A number of hurdles present themselves when attempting to observe the color of a celestial object from Earth. The type of telescope and optics is very important, and a reflector used in combination with high quality eyepieces is usually the better choice since it will minimize the effect of chromatic aberration.

Earth's atmosphere, or more specifically atmospheric dispersion, is a major source of trouble. Earth's atmosphere introduces chromatic effects that at low altitude are considerable and are particularly apt to vitiate color estimates in the case of a belted planet like Jupiter. The greater density of the air near the ground, compared with that at higher altitudes, not only brings about the well known effects of refraction but also causes the image of a point source, like a star, to appear as a short vertical spectrum with the violet at its upper and the red at its lower end. Under telescopic magnification this is especially noticeable, and in the case of a planet whose upper limb (lower in the telescopic image) may be seen edged in blue, while the lower limb has a reddish border. For a belted planet like Jupiter with bright zones, blue and red light will spill over from the edges of the bright zones and color the edges of the adjacent darker belts [86].

The use of color filters of known wavelength transmission can eliminate the subjectivity in determination of color. It can be noted that when observing Jupiter with a blue filter, the GRS appears darker, as the red light is not transmitted. Likewise, the GRS will appear bright when observed with a red filter. Filters can be used visually, or with photography and CCD and webcam imaging. Filters of known transmission are very useful scientifically and more will be discussed about their use later.

When describing color on Jupiter, it is probably wise to avoid thinking in absolute terms. The GRS is not red but reddish or reddish-brown, or salmon-orange, or pinkish. The belts are not brown or gray, but instead reddish-brown or grayish. There are shades of gray, shades of browns or ochre, colors tending toward something; however, there are no absolutes.

One of the most intriguing methods for removing subjectivity from the observation of color is put forth by Dr. Julius Benton. Benton is the Coordinator of the Saturn Section of the Association of Lunar and Planetary Observers. Visually made absolute color estimates should be carried out by comparing 'the planet' with a satisfactory color standard, according to Benton. Estimates of absolute color have to be made with instruments in integrated light (no filter). The A.L.P.O. Saturn Section has carefully investigated a suitable color standard, and it employs some 500 colored paper wedges for comparative use. One should have normal color vision for this type of work, and the color standard should (ideally) be illuminated by a tungsten lamp filtered with a Wratten 78 (W78) color filter [87].

In spite of the difficulties in determination of color, it continues to be important for observers of Jupiter to study and characterize color, including the patterns of change in coloration and intensity.

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