Harry observes NGC 2516 and calls it “The Fishers” cluster



NGC 2516 cluster in constellation Carina – “The Fishers” cluster? Sketch and copyright Harry Roberts ©, all rights reserved

Regular correspondent and solar observer Harry Roberts reports on his observations of the star cluster NGC 2516.

NGC2516: Southern “Fishers”?

Far southern skies hold wonderful sights for small ‘scopes. My old soviet 4-inch Mak was not meant for astronomy –but makes a fine ‘scope for comets – and many other things.

In 2012 it was used to sketch NGC2516, the nameless cluster at the ‘foot’ of the ‘False Cross’ in Carina, from an urban balcony. It did a good job: pin-point stars and no false colour. Most southern objects lack common names, so we must talk four digit “NGC-ish”. NGC2516 (says the Web) is called the “Running Man” (same as the one in Orion!) or, the “Sprinter”; I’ve heard neither used. I’m tempted to dub this cluster “The Fishers”, as I’ll later explain.

NGC2516 is a bright, box-shaped, rich cluster of 80 to 100 blue-white stars (Spectral Type B, mags7-9) – sited amid (or behind?) a field of brighter and colourful foreground stars (Mags~6, types K-M?). The ‘whole’ thing is extremely ‘pretty’ in a wide-field ‘scope. In the e.p. sketch (Fig above), the N2516 cluster is in the bottom half, while the foreground stars are mainly in the top half. Can any other cluster beat this one for colour and richness? I’d love to hear suggestions!

The sketched field is quite large: bigger than a square degree, while the dense NGC cluster is 30-arcminutes diameter, a Moon’s width! This means it’s an easy naked-eye object at mag3.8, a great target for bino’s and rich-field ‘scopes, but not big ‘scopes with narrow fields maybe. Lacaille found it in his ½-inch refractor in the mid-1700’s: the ultimate small ‘scope!

Doubles. There are several multiple star groups in this cluster field: a triple is noted on the sketch. There are more to be seen (the sketch is not so detailed) – but photos often hide them in the halo of brighter stars. Search and you will find them.

Nebula?  Reference images of this cluster show some residual nebulosity, it’s common in clusters of type B stars (and in 20% of all clusters). I’ve not seen any here– but big ‘scopes with filters might well detect it. Sky-Cat 2000 does not list any for NGC2516, however.

Naming. To return to this question: there’ve been attempts at common names in recent years – often with very prosaic results. I’d hate to see this wonderful stellar assembly called the ‘handcart’ or suchlike!

The Fishers Cluster? To me it suggests a line of native fishers after dark, some holding firebrands (the red stars), about to net a shoal of silvery fish (NGC2516). The fish dart this way and that to escape. Will they be caught? It’s a timeless scene in Oceania: the fishers at work in the dark. Maybe this name will stick?

Take a closer and more regular look at this showpiece cluster; we can use both wide fields and high powers with great results- and it’s visible for much of the southern year. Clear skies!

Harry Roberts is a Sun and Moon observer, a regular contributor to the Sydney Observatory blog and a member of the Sydney City Skywatchers.

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