Thursday, June 30, 2011

Globular Cluster Photo Series (Part 4): M22

Today's globular cluster is Messier 22, a nearby bright cluster in Sagittarius. Similar to M4, M22 is relatively close to us at a mere 10,600 light years, give or take a thousand. It is larger than M4 at about 100 light years across, but smaller than Omega Centauri or M13, though appearing about as bright due to its closer distance (in fact, it is the third brightest globular cluster in the sky after Omega Centauri and 47 Tucanae, just edging out M13 for the distinction). It has an apparent diameter of 32 arcminutes, making it almost the same size as the Moon, and about in the middle of the clusters shown so far. It has a somewhat smaller number of stars, only about 70,000.

Messier 22 in Sagittarius. Click for larger image.
It also has the distinction of being quite possibly the first globular cluster discovered, as far back as 1665 by an amateur astronomer by the name of Johann Ihle while he was observing Saturn in Sagittarius (M22 lies very near the ecliptic, the line the planets and Sun seem to traverse on the sky due to our perspective). Although Omega Centauri and 47 Tucanae were known well before this time (Omega Centauri as far back as the time of Ptolemy), they were thought to be simply faint stars, which is where their names come from.

M22 is also somewhat unique in that it is one of only four of the Milky Way's numerous globular clusters known to contain a planetary nebula, the wispy gaseous cocoon of a Sun-like star as it nears the end of its time on the main sequence and starts becoming a white dwarf. It's much too small and faint to be visible in my picture, though. I have some images I took of planetary nebulae within the Milky Way that I'll post when I run out of my backlog of globular cluster images. Also when I'm done with the current run of images I plan to make a little graphic showing the relative sizes of the various globular clusters we've seen.

Wednesday, June 29, 2011

Globular Cluster Photo Series (Part 3): M13

Today we're taking a look at another of the biggest and brightest globular clusters in the sky, Messier 13, also known as the Great Globular Cluster in Hercules. (It's located around the area of his kidney. We can but hope it's not a Herculean kidney stone!) It is nearly the same size as Omega Centauri, about 170 light years across. However, it has only a 3rd as many stars, about 300,000.

Messier 13, the Great Globular Cluster in Hercules. Click for larger image.
Although it's as large as Omega Centauri, M13 appears 2/3 as large on the sky because it is almost twice as far away; 25,000 light years compared to Omega Centauri's ~16,000. (Its apparent diameter is 20 arcminutes compared to Omega Centauri's 36.3, so M13 is about 2/3 the size of the full Moon on the sky.)

Other than that, I don't have too much to say about M13. It, Omega Centauri, and another cluster called 47 Tucanae are generally considered the best and most beautiful globular clusters. 47 Tucanae is just below the horizon from Hawai‘i, so I won't be showing you any pictures of it. In terms of visual impressiveness it will probably go down from here since most globular clusters are either smaller or further away (or both) than these three, leading them to appear smaller on the sky.

Of course, one reason I started this project was to catalog the differences between the many Milky Way globular clusters. On the face of it they're not particularly interesting, big balls of stars held together by self-gravitation. Just as all stars are big balls of gas held together by self-gravitation. And yet, just as there is almost infinite variation among stars, I'm already starting to see differences just between the three globular clusters I've shown here. Some are larger, some smaller, some very tightly packed, some less so. My goal for this series is to get a sense for that same variability found in globular clusters.

Tuesday, June 28, 2011

Globular Cluster Photo Series (Part 2): Omega Centauri

First off, an apology. If you read my post from yesterday, it contained a grave error -- namely, that the object in the photo was not, after all, Messier 4, but the object I intend to show you today, Omega Centauri.

I'm still scratching my head trying to figure out how it happened, unless I had a critical failure in reading the file names. However, the situation has now been rectified, and a picture of M4 has been reduced and added to the post in question.

Today's globular cluster is Omega Centauri, commonly called the most beautiful globular cluster in the night sky. You may have already seen it if you read my post yesterday before I fixed it, but I've re-reduced the picture and I like this version better. Omega Centauri is the brightest and largest cluster found orbiting the Milky Way, and the second largest in the Local Group of Galaxies (one of the clusters orbiting the Andromeda galaxy is larger). It is located a mere 15,800 light years from us (give a take a thousand light years or so), making it just about twice as far away as M4, which we looked at yesterday. However, if you compare the two pictures, you'll see that Omega Centauri looks a bit bigger; this is partly because it is bigger, being around 170 light years across compared to M4's 70. It has about the same apparent diameter on the sky, too, being about the size of the full moon (36.3 arcminutes). It is just bright enough to be faintly visible with the naked eye (I've seen it from Mauna Kea).

