Observation and Estimates of Color

g g In Chap. 3 we discussed the observation of color in Jupiter's atmosphere and I

encourage the reading of that section again. We discussed how subjective and inaccurate the observation of color can be and how some of our predecessors, pillars of the amateur astronomical community, have dealt with the subject. In spite of the

difficulties, I must admit I consider the study of color in Jupiter's atmosphere to be one of the most pleasurable and intriguing parts of my passion for the planet.

The contrast of colors in Jupiter's atmosphere is very subtle. You may have particular difficulty discerning from among the different shades of gray, brown, alabaster, and ochre; and we have already discussed how the GRS isn't so red after all, at least at the present time! So, if the determination of color is so difficult and subjective, of what use is the endeavor?

I believe that, as with drawing the planet, the study of color trains the eye to see. It improves our skills and makes us a better observer. It will train the careful, honest observer to be all the more mindful of the integrity of his observation. Over time, the observation of color in a consistent manner can provide useful data regarding trends in Jupiter's atmosphere. We have referred to "coloration events" in Jupiter's Equatorial Zone. We have discussed the fadings and "Revivals" of the South Equatorial Belt and the subsequent increase and decrease in intensity of the GRS. Belts fade and are restored. All of these events are impossible to discuss without introducing some discussion of color. The great history of Jupiter is replete with the discussion of color by past observers. It is as though the discussion of color in Jupiter's atmosphere is ingrained in the human spirit and we should not deny it to ourselves.

It is my practice to record the color of Jupiter's belts, zones, and other individual features on the Jupiter observing form. I generally make this determination while I am making intensity estimates. I find that estimates of color, as with intensity estimates, are best performed at lower powers of magnification in integrated light; that is, without the use of color filters. With a Celestron C8 I usually do this at a magnification not exceeding 175x. With a 12-in. instrument I would use a higher power. Excessive magnification causes the image to be dimmer, and the color to be more diffused or diluted. The intensity of the color needs to be strong enough that your eye can make a reasonable estimate of its tint and intensity. I also like to record this information in the descriptive notes of my observing log, a log that I keep for all of my astronomy observations, including the non-planetary ones. As subjective as it is, we never know when our record of color will turn out to be the most important piece of information recorded on a given night.

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