over a planet such as Jupiter) will be missed using a smaller aperture. A good experiment is to place a quality 4-inch refractor (assuming acceptable suppresion of chromatic abberation) next to an 8-inch reflector and point both instruments at a planet (e.g. Jupiter). While the 4-inch refractor will provide a sharp and high contrast image of the planet the larger reflector will show the colors visible much more readily. This is not an attack against smaller apertures but only a scientific fact.