The fact that it appears star-like to the naked eye is actually responsible for its name. Back in 1603 a German astronomer by the name of Johann Bayer created a sky catalog called Uranometria in which he assigned Greek letters to the prominent stars of each constellation. Because of its star-like appearance Omega Centauri received a Greek letter like any other star. Though the fact that the letter it received comes at the end of the Greek alphabet shows that it wasn't considered very important, which makes sense, since it doesn't appear very bright in the sky.

Omega Centauri in Centaurus. Click for larger image.
At first glance, you can tell that Omega Centauri is a lot brighter and more compact than M4. Some estimates place it at a million stars, on the high end of the several-hundred-thousand-star range common to globular clusters. In fact, the high number of stars combined with some other unusual aspects of Omega Centauri lead some to suspect that it is in fact the core of a smaller galaxy whose outer stars were absorbed into the Milky Way. Kapteyn's Star, a red dwarf a mere 13 light years from Earth, may even be one such star.

Another interesting fact about Omega Centauri (and other globular clusters in general) is its high stellar density. Near the center stars are estimated to be packed so tightly that the mean distance between them is a mere 0.1 light year, or only around 6,300 Astronomical Units (the average distance between the Earth and the Sun, abbreviated AU). Even with that helpful comparison, that number may not mean much to you (it didn't even for an astronomy student like me), so I took the liberty of creating this helpful picture:


In the top half of the picture we see the Sun and its nearest neighbors Proxima Centauri and Alpha Centauri A and B (interestingly our nearest neighbors lie very close in the sky to Omega Centauri). In this picture, one light year is 100 pixels, so the closest star to our Sun, Proxima Centauri, is 424 pixels (4.24 light years) away, while Alpha and Beta are a little further at 4.37 light years. Note that the sizes of stars in the picture are vastly over-exaggerated for visibility; one pixel is 0.01 light years, or about 632 AU. For comparison, the orbit of Neptune is almost exactly 60 AU in diameter.

In the bottom half we have a representation of the stellar density of Omega Centauri. The stars arranged in the regular grid at the bottom left are 0.1 light year apart, but since I rapidly tired of placing them in regular grid rows 0.1 light year apart (an unrealistic arrangement in nature), the rest are placed at random and slightly less dense positions. Since the density decreases as you go out from the center, this gives a semi-realistic view of the center of the cluster.

Of course, at the scale represented in the picture Omega Centauri would be approximately 26 times as wide as the picture, so imagine a giant sphere of stars about 10 feet in diameter packed about as closely shown in the picture. That's a lot of stars.

Monday, June 27, 2011

Globular Cluster Photo Series (Part 1): M4

Today I thought I'd start off a little series of some of the objects I've been spending my time imaging up on Mauna Kea while volunteering. I've imaged a lot of things, mostly on a "let's see what's out tonight, pick something that sounds interesting, and image it" basis, but last fall I had an idea to try and photograph as many of the Milky Way's globular clusters as I could. Having cracked the secret to getting pictures from my data, I start off by presenting to you an image of the globular cluster Messier 4, in Scorpius.

M4 in Scorpius. Click for larger view.
It looks like there's another small cluster (possibly of the open variety) in the bottom right of the frame, but I don't know what it's called.

Messier 4 is a very rich globular cluster, and was the first globular cluster in which individual stars were resolved. It also happens to one of the closest globular clusters to Earth, at a mere 7,200 light years. Because it's so close, it appears fairly large on the sky: depending on where you want to draw the cutoff point, it appears nearly the same size as the full moon does, 36.0 arcminutes across (the moon varies between 29.3 to 34.1 arcminutes depending on its position in orbit). For ease of comparison, I've decided not to crop the images from the size they come out of the camera so you can easily see the difference in apparent sizes between objects. (This might come back to bite me when I'm looking at really small clusters, especially since M4 is one of the larger ones on the sky, but we'll see how it goes.) Keep in mind that apparent size differences are not absolute size differences, which is why I will post the actual size when possible; M4 is about 35 70 light years across. (35 light years is its radius.)

Finally, M4 has the distinction of being the first globular cluster in which a millisecond pulsar was discovered.

Saturday, June 25, 2011

Supernova picture! This time with color!

After my nearly one-subject posts the last week or two you guys will probably never want to see another supernova, but I'm quite proud of myself for figuring out how to get color working. I originally thought it was as simple as “put red image in red channel, green image in green channel, blue image in blue channel, et voila!”. Turns out it's not, and I got discouraged when I ended up with a bizarrely colored image looking nothing like what I thought it would. However, it turns out the process is not much more difficult than that, merely requiring iterative manual adjustment of the color curves until it looks the way you want it.

