Globular Cluster Photo Series (Part 23): NGC 6356

Well. This is a first. Today's globular cluster is the first one I've showcased here on my blog that doesn't have an article about it on Wikipedia. I don't use Wikipedia for all my information but it does make a nice central repository of info, so I had to do a little more digging around tonight. This sort of thing will probably start happening more and more as I exhaust the Messier objects and the brighter or more famous NGC ones. (I already talked a bit about the New General Catalogue in my post about NGC 3201, the first NGC globular cluster I showcased back in March.)

Anyway, NGC 6356. It's located in the constellation Ophiucus at the rather large distance of 49,200 light-years from us. At this distance, I calculate its diameter to be about 115 light-years (since I couldn't find a number anywhere) given its size of about 8.0 arc-minutes on the sky (full Moon is about 30). This would actually make it among the larger clusters of the Milky Way, but its great distance makes it appear small (though it's still among the top 50% of clusters by area on the sky).

NGC 6356 in Ophiucus.

NGC 6356 is also located pretty far from the galactic core outside the galactic plane, at about 24,400 light-years (that's about a quarter of the way across the entire Milky Way galaxy). Most globular clusters are closer to the core (and disk) of the galaxy.

Another interesting thing about NGC 6356 is that it is located about 80 arc-minutes from another globular cluster, Messier 9 (which I wrote about on August 5th). That distance is small enough that I could actually catch both clusters in one picture with a well-placed shot, though I didn't know about it until tonight. Once I found out, however, I was able to match up star patterns seen in both pictures and put them together to make the picture below. Messier 9 is the cluster on the left, while NGC 6356 is the one on the right.

Messier 9 (left) and NGC 6356 (right) in Ophiucus.

While looking at this picture, keep in mind that M9 is about 90 light-years across while NGC 6356 is about 115; it's only NGC 6356's greater distance that makes it look about the same size. Also, since this is two pictures reduced and composited separately, the brightness scale between them is not uniform.

So, all in all NGC 6356 turns out to be a rather interesting cluster for an object not interesting enough to have a Wikipedia page. A hui hou!

Thor's Helmet

Continuing my chain of astronomical images, tonight I have an image of a beautiful nebula, NGC 2359, popularly known as Thor's Helmet after its shape.

NGC 2359, "Thor's Helmet", in Canis Major. North is to the left in this image.

NGC 2359 is about 15,000 light-years away, and around 30 light-years in size. It's a rather unusual kind of planetary nebula. Most planetary nebulae (as discussed before) come about from stars roughly the size of the Sun, gently wafting out the outer layers of their atmospheres as they reach the end of their lives. NGC 2359, in contrast, has a rare kind of star known as a Wolf-Rayet star at its center. Wolf-Rayet stars are extremely massive stars (at least 20 times more massive than the Sun) that are vigorously blowing their outer layers off under their own massive power generation (remember my talk about the Eddington Limit from the Eta Carinae picture?). Out Sun typically loses \(10^{-14}\) solar masses' worth of material each year; Wolf-Rayet stars typically lose \(10^{-5}\), a billion-fold increase.

The complex shape of NGC 2359 may be the result of interactions between the central star's stellar wind and a nearby molecular cloud, a region of greater-than-average gas and dust density. It's a rather faint nebula, so I'm glad I was able to get as much of it as I did (and it still required some pretty good histogram stretching to be this bright). The colors, though, are roughly correct, as I used wide-band filters instead of narrow-band ones.

Globular Cluster Photo Series (Part 16): NGC 3201

The globular cluster I have for you today is the first one I've imaged not found on Charles Messier's famous list. Instead, it bears the New General Catalogue (NGC) number 3201. The New General Catalogue was [and remains] one of the most comprehensive lists of deep-sky objects visible with typical amateur equipment ever, even though it was originally compiled in the 1880's. It contains a core group of 7,840 objects, and was later revised to include an additional 5,386.

Anyway, NGC 3201 is a lovely cluster far enough south in the constellation Vela the Sail that Messier wouldn't have been able to see it from his location in Paris. It's about 15,000 light-years away and perhaps 80 light-years across, which combines to give it the impressive visual size of 18.6 arcminutes, nearly two-thirds the width of the full Moon and twice as wide as M97 from yesterday.

In the northern hemisphere, most of the brightest objects are in the Messier catalog; thus, almost by definition, anything without a Messier number is not going to be as bright or as impressive as something with one (there are some exceptions both ways, but it's a general rule of thumb). In the southern hemisphere, this is not the case simply because Messier couldn't see down there.

This was well demonstrated the night I got the data for M79 which I showed in the previous post, and NGC 3201, which turned out to be the more impressive one. Here's the picture for comparison:

NGC 3201 in Vela.

M79 turned out to be another fairly small nondescript cluster (although its possible extra-galactic origins make it pretty cool in other ways). NGC 3201 was rather impressive by comparison. I was even able to make it out faintly by eye in one of our 14-inch telescopes, which was neat. Come to think of it, this is probably the southernmost globular cluster I've imaged to date.