## Monday, December 31, 2012

### Pau ʻo ka makahiki ʻelua-kaukani-ʻumikūmālua! 2012 is done!

Since, as you can see if you are reading this, the world did not end on December 21st, we can see that the end of the latest b'ak'tun in the Mayan calendar did not signal the end of the world any more than the ending of our calendar on December 31st does. The Mayan calculators simply had to pick a cut-off point for their future calendar predictions, and considering they chose one several hundred years past the point where their culture was actually really using it, I'd say they did a pretty good job. Sure, in these days of electronic computers it's trivial to extend the Gregorian calendar forward arbitrarily far in time, but in those days when all calculations were done by hand there comes a point where you just have to call it quits.

Anyway, happy New Year, everyone, I'll see you in 2013!

## Thursday, December 27, 2012

### Mele Kalikimaka ia kākou!

Merry Christmas everyone! I realized I'd never done a Christmas post before, and now that I've attempted it I remember why: the Internet at my parents' house is notoriously inconsistent when there are the slightest clouds in the sky, leading to an inability even to post for the past few days. Still, I hope that you all had a good Christmas, and a happy New Year.

## Thursday, December 20, 2012

### One Last Day of Work

Well, here I am, about to head off to my last day of work. Of course the only reason I'm working all day today instead of just tonight as I was originally scheduled is that my co-worker who was supposed to work today got stranded in the Mainland because of a canceled flight and couldn't make it home in time. Thus I'm filling in.

So, yeah. At the end of this week I'll be leaving my current job for my new one at the James Clerk Maxwell Telescope, which starts in January. Big changes are afoot.

## Tuesday, December 18, 2012

### One Ring Nebula to Rule Them All

Today I have something besides another globular cluster picture for your perusal. It's a picture of a nebula fairly famous in astronomical circles that I've seen prob-ably hundreds of times in the telescope (it's a popular target during the summer) but have never actually imaged before.

Perhaps it's appropriate that I have this picture less than a week after The Hobbit came out, as this object, Messier 57, is popularly known as the Ring Nebula. It's a small planetary nebula (small on the sky, not physically) found in the constellation Lyra, the Lyre, best seen during the summer and autumn. When I say small, it's only about 1.5 by 1 arc-minutes in diameter; compare that with Messier 55 from my last post, at 19 arc-minutes across. I've therefore cropped out the central region for easier viewing.

 Messier 57, the Ring Nebula, in Lyra, at 100% resolution from the camera.
The Ring Nebula is about 2,300 light-years from Earth, and is currently about two and a half light-years across. Measurements of its expansion rate suggest that it has been expanding for about $$1,610\pm240$$ years.

The processes forming the Ring Nebula have to do with the life cycles of stars. When stars about the mass of the Sun exhaust the hydrogen in their cores, they go through a complex process of fusing the helium produced by hydrogen fusion into heavier elements, then those into heavier elements, up the periodic table till they get stuck at carbon, having insufficient mass to fuse it to anything higher. During this time, due to other concurrent processes, their atmospheres swell up to become hundreds of times larger than before. As the star runs out of fusible material in its interior it gradually loses its grip on its outer atmosphere which puffs off into space, and which would have been observed starting sometime between A.D. 250 and A.D. 670.

This escaped atmosphere is what we're actually seeing when we look at the Ring Nebula. The core of the progenitor star has contracted down to a small white dwarf of mostly carbon about the size of Earth, but containing about the mass of the Sun. It currently has a temperature of about 125,000 K (~225,000 $$^\circ$$F) and lights up the surrounding atmosphere like a beacon as it blows away. The white dwarf at the center of the Ring Nebula is too faint to be seen in this picture, but is estimated to weigh about 20% more than the Sun currently does.

One of the reasons that I haven't had a picture of this famous (and not un-photo-genic) nebula up before, is because I'd already taken a picture of it...sorta. Sometime during the summer of 2010, I think, I tried imaging it using the narrow-band filters on the imager. Unfortunately, the night I chose had some very thin, high clouds, and I quickly learned that just because a star is bright enough over the entire visible light spectrum to serve as a guide star, does not mean it will be bright enough when you are only looking at the minuscule fraction of its light that comes through a narrow-band filter. Basically, it lost tracking during the exposure, the resulting picture was ruined, and I just never got around to imaging it again, there being plenty of other objects in the summer and autumn sky to keep me busy. This September I finally got around to imaging it and I'm glad I did, for completeness' sake if nothing else.