Supernova SN2011dh in M51.
In this picture you can clearly see the spiral arms of M51 outlined by the blue light from hot young stars with dark dust lanes obscuring parts of it, the same kind of dust lanes that are responsible for the dark patches seen in our own Milky Way. I'm not a hundred percent sure about the color balance, but this represents the kinds of color you might be able to see if you could let light accumulate on your retina for 5 minutes at a time, instead of refreshing many times a second.

Wednesday, June 22, 2011

Now you're thinking with Python...

Today I created something new and wonderful, a master database containing all the information on all the data Dr. Takamiya and I have collected for our research. This is a big database. We have 67,050 individual spectra which come in pairs (one red, one blue), for a total of 33,525 individual spaxels. Currently there are 46 different pieces of information for each spaxel, for a combined total of 1,542,150 pieces of information contained therein. The information for each spaxel was spread out over 5 different files prior being collected and organized (that's 5 files for each spaxel, there are actually a total of 596 files for the individual spaxels, plus one more that contains certain information for each group of 225 spaxels that makes up one-half of an observation). This is a single text file that's 11 megabytes in size, bigger than the pictures my camera takes at maximum resolution (though not so large as to be unmanageable).

I'm pretty excited about this as you can imagine. This is the culmination of over a year of work on my part. I've really enjoyed working with my mentor Dr. Takamiya for the entire time. She wonderfully handled the balance between letting me try and fail and learn on my own and being there to help when I really couldn't figure something out. For the first several months I was too ashamed to admit that I didn't fully comprehend the big picture of what we were doing, but she was always willing to explain it to me again and able to show me the next little step to take to get there (and yes, I finally understand it now). When I say the database is the culmination of work on my part, I really mean it; while she showed me the way to go, she left nearly all the actual design and implementation decisions up to me, and the process indelibly bears my mark in many ways (for good or bad). I've grown in so many ways as a Python programmer during this time I can hardly begin to list them all, though I think the biggest is my recent sudden understanding of Python classes, something that would never have happened if I hadn't spent so much time thinking and struggling and working with Python over the last year.

Of course, this reminiscing isn't to say that we're done. Far from it! In some ways the real work is just getting started. Now we can begin rigorously plotting the data to really tease out the relationships that have been hinted at previously. That should keep us occupied for some time...

Saturday, June 18, 2011

More supernova pictures.

Hello everyone, I know it's been a while since I last posted, I've been busy helping out with VBS every night. Also, I was hoping to have a color image of that supernova for you, but I'm still working out how make one. So in lieu of that you get another gray-scale one. I took this one last Saturday night.

Messier 51 with supernova visible in the upper-right area. See the post below for an exact pointer.

If you think it looks very similar to the picture in my last post, well, you're right. I don't know if it is possible to tell by comparison, but when blinking between the two images the supernova is noticeably brighter in the later image (this one) than the earlier one. Not much, but a noticeable amount. I'll try to get another shot of it sometime next week, and see if it has started to fade at all by that point. Pretty interesting stuff!

Saturday, June 11, 2011

Supernova! For real this time!

Remember that image I mentioned in my last post? Well, I reduced it, and it came out pretty nice. Unfortunately, it's in gray-scale because clouds came in and covered the galaxy before I could get the color exposures, but it still shows remarkable detail.

Messier 51 with supernova SN2011dh. Companion galaxy NGC 5195 at bottom.
I'd like to draw your attention to just how remarkable this star is. Every other individual star you see in the picture is within the Milky Way Galaxy - that bright one on the right might just be visible with the naked eye (I'm not sure it's the same star, but I can just make one out in the area where M51 is). Each of these Milky Way stars is, at most, a few tens of thousands of light-years away. Supernova SN2011dh is around 25 million. And it's as bright as or brighter than many of the stars in the picture. Now factor in the fact that the brightness of an object (which is what is represented here) decreases as the square of the distance increases, and that's one seriously bright star. (For comparison, none of the other stars in M51 can be made out individually in this picture - the ones that appear to be part of it are really foreground Milky Way stars.)

In fact, when this supernova first exploded, it was emitting as much energy individually as the rest of the hundreds of billions stars in M51 combined. The reasons it doesn't appear as bright as the rest of the galaxy are 1) it was about five days old by the time I took this picture, so it had begun to fade a little. And 2) most of that energy is not in the visible portion of the spectrum. Remind me sometime when it's not so late to explain the details behind a supernova type IIa.

