is probably red in color. This is a much more objective way to confirm the color of a feature, as opposed to viewing in integrated light since different observers can perceive color differently. For example, if you find it difficult to discern where the preceding and following edges of the GRS are, try using a blue filter.

Red filters, such as Wratten 21 (light orange-red), 23 (light red), or 25 (red) can assist in the identification of blue features such as the projections, festoons, and the bluish-gray features on the southern edge of the North Equatorial Belt. Red filters can also help you see really subtle features, like the south temperate oval BA, especially when a collar of bluish-gray material surrounds the oval.

Blue filters, such as Wratten 82A (light blue), 80A (medium blue), or 38A (blue) can be used to enhance red features, such as the Great Red Spot and the reddish-brown equatorial belts themselves. Since blue filters enhance, or darken, the equatorial belts, they help increase the contrast of bright features imbedded in the belts such as bright ovals and rifts. This is especially helpful when trying to accurately identify and measure the preceding and following ends of a rift or when measuring the length of a large bright oval.

I like to use yellow filters such as Wratten 12 (medium yellow) and 8 (light yellow) to observe the polar regions. Many veils and shadings have been observed in yellow light. South temperate oval BA can often be enhanced using the Wratten 8 filter, to distinguish it against an otherwise grayish background. I especially like the Wratten 8 filter as a general-purpose contrast enhancer. For me, this filter seems to increase overall contrast gently without washing out the more subtle features. I have also used green filters effectively. Wratten 11 (yellow green), 56 (light green), and 58 (green) will also enhance red and brown features.

Filters are usually threaded so they can be screwed into the field end of the eyepiece barrel. As with eyepieces, filters should be of good quality, squarely and securely mounted in their mountings, and optically flat on both surfaces. Filters should be kept clean of lint, dirt, and smudges so as not to obstruct the fine detail you are attempting to observe.

Again, there are varied opinions about filters, and the you should experiment to see which filters work best for you. Depending upon observing conditions, observing without a filter can sometimes prove to be the best choice.

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