Sand and Stars

Carina’s Open Clusters

A cluster of pebbles found in the vastly dry Molopo riverbed

2 Dec 2016

As a keen rockhound, I like to forage along the dry riverbed of the Molopo River with my dog Waldo. The Molopo River is a fossil river – it last flowed perennially over 16,000 years ago (right around the time the light left 47 Tuc). Now it is simply a wide and shallow riverbed, dry, sandy and heavily grassed over in patches.

Here and there ancient pebbles and cobbles are exposed in the cream-coloured sand of the riverbed. The other morning, while I was filling my little sack up with beautiful specimens, I thought how similar finding and examining these clusters of pebbles is to observing open star clusters. And like open clusters, a good look reveals a lot more than just a pretty grouping of little rocks. They come in an array of colours, and some are pearly, some glassy, some earthy, some dull, some translucent, most opaque. Some are fine-grained and delicate, while others are coarse-grained and rough. And they take high magnification well! My loupe reveals incredible intricacies and minutiae.

When it comes to open clusters, I think they are the most beautiful objects in the night sky. I can happily spend an entire night observing them.

Last night little woolly clouds meandered around the sky like a bunch of sheep, but around midnight they melted away, so I spent until dawn in Carina, as this opulent region of the Milky Way offers a treasure trove of open clusters.


10 f/5 Dobs; magnifications of 90x, 144x and 208x 

I turned the telescope first to the open clusters in the Eta Carinae Nebula.


Image credit
Image credit Hubble/ESO

This gorgeous photo shows the northern portion of the nebula. The bright star at the lower centre is η Carinae in the open cluster Trumpler 16, and the irregularly shaped dark region to its right is the Keyhole Nebula. The compact grouping of stars near the pillars and clouds of dust up and to the right is open cluster Trumpler 14. Open cluster Cr 232 is to its left, and Trumpler 15 is at the top centre.

Trumpler 16 

RA 10 45 10.0   Dec -59 43 00   Mag 5.0   Size 10′

Trumpler 16. Image credit Hubble/ESO

This is surely one of the most breathtakingly beautiful open clusters owing to its superstar member that steals the show – the brilliant Eta Carinae, surrounded by its intensely orange Homunculus Nebula. The young cluster contains over 560 stars, including a significant population of very young stars, and three of the biggest and most impressive stars from our galaxy: the aforementioned eta Carinae,  Wolf-Rayet HD 93162, and Tr16-244. After dragging one’s attention away from the Homunculus (another night, another blog), one realises how beautiful the rest of the cluster’s stars are. The  cluster’s brighter stars lie to the SE of Eta Carinae. A pair of lovely short star chains run south and south southeast of Eta, with the other stars scattered around in a random fashion.  

Trumpler 14

RA 10 43 56.6   Dec -59  33 11   Mag 5.5   Size 5.3′

Trumpler 14
Trumpler 14. Image credit Hubble/ESO

This is an absolutely gorgeous little cluster; its sizzling little stars embedded in the magnificent nebulous silky-grey background. There are some beautiful little stars entwined in curving star chains, and to the north there is a charming little knot of about 10 stars. There is a dainty double star towards the eastern side of the cluster.

Trumpler 15 

RA 10 44 44.0   Dec -59 21 00   Mag 7.0   Size 15

Trumpler 15. Image credit Hubble/ESO

This is a beautiful little cluster – small, dainty and striking. There are four short, delicate little star chains that radiate in a tight little formation from a pair of roughly 6 mag stars. The background is a lovely palest silver-grey patina of nebulosity and the cluster stands out beautifully against it.

Collinder 232 

RA 10 44 39.0   Dec -59 33 36   Mag 6.8   Size 4

Collinder 232. Image credit Hubble/ESO

Lying just east of Trumpler 14, this tiny little cluster lies in a richly nebulous region. Five little stars make a wide and flattened “V” shape, with the bottom of the “V” pointing southwards. A few faint little stars lie sprinkled around the V.

After the four clusters in this gorgeous and rich region I went further afield in the Carina Nebula…

Bochum 10 

RA 10 2 08.0   Dec – 59 09 00   Mag 6.2   Size 20

DSS image
Bochum 10. DSS image

This little cluster’s beautiful small stars – with a pretty little loop of faint stars near the centre – stand out well against a really lovely field of nebulosity with dark dusty streaks mixed in – it looks like barely stirred cream in a cup of coffee.