## Tuesday, December 11, 2012

### Globular Cluster Photo Series (Part 28): M55

Today I have another globular cluster picture for you, and this one just happens to be the next in the Messier catalog: Messier 55, in Sagittarius. This globular cluster is much closer than M54, at a moderately distant 17,600 light-years. It appears almost twice as large on the sky at 19.0 arc-minutes, but is a mere third its actual size at 96 light-years in diameter. It's also a lot less compact than M54 (class XI out of XII), and really looks quite nice.

 Messier 55 in Sagittarius.
Not every object in Charles Messier's catalog was discovered by him (and he gave credit where it was due), and M54 is one such object. It was discovered by an astronomer named Nicholas Louis de Lacaille from an observatory in South Africa in 1752. Messier, having heard of this discovery, tried several times to locate the cluster starting in 1764, but was stymied by its low apparent height from his location in Paris (it is located 30 degrees south of the celestial equator, which makes it rather difficult to see from mid-northerly latitudes). In fact, it wasn't until 1778 – 14 years later – that Messier was actually able to find it, after which he included it in his famous catalog of objects.

All in all, M55 is a rather nice looking cluster, if I say so myself.

## Saturday, December 8, 2012

### Globular Cluster Photo Series (Part 27): M54

It's been a while since I had any astronomical images to show, hasn't it? I haven't been able to use the imager for a while now, due to a combination of poor weather and being busy, but I do have a few images from September lying around that I never got around to reducing. Today I have the first of those, a picture of the globular cluster Messier 54 in Sagittarius.

Messier 54 is an interesting globular in several ways. For starters, it doesn't actually belong to our galaxy – or at least is a relatively recent acquisition. It appears to originate from the Sagittarius Dwarf Elliptical Galaxy (or SagDEG), a small nearby satellite galaxy of the Milky Way currently residing opposite the galactic core from us. SagDEG has four known globular clusters of its own, of which Messier 54 is the largest and main one.

Because it's on the other side of the core, M54 is the most distant cluster I've yet photographed, at a whopping 87,400 light-years away, easily surpassing the next most distance cluster I've shown here (M53, 58,000 light-years). For comparison, the Milky Way Galaxy itself is only about 100,000 light-years across. Despite its great distance, M54 still appears a relatively large 12.0 arc-minutes across on the sky, fully one-third the diameter of the full Moon. At its distance, that translates into the incredible diameter of about 306 light-years, making M54 larger than nearly every other globular cluster in the Milky Way (and certainly all the ones I've shown so far). It is also very luminous, shining with the light of 850,000 Suns, being outshone only by the brilliant cluster Omega Centauri (which is also a lot closer).

M54 is also one of the denser globular cluster, being a class III on the density scale (with class I being the densest and XII the least dense). It's also possible, according to a 2009 paper, that there may be a black hole with a mass 10,000 times that of the Sun at the center of the cluster, which is unusual for a globular cluster. All in all, it's a fascinating cluster.

## Saturday, December 1, 2012

### A New Room

Falling squarely in the category of "not particularly important, and only mildly life-altering", I've decided to move from my current room on the ground floor in the house where I live up to the empty room on the second floor.

This is exciting for me, as I don't think I've ever had a room above the ground floor (given the number of houses I've lived in across my lifespan, I actually had to pause to give that thought). Being on the second floor for this house means it'll be a bit warmer in general (good in the winter, not so nice in the summer), and also that I shouldn't have to worry about encountering centipedes anymore. The experience of "moving" has also pushed me to do some cleaning and tossing of stuff I no longer need. I don't think of myself as someone who spends much money on material items, so it's been a bit of a shock to see just how much stuff I've nevertheless managed to accumulate in my three years here.

I just started moving stuff upstairs today, but I'm hoping to be done or almost done by tomorrow night and actually be sleeping up there. Need to get some sleep now, as moving heavy stuff upstairs turned out to be more tiring than I expected. A hui hou!