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The Caldwell Objects

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Nicolas Louis de Lacaille, however, is credited<br />

with first describing it as a star cluster. It is the<br />

fifth object listed in his 1755 catalog's Class II<br />

(Nebulous Clusters). In his ½-inch 8x telescope<br />

he saw it as a "small star group."<br />

Whenever I take my first naked-eye glance at<br />

this cluster, I immediately see a double star,<br />

oriented northwest-to-southeast, whose components<br />

are separated by about 20'; these "stars"<br />

are Omicron Velorum and what is actually the<br />

combined light of a magnitude-5.5 star<br />

andamagnitude-4.9 star, themselves separated by<br />

less than 2'. With a little more time, a magnitude-<br />

5.5 star pops into view about ½° southsouthwest<br />

of Omicron Velorum. <strong>The</strong>se stars form<br />

a tight naked-eye triangle. Now return to<br />

Omicron Velorum with averted vision. Does it<br />

look fuzzy? It should, because it is the brightest<br />

of three naked-eye stars that form a tiny (10'long)<br />

arc running from northeast to southwest.<br />

Can anyone resolve these stars with the unaided<br />

eye? Try to do so in the twilight.<br />

In 7x35 binoculars the cluster's main body<br />

comprises about a dozen suns. <strong>The</strong>se stars form<br />

an asterism that, to me, looks like the<br />

85<br />

stick figure of a woman extending an arm to the<br />

southeast. In her hand is a pillow (the close pair<br />

of magnitude-5.5 suns and others). And atop that<br />

pillow is a diamond tiara formed by a tight<br />

sprinkling of 8th- to 11th-magnitude suns. It<br />

looks like a tiny cluster-within-a-clus-ter. <strong>The</strong><br />

view is better yet in the Genesis at 23x. <strong>The</strong> star<br />

immediately south of aqua-tinted Omicron<br />

Velorum burns with a lemony hue. Among the<br />

roughly two dozen suns readily visible in the 1°wide<br />

cluster, several pairs can be seen, and many<br />

of these make up the tiara. If we accept the<br />

distance tabulated on page 339, this loose cluster<br />

is spread across 9 light-years of space. <strong>The</strong> stars<br />

are scattered unevenly, and no point forms a<br />

distinct visual center. In fact, Archinal's latest<br />

data shift the cluster's center northward to<br />

Omicron Velorum, creating an even more<br />

disturbingly asymmetric picture. Imagine how<br />

different the view of the night sky would be from<br />

hypothetical planets orbiting various stars in this<br />

lopsided cluster.<br />

Contrary to some reports, IC 2391 does have<br />

appeal under higher magnification. At 72x, for<br />

instance, about a dozen suns burn forth amid a<br />

bright trapezoidal asterism, inside of which lies a<br />

smattering of various scintillating suns. It looks<br />

as if Orion's Trapezium has been magnified 1,000<br />

times over without any loss of image quality.<br />

Omicron Velorum and its two bright<br />

counterparts each sport one companion or more.<br />

<strong>The</strong> pillow-and-tiara region also stands apart,<br />

surrounded by blackness.<br />

Before moving on, hop about 1° due east of<br />

Omicron Velorum to the 12'-wide open cluster<br />

NGC 2669. Also known as Harvard 3 (H3) on<br />

some charts, it's a neat little 6th-mag-nitude<br />

cluster of about a dozen or so suns, with four<br />

prominent pairs forming a mirror-image Greek<br />

letter lambda (λ). Can you see it with the<br />

unaided eye?<br />

<strong>The</strong> <strong>Caldwell</strong> <strong>Objects</strong> 341

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