Collinder 228 

RA 10 44 00.0  Dec -60 05 00  Mag 4.4  Size 14

Collinder 228. Image credit NOIRLab/NSF/AURA

This lovely cluster shows a large, scattered gathering of stars that appear as if they are milling somewhat aimlessly around the lucida, a roughly 6 mag star right at the centre of the cluster. A beautiful chain of about 10 stars arcs in a concave fashion along tthe north eastern edge of the cluster. The cluster is surrounded by dramatic bright nebulous patches and inky-dark dust lanes.

Bochum 11 

RA 10 47 12.0   Dec -60 06 00   Mag 7.9   Size 22″

DSS image
Bochum 11. DSS image

A small but relatively bright little cluster, the brightest star in the cluster is a beautiful creamy-yellow star. A pretty pair of star chains define the cluster’s western periphery.

 vdB-Ha 99 

RA 10 38 24.0   Dec -59 11 00.0   Mag –   Size 20

DSS image
 vdB-Ha 99. DSS image

This is a beautiful cluster because its centre is dominated by the gorgeous double star, Dunlop 94 – a bright orange primary with an obvious and fairly bright white companion – lying in a lovely field, some of which is the rest of the cluster scattered around, with a nice little knot of stars to the north of the lovely orange double. 

And then, leaving the Eta Carinae Nebula, I headed over to a burst of stellar splendour…

NGC 3532 

RA 11 530   Dec -58 44 00   Mag 3.0   Size 50′

Image credit ESO
NGC 3532. Image credit Hubble/ESO

This really is a spectacular open cluster. It appears as a large misty pool of starlight to the naked eye. In the 10 x 50 binoculars dozens of stars sparkle against a dazzling fog of starlight. At low power, this open cluster is a breath-taker… a vast throng of stars packed together and criss-crossed by thick lanes of dark dust. Beautiful arms of star chains radiate out in every direction, some of them beautiful spirals of glittering stars. Just as stars colours are best seen with a contrasting companion, so the astonishingly beautiful stars of this cluster are best seen because of the contrasting ink-black rivers of dark dust that flow between them. You can spend an eon in this cluster, its rich and riotous patterns of brilliant starlight and dark dust lanes take the eye on a blazingly beautiful journey.

And then of course, this cluster is famous for Hubble Space Telescope’s slightly blurry First Light Image on May 20, 1990. It centered on the 8.2-magnitude star HD96755 in the open cluster and it wasn’t until December 1993 that the space shuttle Columbia rode to the rescue, bringing Hubble a set of corrective optics that would restore its vision to what it was supposed to be.

But hey, first light is first light! And as Dave Leckrone, who was a Hubble deputy project scientist at the time said: “First light implies that the light goes all the way through the optics and makes its way to the detectors. It’s only when that happens that you can say first light has been achieved.”

NGC 3293 

RA 10 35 49.0   Dec -58 13 30   Mag 4.7   Size 5′

Image credit ESO
NGC 3293. Image credit Hubble/ESO

After the extravagance of NGC 3532, this cluster – also known as the “Other Jewel Box” and the “Gem Cluster” – is a visual treat of another sort. It is an utterly gorgeous little cluster, a dazzling assortment of about 40 or so stars, many of them beautifully coloured, all sizzling against a background of glittering unresolved starlight. Like its larger and more famous namesake, it has a gorgeous trio of coloured stars, a bluish star, a yellowish-white star and the southernmost star, an exquisite golden star. The stars of NGC 3293 are a worthy rival of the Jewel Box.

A long, dark nebula runs to the west of the open cluster, and a tiny one lies immediately to the east. Without a filter there was only a hint of the diffuse emission nebulosity – Gum 30. But the UHC filter showed the cluster is entangled in nebulosity, and the long dark lane and the small dark patch became more obvious.

Trumpler 17 

RA 10 56 24.0   Dec -59 12 18   Mag 8.4   Size 5

DSS image
Trumpler 17. DSS image

This is an exquisite little cluster, lying in a rich star field. It stands out well against the background as a little patch of tiny stars that appear to loop out to the east from a brighter pair of stars. It looks like a tiny little nugget of diamond chips in a field scattered with more diamond chips.

NGC 3114 

 RA 10 02 42.0   Dec -60 06 00   Mag 4.2   Size 35

DSS image
NGC 3114. DSS image

This cluster is large, rich and bright. Its stars, displaying a range of magnitudes, are scattered around in a casual way, but with two beautiful star strings that form a rough sort of “V” that opens to the southeast. The stars exhibit a lovely mix of cool bluish-white stars and warm yellowy-white stars, with one prominent and gorgeous rich yellow star.

Alas, I ran out of night to explore more of Carina’s gorgeous throng of open clusters, so after putting the telescope away, I made a thermos of tea and my dog Waldo and I climbed one of the sand dunes and watched the sun rise.

Copyright © Susan Young 2016