PREVIOUSLY, I HAVE DESCRIBED my picks of some of winter's finest open clusters. Now I'd like to share a selection of favourite summer clusters. There are, of course, far too many to choose from, including some of the most famous clusters in the sky. Our tour on these pages will take us to a few of those famous clusters, but many others are overlooked members of this class of deep sky object.
We'll begin with the Pleiades (M45), a star cluster that features prominently in many of the world's diverse cultures. I've always liked the poet Alfred, Lord Tennyson's reference:
Many a night I saw the Pleiads, rising thro’ the mellow shade, Glitter like a swarm of fire-flies tangled in a silver braid.
Last summer, on an evening with excellent transparency, I counted 12 Pleiads with the unaided eye from my backyard. I spotted the brightest seven plus magnitude-5.5 Celaeno, magnitude-5.6 18 Tauri, magnitude-5.8 Asterope (counted as two since Asterope was elongated, even if I couldn't split the pair that are separated by 2.5’), and the magnitude-5.4 star HD 23753 that lies 42’ south-southeast, Irish astronomer Agnes Mary Clerke wrote that Kepler's tutor, Michael Mästlin, “perceived fourteen, and mapped eleven Pleiades previously to the invention of the telescope.”
