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Referring to my observing notes, one of the best views of M22 occurred on the evening of 25 July 1990 with a 20cm f6.7 dobsonian reflector from the light polluted sky of Mt Eden. Employing an eyepiece of low power (48x), M22 appeared as a large and very bright irregular cluster with chains of bright stars radiating outwards to the southwest. A step up in power to 90x magnification showed “fingers” of bright stars overlaid upon a milky-white background of fainter unresolved stars, giving this cluster an obvious 3-D effect. Further observations over the years have not dimmed my enthusiasm for this cluster, truly one of the best of its type available to telescopes.
NGC 6642 is another globular cluster lying around 1° to the northwest of M22. Discovered by William Herschel on August 7, 1784; “globular, pB, R, gpmbM, 2', resolved into visible but vS stars 15..16m”, NGC 6642 appears as a small and faint irregularly round glow, unimpressive to the eye. Large apertures will show brightening toward the central region and a prominent stellar nucleus.
Rich
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