As an aside, you can't see them in this picture because of the exposure settings I chose, but I caught two extremely faint satellite trails in my exposures, one of which neatly passed diagonally from lower-left to upper-right between M51 and the star on the right.

Thursday, June 9, 2011

Classes!

There are two things exciting me today, so I decided I'd write about both of them. First of all, to resolve yesterday's cliffhanger, yes, I was able to see the supernova. Not by eye, but I was able to capture an imager of it using the imaging telescope at the Vis (another volunteer there told me he'd spent the night before trying to see it visually with the largest telescope at the Vis and had no luck, so I didn't bother looking for it visually).

I haven't had time to reduce the image yet due to the other thing exciting me, but hopefully I can show you all pretty soon what it's like to see a single star putting out more energy than an entire galaxy 25 million light years away.

The other thing exciting me is that I suddenly learned how to use classes in Python, my favorite scripting language. Classes are basically user-defined objects, and a definite step up in the abstraction department. The reason I'm so excited about it is because of the way it happened.

Now, before Tuesday, I'd never used a class in Python, nor did I understand them. I'd read the documentation introducing them before two or three times, but couldn't really make heads or tails of it. Then, Tuesday, as Dr. Takamiya and I were trying to pin down an unrelated bug in my code, I became painfully aware just how convoluted my data was getting in my script. Lists were stacked in other lists, which were stacked in still more lists, and it was becoming a nightmare remembering what was what while executing the script.

Finally I took a little break to think, and the thought popped into my mind “I think I need to use a class for this”. Remember, I had zero prior experience with classes up to that point. However, since we weren't really getting anywhere the way we were going, I went home to do some quiet thinking and see if this idea would pan out.

And did it ever! I found and read the documentation on classes again, and it's as if everything had clicked into place in my mind. I understood everything perfectly clearly. I had to run off to go up to Mauna Kea soon afterwards, but I had the same experience today when I took it up again. It still feels somewhat surreal, as if someone just flipped a switch in my mind. I see it as another case of the fact that sometimes, at least for me, I need to figure out something on my own before I can effectively learn it. I essentially came up with the idea, “I need to be able to do this in Python”, and lo and behold, there exists a method to do this. I'd never appreciated it before because I hadn't really needed like I did recently, but when I finally did, it came practically like second nature. (If you're interested, classes are basically what I said before, user-defined objects. You can use them as containers to store arbitrary data, which is mostly what I was using them for, but they're much more versatile than that. Hard to explain in a few sentences. Let's just leave it that they're really useful and handy.)

Wednesday, June 8, 2011

Supernova!

This evening I'm heading up to Mauna Kea for a really exciting chance to see a supernova with my own eyes!


Err...the “exploded-star giant-kaboom!” kind of supernova, not a bottle of one of my favorite flavors of Mountain Dew. This newly-discovered supernova is in the Whirlpool Galaxy, M51, which is just off the handle of the Big Dipper, so it's nice and visible from Hawai‘i this time of year. If I'm extremely lucky, I may even be able to get a picture of it, although the chances of that pretty low, realistically. Still, if I can manage to find it, I'll be sure to give you a description.

Here's a picture of the Whirlpool Galaxy from Hubble, by the way. This is one of the galaxies I used for inspiration in my picture I posted  two weeks ago, incidentally. You can judge for yourself how good my efforts to emulate it were.

Messier 51, the Whirlpool Galaxy, and companion elliptical galaxy NGC 5195.

Wednesday, June 1, 2011

Heavenly Island in a Sea of Cloud

Sunday Jonathan and I went up to Mauna Kea as volunteers to help with the summit tour. It seems each time I go to see the silverswords I find another great photo opportunity. Someone created this pretty rock pattern around one particularly large and healthy plant:


A couple visiting Hawaiʻi showed up while we were there, so I pointed out some of the silverswords, and, when they seemed interested, shared a few of the things I've learned about them -- and was promptly asked if I was a botanist!

“The Botanist”
The wind at the summit was downright bone-chillingly frigid. I don't remember ever being so cold up there before. It was actually warmer inside the Keck telescope dome (or at least it felt like it)! Strangely, despite the Arctic weather up top, it was surprisingly mild and warm down at the Vis, even into the night. Jonathan and I went to catch the sunset from a cinder cone near the Vis, and the experience, sans wind, was much more pleasant than the last time we tried it. It was clear enough that we could actually see Hualālai to the west, a rare occurrence:

Hualālai: Ke Mokupuni Lani i ke Kai Ao (Heavenly Island in a Sea of Cloud).
All in all, a most pleasant day. I should probably end this post and get to bed, however. A hui hou!